ALBERT

Description: In the future, climate models predict an increase in global surface temperature and during winter a changing of precipitation from less snowfall to more raining. Without protective snow cover, freezing can be more intensive and can enter noticeably deeper into the soil with effects on C cycling and soil organic matter (SOM) dynamics. We removed the natural snow cover in a Norway spruce forest in the Fichtelgebirge Mts. during winter from late December 2005 until middle of February 2006 on three replicate plots. Hence, we induced soil frost to 15 cm depth (at a depth of 5 cm below surface up to –5°C) from January to April 2006, while the snow-covered control plots never reached temperatures 〈 0°C. Quantity and quality of SOM was followed by total organic C and biomarker analysis. While soil frost did not influence total organic-C and lignin concentrations, the decomposition of vanillyl monomers (Ac/Ad) V and the microbial-sugar concentrations decreased at the end of the frost period, these results confirm reduced SOM mineralization under frost. Soil microbial biomass was not affected by the frost event or recovered more quickly than the accumulation of microbial residues such as microbial sugars directly after the experiment. However, in the subsequent autumn, soil microbial biomass was significantly higher at the snow-removal (SR) treatments compared to the control despite lower CO 2 respiration. In addition, the water-stress indicator (PLFA [cy17:0 + cy19:0] / [16:1ω7c + 18:1ω7c]) increased. These results suggest that soil microbial respiration and therefore the activity was not closely related to soil microbial biomass but more strongly controlled by substrate availability and quality. The PLFA pattern indicates that fungi are more susceptible to soil frost than bacteria.

Description: Intensive land use may affect soil properties ( e.g., decreased soil organic matter [SOM] content) and, consequently, reduce crop yields considerably. One way of counteracting the loss of SOM and stimulating plant productivity could be the use of organic residues from agro-industrial processes as bioactive products. The present study was focused on the possible effects of phenol-containing organic substances derived from agro-industrial by-products on maize ( Zea mays L.) metabolism in a pot experiment. Plants were grown for 12 d in a nutrient solution in the absence (control) or in the presence of either a cellulosolitic dry apple hydrolyzate (AP) or a dry blueberry cool extract (BB) applied at two rates (0.1 and 1 mL L –1 ). Both products increased root and leaf biomass and led to higher concentrations of macronutrients in the plant tissue. AP and BB also had a positive impact on nitrogen (N) metabolism stimulating the activity and gene expression of phenylalanine ammonia-lyase, a key enzyme of the phenylpropanoid pathway. Furthermore, both products increased leaf concentrations of phenols (+ 28% and 49% for AP and BB, respectively) and flavonoids (+ 22% and 25% for AP and BB, respectively). From our results it can be assumed that residues from agro-industry may be successfully used as bioactive products in agriculture to increase plant yield and resistance to stress conditions.

Description: An agricultural use of reclaimed coal-mine spoil banks is limited to nonfood crop uses and provides potential for biofuel crops. Two high-biomass crops— Galega orientalis and Helianthus tuberosus —were cultivated in a greenhouse pot experiment conducted in sterilized and nonsterile spoil bank clay. We aimed (1) to determine the possibility of reducing the applied rate of organic amendments (thus decreasing the costs of spoil-bank reclamation) and (2) to assess whether the inoculation with arbuscular mycorrhizal fungi (AMF) can improve plant growth and biomass accumulation of bioenergy crops even in nonsterile soil containing naturally occurring AMF. The spoil substrate was either unamended or treated with a mixture of composted urban waste and ligno-cellulose at a rate corresponding to 40 t ha –1 . Three native AMF isolates or three isolates from the International Bank of Glomeromycota (BEG) originating from man-made ecosystems were used for inoculation. Generally, both plant species positively responded to both mycorrhizal inoculation and organic amendment. While G. orientalis did not show any preferences towards the AMF inoculum origin in the nonsterile soil, for H. tuberosus the specific combination of organic amendment and BEG isolates resulted in highest yields of shoot biomass. The study shows that the successful planting of both tested crops requires the organic amendment. However, its dosage can be substantially reduced. The effectiveness of mycorrhizal inoculation can vary for the combination of plant species and the origin of the applied AMF.

Description: Iodine is an essential element in the human diet, and iodine deficiency is a significant health problem. No attempts to increase iodine content in plant-derived food (biofortification) have so far been particularly effective. We studied iodine uptake in tomato ( Solanum lycopersicum L.) to evaluate whether it is possible to increase the iodine concentration in its fruits. Iodine translocation and storage inside tomato tissues were studied using radioactive iodine. Potassium iodide was also supplied at different concentrations to tomato plants to evaluate the resulting iodide concentration both in the vegetative tissues and the fruits. The results indicate that iodine was taken up better when supplied to the roots using hydroponically grown plants. However, a considerable amount of iodine was also stored after leaf treatment, suggesting that iodine transport through phloem also occurred. We found that tomato plants can tolerate high levels of iodine, stored both in the vegetative tissues and fruits at concentrations that are more than sufficient for the human diet. We conclude that tomato is an excellent crop for iodine-biofortification programs.

Description: Citrus established in calcareous soils can be affected by iron (Fe)-deficiency chlorosis which limits yield and the farmers' income. The degree of deficiency depends on the rootstock, but the resistance to Fe chlorosis still requires further investigation. To study physiological parameters of citrus rootstocks that could be used to evaluate resistance to Fe deficiency, plants of Troyer citrange ( Citrus sinensis L. Osb. × Poncitrus trifoliata L. Raf.), Carrizo citrange, Volkamer lemon ( Citrus volkameriana Ten. & Pasq.), alemow ( Citrus macrophylla Wester), and sour orange ( Citrus aurantium L.) were grown in nutrient solutions with 0, 5, 10, 15, or 20 μM Fe. For each rootstock, plant height, root and shoot dry weights, and concentration of Fe in the shoots and roots were measured at the end of the experiment. Chlorophyll (CHL) concentration was estimated throughout the experimental period using a portable CHL meter (SPAD-502) calibrated for each rootstock. At the end of the experiment, CHL fluorescence parameters were measured in each rootstock with a portable fluorimeter. Maximal and variable fluorescence values indicated that the photochemistry of Troyer was more affected by a low concentration of Fe in the nutrient solution than that of other rootstocks. To compare rootstocks, the absolute CHL concentration was converted into relative yield by employing a scaling divisor based on the maximum value of total CHL in plants without Fe-deficiency symptoms. Exponential models were developed to determine the minimum Fe concentration in nutrient solution required to maintain leaf CHL at 50% of the maximum CHL concentration (IC50). Models were also developed to assess the period of time the rootstocks were able to grow under Fe-stress conditions before they reached IC50. Volkamer lemon and sour orange needed the lowest Fe concentration (between 4 and 5 μM Fe) to maintain IC50, and Troyer citrange had the highest Fe requirement (14 μM Fe). Citrus macrophylla and Carrizo citrange required 7 and 9 μM of Fe, respectively. Similarly, Volkamer lemon and sour orange rootstocks withstood more days under total Fe depletion or with a low concentration of Fe (5 μM Fe in nutrient solution) until they reached IC50, compared to the other rootstocks. The approach used led to a classification of the rootstocks into three categories, regarding their internal tolerance to Fe chlorosis: resistance (sour orange and Volkamer lemon), intermediate resistance (C . macrophylla and Carrizo citrange), and reduced resistance (Troyer citrange).

Description: Trees interact in a complex manner with soils: they recycle and redistribute nutrients via many ecological pathways. Nutrient distribution via leaf litter is assumed to be of major importance. Beech is commonly known to have lower nutrient concentrations in its litter than other hardwood tree species occurring in Central Europe. We examined the influences of distribution of beech ( Fagus sylvatica L.), ash ( Fraxinus excelsior L.), lime ( Tilia cordata Mill. and T. platyphyllos Scop.), maple ( Acer spp. L.), and clay content on small-scale variability of pH and exchangeable Ca and Mg stocks in the mineral soil and of organic-C stocks in the forest floor in a near-natural, mature mixed deciduous forest in Central Germany. The soil is a Luvisol developed in loess over limestone. We found a positive effect of the proportion of beech on the organic-C stocks in the forest floor and a negative effect on soil pH and exchangeable Ca and Mg in the upper mineral soil (0 to 10 cm). The proportion of ash had a similar effect in the opposite direction, the other species did not show any such effect. The ecological impact of beech and ash on soil properties at a sample point was explained best by their respective proportion within a radius of 9 to 11 m. The proportion of the species based on tree volume within this radius was the best proxy to explain species effects. The clay content had a significant positive influence on soil pH and exchangeable Ca and Mg with similar effect sizes. Our results indicate that beech, in comparison to other co-occurring deciduous tree species, mainly ash, increased acidification at our site. This effect occurred on a small spatial scale and was probably driven by species-related differences in nutrient cycling via leaf litter. The distribution of beech and ash resulted not only in aboveground diversity of stand structures but also induced a distinct belowground diversity of the soil habitat.

Description: Several chemical and microbial properties of mine soils need to be measured for comprehensive assessment of the reclamation success. The objective of this study was to evaluate the ability of NIR spectroscopy to predict organic C (C org ), total N (N t ), and several microbial properties of mine soils reclaimed for forestry. Soils samples ( n = 154) were collected at two reclaimed areas in central and S Poland, and their spectra in the NIR region (including the visible range, 400–2500 nm) were recorded. A half of the samples was used to develop calibration equations, and another half was used for validation. The modified partial least squares regression was applied to build calibration equations using the whole spectrum (0 to 2nd derivative). The best predictions were obtained for C org and N t (ratio of standard deviation to standard error of prediction in the validation stage [RPD] = 3.4 and 4.1; the regressions coefficients [ a ] of linear regression [measured against predicted values] = 0.94 and 0.96; correlation coefficients [ r ] = 0.96 and 0.97, respectively). Very well predictive models applicable for quantitative measurements were obtained also for microbial biomass, basal respiration, and the activities of dehydrogenase and acid phosphatase (RPD = 2.3–2.5, a = 0.90–0.99, r = 0.90–0.92). Prediction of urease activity was slightly worse (RPD = 2.1, a = 0.88, r = 0.87) but sufficient for rough estimation. The obtained results indicated the ability of NIR spectroscopy to predict complex soil microbial properties. Therefore, application of this analytical method may improve the assessment of recovery of microbial functions in reclaimed post-mining barrens.

Description: Several algorithms exist for the calibration procedures of near-infrared spectra in soil-scientific studies, but the potential of a genetic algorithm (GA) for spectral feature selection and interpretation has not yet been sufficiently explored. Objectives were (1) to test the usefulness of near-infrared spectroscopy (NIRS) for a prediction of C and N from char and forest-floor Oa material in soils using either a partial least squares (PLS) method or a GA-PLS approach and (2) to discuss the mechanisms of GA feature selection for the examined constituents. Calibration and validation were carried out for measured reflectance spectra in the visible and near-IR region (400–2500 nm) on an existing set of 432 artificial mixtures of C-free soil, char (lignite, anthracite, charcoal, or a mixture of the three coals), and forest-floor Oa material. For all constituents (total C and N, C and N from all coals and from the Oa material, C derived from mixed coal, charcoal, lignite, and anthracite), the GA-PLS approach was superior over the full-spectrum PLS method. The RPD values (ratio of standard deviation of the laboratory results to standard error of prediction) ranged from 2.4 to 5.1 in the validation and indicated a better category of prediction for three constituents: “approximate quantitative” instead of a “distinction between high and low” for C derived from mixed coal and “good” instead of “approximate quantitative” for C and N derived from all coals. Overall, this study indicates that the approach using GA may have a greater potential than the PLS method in NIRS.

Description: Several genes in the aspen genome have been modified to generate stem wood with lower lignin content and an altered lignin composition. Lower lignin in wood reduces the time and energy required for pulping. Further, this modification can also increase the allocation of photosynthate to cellulose and total biomass production, potentially increasing CO 2 -sequestration capacity. However, widespread planting of trees with altered lignin content and composition could alter soil organic-C dynamics in complex ways. To further examine the effects of altered lignin biosynthesis on plant growth and accrual of soil organic C (SOC), we conducted a repeated greenhouse study with four lines of transgenic aspen ( Populus tremuloides Michx.) and one wild-type (control) aspen. Accrual of aspen-derived SOC was quantified by growing aspen trees (C3 plants) in C4 soil and measuring changes in the natural abundance of δ 13 C. We measured plant growth, biomass, and C content and combined these data with SOC measurements to create C budgets for the plant mesocosms. Lignin modifications resulted in differences in the accrual of aspen-derived SOC and total mesocosm C, primarily due to differences in biomass between genetically modified lines of aspen. One genetic alteration (low lignin, line 23) was able to perform similarly or better than the wild-type aspen (control, line 271) without altering SOC. Alterations in lignin structure (S : G ratios) had negative effects on biomass production and SOC formation. The addition of new (aspen-derived) SOC was proportional to the loss of existing SOC, evidence for a priming effect. The pool of new SOC was related to total plant biomass, suggesting that the effects of lignin modification on SOC are driven by changes in plant growth.

Description: Wild barley ( Hordeum sp. ) germplasm is rich in genetic diversity and provides a treasure trove of useful genes for crop improvement. We carried out a comprehensive program combining short-term hydroponic screening via hematoxylin-staining of root-regrowth procedure and filter paper–based evaluation of diverse germplasm in response to Al/acid stress using 105 annual Tibetan wild barley and 45 cultivated barley genotypes. Root elongation among the 105 Tibetan wild barley genotypes varied significantly after Al exposure, ranging from 62.9% to 80.0% in variation coefficients and 4.35 to 4.45 in diversity index. These genotypic differences in Al resistance were fairly consistent in both the hydroponic and filter paper–based evaluations: XZ16, XZ166, and XZ113 were selected as Al-resistant genotypes, and XZ61, XZ45, and XZ98 as Al-sensitive wild genotypes. Furthermore, significantly lower Al concentrations in roots and shoots were detected in the three selected Al-resistant genotypes than in the three sensitive genotypes in the filter paper–based experiment. Meanwhile, XZ16 was the least affected by Al toxicity in regard to reduced SPAD value (chlorophyll meter readings), plant height, root length, dry biomass, tillers per plant, and chlorophyll fluorescence (Fv/Fm) in the long-term hydroponic experiment compared with the Al-resistant cultivated barley cv. Dayton, while XZ61 had the severest stress symptoms.

Description: Simplified algebraic equations are derived to calculate directly the Brooks and Corey model parameters using data obtained from one-step outflow experiments and saturated hydraulic conductivity. The suggested method has been demonstrated only for horticultural substrates and is verified experimentally for four substrates with satisfactory agreement of the results.

Description: Fine roots from the soil archive of the Swedish National Forest Soil Inventory, collected in 1964, 1972, 1985, and 1998, were analyzed for 14 C contents. Two different methods of estimating residence time were compared. Residence time of root C was estimated to be 8 y using a steady state 1-pool model.

Description: Appropriate management of P from slurry can increase crop production and decrease nutrient loss to water bodies. The present study examined how the application of different size fractions of dairy slurry influenced the quantity and composition of P leached from grassland in a temperate climate. Soil blocks were amended (day 0 = start of the experiment) with either whole slurry (WS), the 〉 425 μm fraction (coarse slurry fraction, CSF), the 〈 45 μm slurry fraction (fine liquid slurry fraction, FLF), or not amended, i.e., the control soil (CON). Deionized water was added to the soil blocks to simulate six sequential rainfall events, equivalent to 250 mm (day 0.2, 1.2, 4.2, 11.2) or 500 mm of rainfall (day 18.2 and 25.2), with leachates collected the following day. The results showed that total dissolved P (TDP), dissolved reactive P (DRP), dissolved unreactive P (DUP), orthophosphate, phosphomonoester, and pyrophosphate concentrations generally decreased with the increasing number of simulated rain events. Total dissolved P was leached in the following order WS 〉 FLF ≈ CSF 〉 CON. Dissolved organic C was correlated with TDP, DRP, and DUP in leachates of all treatments. The highest concentrations of dissolved phosphomonoesters and pyrophosphate (147 μg P L –1 and 57 μg P L –1 , respectively) were detected using solution 31 P-NMR spectroscopy in the WS leachates. Overall, there were significant differences observed between slurry treatments ( e.g., relative contributions of inorganic P vs. organic P of dissolved P in leachates). Differences were independent from the rate at which slurry P was applied, because the highest dissolved P losses per unit of slurry P applied were measured in the FLF, i.e., the treatment that received the smallest amount of P. We conclude that the specific particle-size composition of applied slurry influences dissolved P losses from grassland systems. This information should be taken in account in farm-management approaches which aim to minimizing dissolved slurry P losses from grassland systems.

Description: Several methods are used for the extraction of soil solution. The objective of this study was to find out to what extent the different extraction methods yield complementary or equivalent information. Soil solutions were sampled once at 10 different forest sites in Germany, with 4 sampling points per site, using 5 different extraction methods. Concentrations of the major ions in the 1:2 extracts and the equilibrium soil-pore solutions (obtained from percolation of field-fresh soil cores) were generally lower than in desorption solutions, suction-cup solutions, and saturation extracts. Surprisingly, the latter three methods generally yielded equivalent results. However, possible systematic differences between these methods could have been masked by the high small-scale spatial variability within the sites.

Description: A standard and a high manganese (Mn) level (10 and 160 μM) were combined with a standard and a high zinc (Zn) level (4 and 64 μM) in the nutrient solution supplied to cucumber in closed-cycle hydroponic units to compensate for nutrient uptake. The concentrations of all nutrients except Mn and Zn were identical in all treatments. The objectives of the experiment were to establish critical Zn and Mn levels in both nutrient solutions and leaves of cucumber grown hydroponically, to assess the impact of gradual Zn and/or Mn accumulation in the external solution on nutrient uptake and gas exchange, and to find whether Mn and Zn have additive effects when the levels of both ions are excessively high in the root zone. The first symptoms of Mn and Zn toxicity appeared when the concentrations of Mn and Zn in the leaves of cucumber reached 900 and 450 mg kg –1 in the dry weight, respectively. Excessively high Mn or/and Zn concentrations in the leaves reduced the fruit biomass production due to decreases in the number of fruits per plant, as well as the net assimilation rate, stomatal conductance, and transpiration rate, but increased the intercellular CO 2 levels. Initially, the Mn or Zn concentrations in the recirculating nutrient solution increased rapidly but gradually stabilized to maximal levels, while the corresponding concentrations in the leaves constantly increased until the end of the experiment. The uptake of Mg, Ca, Fe, and Cu was negatively affected, while that of K and P remained unaffected by the external Mn and Zn levels. The combination of high Mn and Zn seems to have no additive effects on the parameters investigated.

Description: A pot experiment with wheat plants was carried out to study how late application of nitrogen (N) fertilizer affects the use of pre-anthesis N reserves during the grain-filling period. Increasing doses of N fertilizer were applied (0, 40, and 52 mg N plant –1 ), either in two amendments (growth stages GS20 and GS30, according to Zadoks scale) or in three amendments (GS20, GS30, and GS37). The experiment was arranged in a complete randomized three-block design with 129 plants per treatment. The plants were watered daily, harvested every 2 d between anthesis and maturity, and were separated into roots, leaf sheaths, leaf blades, and ears for further N determination. Grain N concentration improved due to a late N application in GS37 by 14% (higher N dose) and by 7% (further splitting the same N-fertilizer dose, respectively). The higher the N-fertilizer dose applied, the greater was the amount of pre-anthesis reserves in vegetative organs, these reserves became later available for remobilization. Although splitting the same N dose in three amendments did not increase the N reserves, these reserves were more efficiently remobilized allowing an improvement in grain N concentration. The fertilizer management did not change the temporary pattern of N accumulation in the ear, but did induce a change in the amount of N remobilized and in the contribution of each organ (root, leaf sheath, leaf blade) to this remobilization. Late N amendment allowed a greater N availability of leaf blades and ear N reserves (from 20% up to 26% and from 19% up to 22%, respectively) for remobilization towards the grain, decreasing the root contribution from 28% down to 15%, while the contribution of leaf sheaths was maintained around 35% irrespective of the N applied.

Description: Flooded rice ( Oryza sativa L.) may contain high arsenic (As) concentrations compared to other grain crops. For the development of measures to reduce the As concentration of rice grains, knowledge about the mobility of As within the rice plant is required. Therefore, to investigate the mobilization of As within the plant, rice was grown in nutrient solution and exposed to As either before flowering, after flowering, or continuously until maturity. Furthermore, rice was grown in four soils under greenhouse and field conditions and the time course of As accumulation in grains during the grain-filling period was investigated. When grown in nutrient solution, As removal at flowering did not reduce As concentrations in polished rice compared to plants supplied with As continuously or after flowering. Plants that received As only after flowering had the same As concentrations in shoot and bran as plants receiving As only before flowering. However, continuous As supply resulted in doubling of As concentrations in both plant parts. In contrast to grain and shoot, the As concentration in the root decreased after As removal compared to the treatments receiving As only after flowering or continuously. The observations indicate that As was mobilized from root or shoot to the grain and that it was accumulated in the grain, although it was not available in nutrient solution during the grain-filling period. In soil experiments, the 1000-grain weight increased up to 2 weeks before harvest in the field as well as in the greenhouse. The As concentration in rice grain was constant during the whole grain-filling period. It was at a similar level under field and greenhouse conditions, and its variation among soils was in the same order indicating that soil was the decisive factor for As concentration in grains. Our results suggest that temporary cultural measures during the cultivation period, for example drainage, might be ineffective because of the mobilization capacity within the rice plant. Moreover, harvest before final maturity of grains would not reduce the As concentration since it remained constant during the grain-filling period.

Description: Recent studies indicate that soil soluble organic nitrogen (SON) plays an important regulatory role in the soil–plant N cycle. The aims of this study were to identify the vertical distribution of SON and its correlation with N mineralization, nitrification, and amidohydrolase activities, in a soil repeatedly amended with cow manure or chemical fertilizer. For this purpose, soil samples were collected from 0–20, 20–40, 40–60, 60–80, and 80–100 cm depths of a calcareous soil, which has been annually amended for 5 y with cow manure (CM) at two rates of 50 (CM 50 ) and 100 (CM 100 ) Mg CM ha –1 y –1 . Treatments with chemical fertilizer (CF) and a control (CT) were also included. Soluble organic N, N mineralization, nitrification rates, as well as L-glutaminase and L-asparaginase activities were determined. Both CM 50 and CM 100 enhanced SON content throughout the soil profile. Nitrogen-mineralization rate (N m ) was increased at the 0–20 cm depth of the CM 100 treatment and remained unaffected at the deeper depths. Nitrification rate (N n ) was significantly higher at the 0–60 cm depth of CM 100 compared to CF and CT. L-glutaminase and L-asparaginase activities were significantly increased at the 0–40 cm depth in both CM 50 and CM 100 compared to CF and CT. The amidohydrolase activities could not be detected below 40 cm, regardless of the fertilizer treatments. Our results suggest that SON makes a minor contribution to N mineralization in deep soil layers. It was also concluded that changes in the SON throughout the soil profile were not associated with changes in the N-transformation rates (N m and N n ) and amidohydrolase activities. While we conclude that SON is a major N pool in the whole profile of the manure applied soil further investigation is required to characterize SON and to investigate the bioavailability of SON for microbial activity in different soil depths.

Description: Due to energy crises and stricter environmental regulations, renewable energy sources like bio-methane produced by anaerobic digestion (biogas) become increasingly important. However, the application of slurries produced by biogas fermentation to agricultural land and subsequent ammonia emission may also create environmental risks to the atmosphere and to N-limited ecosystems. Evaluating ammonia loss from agricultural land by model simulation is an important tool of agricultural-systems analysis. The objective of this study was the systematical comparison of ammonia volatilization after application of two types of biogas slurries containing high amounts of energy crops in comparison with conventional animal slurries and to investigate the relative importance of factors affecting the emission process through an empirical model. A high number of ammonia-loss field measurements were carried out in the years 2007/08 in biogas cropping systems in N Germany. The study consisted of simultaneous measurement of NH 3 losses from animal and biogas slurries in multiple-plot field experiments with different N-fertilization levels. The derived empirical model for the calculation of NH 3 losses based on explanatory variables gave good predictions of ammonia emission for both biogas and pig slurries. The root mean square error ( RMSE ) and mean bias error ( MBE ) of the empirical model for validation data were 2.19 kg N ha –1 ( rRMSE 29%) and –1.19 kg N ha –1 , respectively. Biogas slurries produced highest NH 3 emissions compared to the two animal slurries. In view of the explanatory variables included in the model, total NH application rate, slurry type, temperature, precipitation, crop type, and leaf-area index were important for ammonia-volatilization losses.

Description: Soil sulfur (S) partitioning among the various pools and changes in tropical pasture ecosystems remain poorly understood. Our study aimed to investigate the dynamics and distribution of soil S fractions in an 8-year-old signal grass ( Brachiaria decumbens Stapf.) pasture fertilized with nitrogen (N) and S. A factorial combination of two N rates (0 and 600 kg N ha –1 y –1 , as NH 4 NO 3 ) and two S rates (0 and 60 kg S ha –1 y –1 , as gypsum) were applied to signal grass pastures during 2 y. Cattle grazing was controlled during the experimental period. Organic S was the major S pool found in the tropical pasture soil, and represented 97% to 99% of total S content. Among the organic S fractions, residual S was the most abundant (42% to 67% of total S), followed by ester-bonded S (19% to 42%), and C-bonded S (11% to 19%). Plant-available inorganic SO 4 -S concentrations were very low, even for the treatments receiving S fertilizers. Low inorganic SO 4 -S stocks suggest that S losses may play a major role in S dynamics of sandy tropical soils. Nitrogen and S additions affected forage yield, S plant uptake, and organic S fractions in the soil. Among the various soil fractions, residual S showed the greatest changes in response to N and S fertilization. Soil organic S increased in plots fertilized with S following the residual S fraction increment (16.6% to 34.8%). Soils cultivated without N and S fertilization showed a decrease in all soil organic S fractions.

Description: A greenhouse pot experiment was carried out to investigate the effects of different P-fertilizer application forms (triple superphosphate [TSP], compost + TSP, TSP-enriched compost) on the growth of ryegrass and the soil microbial biomass. The fertilizers were applied at equivalent doses for all nutrients to a neutral Luvisol in comparison with an acidic Ferralsol. Fertilizer application led to significantly increased contents of microbial biomass C, N, and P. Furthermore, yields of shoot C and root C, and concentrations of P, Ca, Mg, K, Fe, and Mn in shoots and roots were significantly increased. These increases always followed the order TSP 〈 compost + TSP 〈 TSP-enriched compost. Sole TSP application led only to maximum concentrations of N and S. In the Ferralsol, TSP had only minimal positive effect on the P concentration of the grass shoots. The positive effect of TSP-enriched compost, i.e., incubating TSP together with compost for 24 h, did not differ between the neutral Luvisol and the acidic Ferralsol, i.e., the effect is independent of the soil type. Consequently, soluble inorganic P fertilizer should generally be mixed into an organic fertilizer before application to soil.

Description: The physical properties of a Luvisol derived from loess near Bonn, Germany, under different long-term fertilization treatments were examined. For the investigation of the impact of farmyard manure (FYM) on soil strength at the mesoscale (100 to 300 cm 3 soil cores), undisturbed samples were taken from two different depths (10 and 40 cm), either with no fertilization at all, with full mineral fertilization, with FYM only, and with both mineral and organic fertilization. We investigated hydraulic and mechanical parameters, namely precompression stress, pore-size distribution, saturated hydraulic and air conductivity, and calculated pore connectivity. Long-term organic fertilization resulted in significantly more and coarser pores which in addition were more conductant and mechanically stronger by trend. Mineral fertilization also increased pore volume by trend but not pore functionality. Mechanical strength generally increased with fertilization by trend, however, was reduced again when organic and mineral fertilization were combined. Nonetheless, FYM led to relatively higher soil strength as the FYM-treated plots with lower bulk density attained similar soil strength as the unfertilized but denser plots and thus supported the soil-improving impact of organic amendments. The subsoil physical properties were rather unaffected by fertilization, but were dominated by texture.

Description: Little is known about nutrient fluxes and nutrient-use efficiencies in urban and peri-urban agriculture (UPA) of rapidly expanding cities in developing countries. Therefore, horizontal flows of carbon (C), nitrogen (N), phosphorus (P), and potassium (K) as well as leaching losses of mineral N and P were measured over 2 years in three representative agricultural production systems of Kabul. These comprised 21 gardens and 18 fields dedicated to vegetable farming, cereal farming, and table-grape production (vineyards). Across sites (fields and gardens) biennial inputs averaged 375 kg N ha –1 , 155 kg P ha –1 , 145 kg K ha –1 , and 15 kg C ha –1 while with harvests 305 kg N ha –1 , 40 kg P ha –1 , 330 kg K ha –1 , and 7 kg C ha –1 were removed. In vegetable gardens, biennial net balances were 80 kg N ha –1 , 75 kg P ha –1 , –205 kg K ha –1 , and 4 kg C ha –1 , whereas in cereal farming biennial horizontal balances amounted to –155 kg N ha –1 , 20 kg P ha –1 , –355 kg K ha –1 , and 5 kg C ha –1 . In vineyards, corresponding values were 295 kg N ha –1 , 235 kg P ha –1 , 5 kg K ha –1 , and 3 kg C ha –1 . Annual leaching losses in two selected vegetable gardens varied from 70 to 205 kg N ha –1 and from 5 to 10 kg P ha –1 . Night soil and irrigation water were the major sources among the applied nutrient inputs in all studied farming systems, contributing on average 12% and 25% to total N, 22% and 12% to total P, 41% and 53% to total K, and 79% and 10% to total C, respectively. The results suggest that soils in extensive cereal fields are at risk of N and K depletion and in vegetable gardens of K depletion, while vineyards may be oversupplied with nutrients possibly contributing to groundwater contamination. This merits verification.

Description: Residues from biogas production contain essential plant nutrients such as nitrogen (N), phosphorus (P), and potassium (K) but also organic matter, and should be recycled in crop production. For efficient re-use as fertilizers, the availability of nutrients for crops and the effect of the residues on soil fertility need to be evaluated. Focusing on the element P, we compared effects of codigested slurry with dairy slurry, highly soluble mineral NPK fertilizer, and a control without any P supply (NK). Codigested slurry used in this experiment was based on anaerobic digestion of dairy slurry, maize silage, and wheat grain. The fertilizing effects were tested in an 8-week pot experiment on a sandy and a loamy soil using two crop species ( Zea mays L., Amaranthus cruentus L.). The plant P uptake was up to 64% greater in the slurry treatments than in the treatment without P. The effect of codigested slurry on P uptake was comparable to that of dairy slurry and mineral P. Plant N uptake from codigested slurry was lower than that from mineral N (NK, NPK), but tended to be higher than from dairy slurry. The water-soluble and double lactate–soluble P content of the soil was lower in the slurry treatments than in the mineral-P treatments and accompanied by higher contents of microbial-bound P. Differences between both organic fertilizers were detected for dehydrogenase activity which was up to 32% lower in soils fertilized with codigested slurry than it was in soils fertilized with dairy slurry. Our results indicate that codigestion of slurries in biogas plants does not substantially alter their fertilizer value as P and N sources for crops.

Description: The effect of different deficit-irrigation treatments on the dynamics of mineral nutrients in leaves of peach trees growing under Mediterranean conditions was studied. Treatments consisted of a control, continuous deficit irrigation, regulated deficit irrigation, and partial root drying. The dynamics of nutrients were unchanged by the water deficits, though the amount absorbed was slightly modified. The advantages of deficit-irrigation strategies with regard to water-use efficiency were accompanied by the absence of any harmful effect on leaf mineral nutrition.

Description: It has been suggested that short-term field experiments are not suitable for the quantitative assessment of cropping-systems impact on soil organic matter (SOM) levels in arable soils, as expectable temporal changes are very small compared to a large spatial variation of SOM background levels. However, applying an optimized sampling design based on repeated sampling in small plots, we were able to detect soil total carbon (STC) and nitrogen (STN) changes in the magnitude of ≈ 1% (STC) and ≈ 2% (STN) of background levels with only four replications, respectively. Gradually enlarging the sample size up to n = 24 did not considerably improve change detectability with STC, but with STN ( n = 15 allowing for the dection of ≈ 1% change of background levels). The common calculation of minimum detectable differences (MDD) based on a state analysis of SOM levels instead of repeated measurements considerably underestimated change detectability.

Description: Two experiments were conducted to study the effect of grafting on nitrogen-use efficiency (NUE) in mini-watermelon plants. In the first study, mini-watermelon plants ( Citrullus lanatus [Thumb.] Matsum. and Nakai cv. Minirossa) either ungrafted or grafted onto Macis, Vita ( Lagenaria siceraria [Mol.] Standl.), PS1313, and RP15 ( Cucurbita maxima Duchesne × Cucurbita moschata Duchesne) rootstocks grown in hydroponics were compared in terms of shoot dry biomass, leaf area, root-to-shoot ratio, SPAD index, shoot N uptake, and nitrate reductase (NR) activity 40 d after transplantation in response to nitrate concentration in the nutrient solution (0.5, 2.5, 5, 10, 15, or 20 mM of NO ). In the second experiment, the suitability of a selected rootstock with high NUE (Vita) to improve crop performance and NUE of grafted mini-watermelon plants was evaluated under field conditions. In the hydroponic experiment mini-watermelon grafted onto Vita rootstock needed the lowest nitrate concentration (1.31 mM of NO 3 ) in the nutrient solution to reach half maximum shoot dry weight. Total leaf area, SPAD index, and shoot N uptake increased in response to an increase of N concentration in the nutrient solution. At 2.5 mM NO , mini-watermelon grafted on either Vita or RP15 had the highest NR activity whereas no significant difference was observed at 10 mM NO . The open-field study indicated that increasing N-fertilization rates from 0 to 100 kg ha –1 improved total and marketable yields of mini-watermelon plants while decreasing NUE. When averaged over N levels, the marketable yield, NUE, N-uptake efficiency, and N-utilization efficiency were significantly higher by 39%, 38%, 21%, and 17%, respectively, in Minirossa grafted onto Vita compared to ungrafted Minirossa plants. Therefore, grafting mini-watermelon plants onto selected rootstocks can be used as a quick and effective method for improving productivity and NUE.

Description: An evaluation of the factors determining the occurrence and the properties of soils with low permeability occurring in vast areas in S Portugal was carried out taking into account the terrain morphology and the geology of the region. This paper deals with the variation patterns of the physical and chemical characteristics of soils from several soil toposequences that occur under different gradient slopes and on different parent rocks. Spatial variation of soil properties mainly depends on the composition of their cation-exchange complex, as the role of other factors, such as the mineralogy of the clay fraction, were of minor importance. There is often a stronger increment of Na and/or Mg than of Ca with depth, causing a variable degree of sodicity in some of these soils, to which waterlogging tendency of their upper horizons is related. Though the occurrence of these features is determined by the nature of the parent rock, their degree of expression varies primarily according to the topographic position of soils. Therefore, a catenary distribution including nonsodic Cambisols or Luvisols in the hillcrests and Stagnic Solonetz or Sodic Luvisols or Sodic Stagnosols in the topographic lows is common. Such soil characteristics are of utmost importance for irrigation suitability and management of these soils, and for environmental impacts assessment, as the region is vulnerable to desertification.

Description: Oxisols cover ≈ 23% of the land surface in the tropics and are utilized extensively for agricultural purposes in the tropical countries. Under the variable input types of agricultural systems practiced locally, some of these soils still appear to have problems in terms of proper soil classification and subsequently hinder attempts to implement sustainable agro-management protocols. The definition for Oxisols in Soil Survey Staff (1999) indicates that additional input is still required to refine the definition in order to resolve some of the outstanding classification problems. Therefore, the objective of this study is to examine the properties of some Oxisols and closely related soils in order to evaluate the classification of these soils. Soils from Brazil, several countries in Africa, and Malaysia were used in this study. Field observations provided the first indication that some of the presently classified kandi-Alfisols and kandi-Ultisols were closer to Oxisols in terms of their properties. Water-retention differences and apparent CEC of the subsurface horizons also supported this idea. The types of extractable Fe oxides and external specific surface areas of the clay fractions showed that many kandic horizons have surface properties that are similar to the oxic horizons. Micromorphology indicated that the genetic transition from the argillic to the oxic involves a diminishing expression of the argillic. Properties, such as CEC, become dominant. The kandic horizon is therefore inferred as a transition to the oxic horizon. It is proposed that the Oxisols be keyed out based only on the presence of an oxic horizon and an iso–soil temperature regime. The presence of a kandic horizon will be reflected at lower levels in Oxisols. The Oxisols will now be exclusive to the intertropical belt with an iso–soil temperature regime. The geographic extend of the Oxisols would increase and that of kandi-Alfisols and Ultisols would decrease. A few kandi-Alfisols and Ultisols in the intertropical area will have low CEC which would fail the weatherable mineral contents. The kandic subgroups of some Alfisols and Ultisols will be transitional between the low (〈 16 cmol c [kg clay] –1 )- and high (〉 24 cmol c [kg clay] –1 )-activity clay soils. The proposed changes to classification will contribute to a better differentiation of the landscape units in the field. Testing of the proposed classification on some Malaysian soils showed that the new definition for Oxisols provides a better basis for the classification of the local soils and the development of meaningful soil-management groups for plantations.

Description: Variability in soil properties is a complication for fertilization, irrigation, and amendment application. However, only limited progress has been made in managing soil variability for uniform productivity and increased water-use efficiency. This study was designed to ameliorate the poor-productivity areas of the variable sandy soils in Florida citrus groves by using frequent small irrigations and applying organic and inorganic soil amendments. Two greenhouse experiments were set up with sorghum and radish as bioassay crops in a randomized complete block design (RCBD). The factors studied were two soil-productivity classes (very poor and very good), two water contents (50% and 100% of field capacity), two amendments (phosphatic clay and Fe humate), and two amendment rates (10 and 25 g kg –1 for sorghum and 50 and 100 g kg –1 for radish). Amendments applied at 50 and 100 g kg –1 increased the water-holding capacity (WHC) of poor soil by 2- to 6-fold, respectively. The lower rates (10 and 25 g kg –1 ) of amendments were not effective in enhancing sorghum growth. The higher rates (50 and 100 g kg –1 ) doubled the radish growth as compared to the control. The results indicate that rates greater than 50 g kg –1 of both amendments were effective in improving water retention and increasing productivity. Irrigation treatment of 100% of field capacity (FC) increased the sorghum and radish growth by about 2-fold as compared with the 50%–water content treatment. The results suggest that the root-zone water content should be maintained near FC by frequent small irrigations to enhance water availability in excessively drained sandy soils. In addition, application of soil amendments in the root zone can enhance the water retention of these soils. Furthermore, managing variable sandy soils with WHC-based irrigation can increase water uptake and crop production in the poor areas of the grove.

Description: A greenhouse experiment was conducted to evaluate the effects of humic substances extracted from composted sewage sludge on growth, phenological development, and photosynthetic activity of pepper ( Capsicum annuum L. cv. Piquillo) plants. Humic substances derived from composted sludge (HSS) were compared with those derived from leonardite (HSL). Two doses of both humic substances were assayed (200 and 500 mg C [L substrate] –1 ) and compared with a control (C). HSS showed higher nitrogen content and a higher percentage of aliphatic carbon, as well as a lower content of aromatic and phenolic carbon than HSL. HSS significantly increased plant dry-matter production (up to 560%), plant height (86%–151%), and leaf area (436%–1397%) during the early stages of pepper development. Net photosynthesis and stomatal conductance increased in the treatments with HSS (up to 48% and 63%, respectively) at the vegetative stage. In addition, HSS accelerated the phenological development of pepper plants, reducing significantly the number of days to flowering and ripening, which occurred 12 and 14 d earlier than in control plants, respectively. In general, the treatments with HSS and HSL did not markedly affect chlorophyll and nutrient concentrations in the leaves. At maturity, only small differences in total fruit yield, number of fruits per plant, and fruit size were observed between amended and control plants. The results suggest that the mechanisms through which HSS affected plant growth and development were not associated with an improved nutrient uptake. Although the identity of the growth-promoting factors remains to be found, the results suggest that they may be linked to the chemical structure of the humic substances.

Description: An accurate assessment of soil respiration is critical for understanding and predicting ecosystem responses to anthropogenic perturbation such as climate change, pollution, and agriculture. Infra-red gas analyzer (IRGA)–based field measurement is the most widely used technique for assessing soil-respiration flux rates. In this study, respiration rates obtained with two common IRGA systems (LI-COR 8100 and PP Systems EGM-4) were compared across three ecosystem types. Our results showed that both methods were highly comparable in their flux estimates, but the associated methodology used (notably the use or absence of a soil collar) resulted in greater uncertainty in flux rates and a greater degree of intrasite variation. Specifically, the use of collars significantly decreased the flux estimate for both IRGAs compared to the no-collar estimate. The disturbance caused by collar insertion was assumed to be a major factor in causing the differing flux estimates, with root and mycorrhizal severance likely being the main contributor. We conclude that the two IRGAs used in this study can be reliably compared for overall flux estimates but emphasis is needed to validate a common measurement methodology.

Description: Provision of appropriate fertilizer recommendations to smallholder farmers is becoming increasingly important, for reasons of food security, economic viability, and the need to maintain soil fertility. Oil palm is one of the most important crops in the humid tropics, but smallholder growers (〈 10 ha) typically have low yields, largely due to inadequate fertilizer inputs and/or incomplete harvesting. It is difficult to produce appropriate fertilizer recommendations for the smallholder growers, due to their large numbers and small farm sizes. In this work, we developed a way of transferring to smallholder growers the fertilizer recommendations that have been developed for nearby plantation fields using large fertilizer trials. The study site was in West New Britain Province, Papua New Guinea, and transfer of information was done using a geographic information system and maps of plantation fields, smallholder blocks, and soil types. The soil-map-unit descriptions were interpreted, and a unified classification system was derived. Then, fertilizer recommendations that had been made on a field-specific basis for the large plantations were allocated to soil types and thereby to individual smallholder blocks. In this way, block-specific fertilizer recommendations were made for more than 4000 individual smallholders. The procedures used were developed into a conceptual framework which is transferable to other regions. Recommendations can be updated as new information becomes available on smallholder block locations or plantation fertilizer recommendations.

Description: The efficacy of arbuscular mycorrhizae (AM) on nutrients, organic solutes, and antioxidant enzymes of wheat under salt stress was investigated and related to root colonization and plant productivity. The mycorrhizal inoculation increased N, P, K, Ca, and Mg uptake, soluble sugars, free amino acids, and proline accumulation, as well as peroxidase and catalase activities under saline conditions as compared to nonmycorrhizal plants. On the other hand, Na concentration was lower in mycorrhizal than in nonmycorrhizal plants grown under saline conditions. Arbuscular mycorrhizae protected wheat against the detrimental effects of salinity and stimulated its productivity. Hence, mycorrhizal colonization can play a vital role in the mitigation of the adverse effects of salinity by improving the wheat osmotic adjustment response, enhancing its defense system, and alleviating oxidative damage to cells. Arbuscular mycorrhizae are able to alter plant physiology in a way that empowers the plant to grow more efficiently on salt-affected lands.

Description: Different procedures to investigate dissolved trace element concentration at the transition from unsaturated to saturated zone in soils were compared by concurrent sampling of soil solution and solid soil material in this zone. The in situ sampled soil solution from the percolated water was used to measure in situ concentrations, while solid soil material was used to measure concentrations at two liquid–solid ratios using batch experiments on 250 sample pairs. The liquid–solid ratios were 2 L kg –1 and 5 L kg –1 . At 5 L kg –1 , the ionic strength was adjusted with Ca(NO 3 ) 2 to a sample-specific value similar to in situ , while at 2 L kg –1 , the ionic strength was not adjusted. The extracted concentrations of most trace elements exhibited a statistically significant but weak correlation ( p value 〈 0.01) to the corresponding in situ concentrations. In the liquid–solid ratio of 2 L kg –1 extracts, Pb and Cr showed very poor comparability with the in situ equivalent. A likely cause was the enhanced dissolved-organic-C release in the extract due to the lower ionic strength compared to in situ conditions in combination with effects from drying and moistening soil samples. For the other elements, correlation increased in the order As 〈 Cu, Zn, Sb, Mo, V 〈 Cd, Ni, Co where adjustment of the ionic strength led to slightly better results. In addition to the element-specific shortcomings, it appeared that low concentration levels of in situ concentrations were generally underestimated by batch extraction methods. The liquid–solid ratio of 2 L kg –1 extracts could only be used as a method to predict exceedance of thresholds if a safety margin of approximately one order of magnitude higher than the thresholds was adopted. The ability of the batch-extraction methods to estimate in situ concentrations was equally limited.

Description: Tonoplast Na + /H + antiporters increase the salt resistance of various plant species, but very little is known about the role of these antiporters in the salt resistance of trees. Understanding the physiological responses of plants to salinity stress is of paramount importance in examining the salt resistance of transgenic plants. In this study, the wild-type poplar (WT; Populus × euramericana var. Neva) and its transgenic varieties (TR) that overexpress the AtNHX1 gene were exposed to various seawater concentrations (0%, 10%, 20%, and 30%) for 30 d to determine the effects of seawater on seedling growth, ion content, and photosynthetic productivity. Results show that TR plants grew much better than WT under saline conditions. Differences between WT and TR in most parameters were significant after 30 d exposure to 20% and 30% seawater concentrations. The dry weight of TR was higher than that of WT for each seawater treatment. Transgenic variety was able to maintain higher photosynthetic ability than WT upon exposure to salinity and maintained higher K + concentrations and K + : Na + ratio but had less Cl – compared with WT. This suggests that AtNHX1 has a critical role in the regulation of K + homeostasis, which in turn affects plant K + nutrition and salt resistance.

Description: Recent studies have documented adverse affects of urea on the establishment and growth of aerobic rice when applied at seeding. The following experiments were conducted to examine the relative importance of ammonia and nitrite (NO ) toxicities as mechanisms contributing to poor germination and early growth of aerobic rice. Soil was collected from an experiment in the Philippines where aerobic rice was grown continuously for 7 years. Subsamples of the soil were: (1) pretreated with sulfuric acid (0.5 M H 2 SO 4 added at 75 mL kg –1 ), (2) oven-heated at 120°C for 12 h, or (3) left untreated. In a greenhouse study N was applied to the untreated, acidified, and oven-heated soils as either urea or ammonium sulfate (0.0 or 0.3 g N kg –1 ). Plant height, root length, total biomass, and number of seminal roots were evaluated after 10 d. Microdiffusion incubations were used to assess the effects of soil pretreatment, N source, and N rate (0, 0.5, 1.0, 1.5 g N kg –1 ) on ammonia (NH 3 ) volatilization and germination. Nitrite incubations were conducted to establish a critical level for NO toxicity and measure the extractable NO and germination trends as affected by soil pretreatment, N source, and N rate. On untreated soil, urea reduced early growth and germination while ammonium sulfate caused no adverse effects. Progressively higher rates of urea increased NH 3 volatilization and inhibited germination, while oven-heating and acidification minimized the adverse effects. All treatment combinations (soil pretreatment, N source, N rate) had extractable NO levels below the critical level of 0.2 g N kg –1 , suggesting that ammonia and not NO toxicity was the principal cause of inhibition. Since the risk of NH 3 toxicity is highest just following urea hydrolysis, strategies to optimize the timing and placement of urea should be considered.

Description: Soil structure affects all soil functions especially those related to physical and biological processes. On the other hand, soil structure itself is directly affected by these agents. Hence, soil structure—from single pores to the pedon scale—is expected to reflect the capacity of soil to deliver ecosystem functions. We analyzed soil structure including its seasonal dynamics for two plots within the long-term fertilization experiment in Bad Lauchstädt (Germany). The different plots received very different amounts of mineral and organic fertilizers over a period of 106 y. The quantification of structural properties includes pore-size distribution and pore connectivity obtained by X-ray microtomography. We present a methodological approach for image analysis that allows to combine samples of different size and resolution to cover pores within one order of magnitude in diameter. The results for the different plots obtained in spring and summer are compared. We found that the enormous difference in energy input only affects the structure of the topsoil (Ap horizon) towards a higher porosity and pore-network connectivity and in terms of an increased resilience after tillage. However, the structural properties of the subsoil below the plowed horizon (Ah horizon) are not affected. We hypothesize that the structure of the subsoil reflects soil formation over much longer time scales, it allows for an increased turnover of soil organic matter, and it is rather stable at the time scale of the fertilization experiment.

Description: The organic matter supply can promote the dispersal and activity of applied plant growth–promoting rhizobacteria (PGPR), but the complementary effect of organic fertilization and PGPR application on the turnover of P is scarcely known. The effects of the application of two PGPR strains ( Pseudomonas fluorescens strain DR54 and Enterobacter radicincitans sp. nov. strain DSM 16656) alone and in combination with organic fertilization (cattle manure and biowaste compost) on growth and P uptake of maize ( Zea mays L.) and oilseed rape ( Brassica napus L.) were investigated under semi–field conditions. Furthermore, P pools and phosphatase activities in soil and the arbuscular mycorrhizal–fungi colonization of maize roots were examined. The organic-fertilizer amendments increased the growth and P uptake of both plant species and the soil P pools. The application of the E. radicincitans strain increased P uptake of oilseed rape when no organic fertilizer was added. Furthermore, the application of both bacterial strains increased the activities of phosphatases under both plant species. Here, the effect of the PGPR application even exceeded the effect of organic fertilization. The magnitude of this effect varied between the different fertilizing treatments and between the two bacterial strains. Phosphatase activities were increased to the greatest extent after application of P. fluorescens in the unfertilized soil. Under rape increases of 52% for acid phosphatase activities (ACP), 103% for alkaline phosphatase activities (ALP), and 133% for phosphodiesterase (PDE) were observed therewith. In the unfertilized soil, the application of P. fluorescens also resulted in a strong increase of the arbuscular mycorrhizal colonization of maize. We conclude that application of PGPR can promote the P mobilization and supply of crops in P-deficient soils, however, in combination with organic fertilization these effects might be masked by a general improved P supply of the crops. Interactive effects of applied bacterial strains and organic fertilization depend on the sort of organic fertilizer and crop species used.

Description: To ensure high yield and quality in organic vegetable production, crops often require additional fertilizer applied during the season. Due to the risk of contamination of edible plant products from slurry, plant-based fertilizers may be used as an alternative. The purpose of our work was to develop mobile green manures with specific high nutrient concentrations ( e.g., nitrogen [N], sulfur [S], and phosphorus [P]) that are released quickly after soil incorporation and that are easy to handle during storage and application. To distinguish from traditional green manures that are grown to improve soil fertility, the term “mobile green manures” is used for green-manure crops that are harvested in one field and then moved as a whole and used as fertilizer in other fields. To further investigate mobile-green-manure crops for use as efficient fertilizers, pot and field experiments were conducted with cauliflower ( Brassica oleracea botrytis ) and kale ( Brassica oleracea sabellica ) supplied with organic matter consisting of a wide range of plant species with varying nutrient concentrations. Further, field experiments were conducted with leek ( Allium porrum ) and celery ( Apium graveolens dulce ) supplied with increasing amounts of organic matter consisting of fresh, ensiled, or dried green manures. Results show that garden sorrel ( Rumex acetosa ), dyer's woad ( Isatis tinctoria ), and fodder radish ( Raphanus sativus ) harvested with a high leaf-to-stem ratio resulted in high P concentration, and cruciferous crops in high S concentration. Dyer's woad, salad burnet ( Sanguisorba minor ), and stinging nettle ( Urtica dioica ) showed high boron (B) concentration, whereas species such as dandelion ( Taraxacum officinale ), chicory ( Cichorium intybus ), and garden sorrel showed high potassium (K) concentration. Green manures with high P and S concentrations increased the nutrient uptake and yield of pot-grown cauliflower and kale. Field experiments showed that the production of cauliflower and kale decreased when the carbon-to-nitrogen (C : N) ratio of applied green manure increased. In kale, for example, application of 160 kg N ha –1 in early harvested lucerne ( Medicago sativa ) with a C : N ratio of 10 resulted in the highest kale production whereas application of an equal amount of N in late harvested lucerne with a C : N ratio of 20 produced 34% less. Differences in vegetable production were not due to the amount of N applied, but to the N availability. Field experiments with fresh, ensiled, or dry green manure applied to leek and celery showed that the C : N ratio has to be low to get a fast response. Further, these field experiments demonstrate the importance of green manures, which can be stored and are easy to handle during transport, crop application, and soil incorporation. It is concluded that it is possible to produce green manures with high concentrations of S, P, K, and B, and low C : N ratios and that these properties have a great impact on the value of the green manure for vegetable production.

Description: Splash cups have long been successfully used for both the quantification of kinetic energy of rainfall and the detachability of soil particles by rainfall impact, the so-called “splash erosion”. Measurements of kinetic energy, however, have been difficult to operate in the field especially in remote areas, on steep slopes, and in forests since boundary conditions need to be controlled precisely. This paper introduces a new splash cup based on Ellison's archetype that reliably and accurately measures kinetic energy as a function of sand loss under a large variety of conditions. The Tübingen splash cup (T splash cup) is relatively easy to operate under harsh field conditions, and it can be used in experimental designs with a large number of plots and replications at reasonably low costs. The cup is constructed from plastic laboratory flasks and plastic pipes from water-supply equipments. The unit sand is held by a removable carrier system that can easily be replaced in the field. The splash cups have been calibrated in combination with a laser distrometer using a linear regression function with r 2 = 0.98. They measure kinetic energy over a wide range of rainfall intensities from 0.6 to 40 L m –2 h –1 . Kinetic energy per area varies between 10 and 250 J m –2 . Two years of field test measurements in a subtropical forest ecosystem in China proved the reliability, durability, and usability of our new splash cups and allowed detecting differences in kinetic energy between different tree species and biodiversity levels.

Description: A multivariate statistical approach based on a large data set of abiotic and biotic variables was used to classify four contrasting-land-use soils. Soil samples were collected at increasing depth from a calcareous agricultural soil, a temperate upland grassland soil, a moderately acidic agricultural soil, and an acidic pine forest soil. Analytical investigations were carried out by using a combination of conventional physical, chemical, and biochemical methods coupled with denaturing gradient gel electrophoresis (DGGE) community fingerprinting of PCR-amplified 16S rRNA gene-coding fragments from soil-extracted total-community DNA. The data set of soil physical, chemical, and biochemical variables was reduced in dimensionality by means of a principal-component-analysis (PCA) procedure. Compositional shifts in soil bacterial-community structure were analyzed through a clustering algorithm that allowed identifying six main bacterial-community clusters. DGGE fingerprinting clusters were further analyzed by discriminant analysis (DA) using extracted PCA components as explanatory variables. Soil organic matter–related pools (TOC, TN) and functionally related active pools (microbial biomass C and N, K 2 SO 4 -extractable C) significantly decreased with soil depth, and resulted statistically linked to one other and positively related to enzymatic activities (acid phosphatase, arylsulfatase, β-glucosidase, dehydrogenase, hydrolysis of fluorescein diacetate) and silt content. Besides organic-C gradients, pedogenetic-driven physico-chemical properties, and possibly soil thermal and moisture regimes seemed to play a key role in regulating size and energetic ecophysiological status of soil microbial communities. DGGE analysis showed that contrasting horizons were conducive to the dominance of particular bacterial ribotypes. DA revealed that the bacterial-community structure was mainly influenced by organic matter–related variables (TOC, TN, CEC, C flush , N flush , Extr-C), chemical properties such as pH, CaCO 3 , and EC, together with textural properties. Results indicate that, beyond land use or plant cover, pedogenetic-driven physico-chemical conditions changing with soil type and depth are the key factors regulating microbial size and activity, and determining the genetic structure of bacterial community.

Description: Sulfonamides are the second most used antibiotic class in veterinary medicine and applied to livestock to treat bacterial infections. Subsequently, they are spread onto agricultural soils together with the contaminated manure used as fertilizer. Both manure and antibiotics affect the soil microbial community. However, the influence of different liquid manure loads on effects of antibiotics to soil microorganisms is not well understood. Therefore, we performed a microcosm experiment for up to 32 d to clarify whether the function and structure of the soil microbial community is differently affected by interactions of manure and the antibiotic sulfadiazine (SDZ). To this end selected concentrations of pig liquid manure (0, 20, 40, 80 g kg –1 ) and SDZ (0, 10, 100 mg kg –1 ) were combined. We hypothesized that incremental manure amendment might reduce the effect of SDZ in soils, due to an increasing sorption capacity of SDZ to organic compounds. Clear dose-dependent effects of SDZ on microbial biomass and PLFA pattern were determined, and SDZ effects interacted with the liquid manure application rate. Soil microbial biomass increased with incremental liquid manure addition, whereas this effect was absent in the presence of additional SDZ. However, activities of enzymes such as urease and protease were only slightly affected and basal respiration was not affected by SDZ application, while differences mostly depended on the concentration of liquid manure. These results illustrated that the microbial biomass and structural composition react more sensitive to SDZ contamination than functional processes. Furthermore, effects disproportionally increased with incremental liquid manure addition, although extractable amounts of SDZ declined with increasing liquid manure application.

Description: The present investigation was aimed to analyze influence of earthworm culture on nutritive status, microbial population, and enzymatic activities of composts prepared by utilizing different plant wastes. Vermicomposts were prepared from different types of leaves litter of horticulture and forest plant species by modified vermicomposting process at a farm unit. Initial thermophilic decomposition of waste load using cow-dung slurry was done in the separate beds. The culture of Eisenia fetida was used for vermicomposting in specially designed vermibeds at the farm unit. The physico-chemical characteristics, enzyme activities (oxido-reductases and hydrolases), and microbial population (bacteria, fungi, free-living nitrogen-fixing bacteria, actinomycetes, Bacillus, Pseudomonas , phosphate-solubilizing bacteria and fungi) of vermicomposts were found significantly higher ( p 〈 0.05) than those of control (without earthworm inoculum). The study quantified significant contributions of earthworm culture to physico-chemical, enzymatic, and microbiological properties of vermicompost and confirmed superior fertilization potential of vermicompost for organic farming. The agronomic utility of vermicompost was assessed on yellow mustard plant in a pot experiment. Pot soil was amended with different ratios (5%, 10%, 20%) of vermicompost and normal compost (without earthworm inoculum). Effects of these amendments on the growth of Brassica comprestis L. were studied. The significant differences ( p 〈 0.05) in the growth of plant were observed among vermicompost-, compost-amended soil, and control. Vermicompost increased the root and shoot lengths, numbers of branches and leaves per plant, fresh and dry weights per plant, numbers of pods and flowers, and biochemical properties of plant leaf significantly, especially in 20% amendment. These results proved better fertilization potential of vermicompost over non-earthworm-inoculated compost.

Description: Experiments to evaluate the effect of in-season calcium (Ca) sprays on late-season peach ( Prunus persica L. Batsch cv. Calrico) were carried out for a 2-year period. Calcium formulations (0.5% and 1.0% in 2008 and only 0.5% tested in 2009) supplied either as CaCl 2 or Ca propionate in combination with two or three adjuvants (0.05% of the nonionic surfactants Tween 20 and Break Thru, and 0.5% carboxymethylcellulose, CMC) were sprayed four to five times over the growing season. Peach mesocarp and endocarp Ca concentrations were determined on a 15-day basis from the beginning of May until the end of June. Further tissue analyses were performed at harvest. A decreasing trend in fruit Ca concentrations over the growing season was always observed regardless of the Ca treatments. Both in 2008 and 2009, significant tissue Ca increments associated with the application of Ca-containing sprays in combination with adjuvants were only observed in June, which may be coincident with the period of pit hardening. In 2008, both at harvest and after cold storage, the total soluble-solids concentration (° Brix) of fruits supplied with Ca propionate (0.5% and 1.0% Ca) was always lower as compared to the rest of treatments. The application of multiple Ca-containing sprays increased firmness at harvest and after cold storage, especially when CaCl 2 was the active ingredient used. Supplying the adjuvants Tween 20 and CMC increased fruit acidity both at harvest and after cold storage. Evaluation of the development of physiological disorders after cold storage (2 weeks at 0°C) indicated a lower susceptibility of Ca-treated fruits to internal browning. Fruits treated with multiple CaCl 2 -, CMC-, and Break Thru®-containing sprays during the growing season were significantly less prone to the development of chilling injuries as compared to untreated peaches.

Description: Recent literature confirmed that P fractions in soil are controlled by land use. However, differences in intensity of the same type of land use have received less attention although management intensity plays a crucial role in determining nutrient supply in soil. The objective of our work was to assess the influence of land-use intensity (LUI) on P fractions in soil. In the “Biodiversity Exploratories”, grassland and forest sites in Germany were selected in three regions (Schorfheide-Chorin, Hainich-Dün, Schwäbische Alb). In spring 2008, we sampled topsoil of 241 experimental plots. The plots included unfertilized and fertilized meadows, pastures, and mown pastures and near-natural to intensively used forests. Land-use intensity was classified according to the extent of annual biomass removal. We used the sequential extraction method of Hedley et al. (1982) to characterize P partitioning in soil. In summary, total P (TP) concentrations in soil were lowest at Schorfheide-Chorin (62–952 mg kg –1 ) followed by the Hainich-Dün (230–1631 mg kg –1 ) and the Schwäbische Alb (205–1838 mg kg –1 ). Differences between grassland and forest sites were mainly attributable to pH. The pH value was the most important factor among several soil properties explaining P partitioning in soil. For grassland, at pH values ≈ 6.5, the application of lime-containing fertilizer increased P availability in soil while effects of organic or mineral P fertilizers were negligible and related to the low application rates (〈 12 kg ha –1 ). Land-use intensity contributed up to 10% of the variation in the contribution of NaOH-P i to TP concentrations (ANOVA, Type I). In the Schwäbische Alb grassland soils, elevated LUI resulted in low NaOH-P i concentrations in soil which was probably caused by reduced sorption. Our findings highlight the importance of LUI as a control of P fractions in soil.

Description: This study explored the influence of 10 annual forage legumes belonging to the Lathyrus and Vicia genera on wet aggregate stability (WAS) and dispersion ratio (DR) indices of a clay soil. Five Lathyrus and five Vicia species were sown in autumn. Seed-to-seed and row-to-row distance was maintained at 5 cm and 20 cm, respectively. The experiment was planned in a randomized block design with three replications. After 90 d following seed harvest, soil cores were collected from two depths (0–15, 15–30 cm) in each plot and WAS and DR were determined. Annual forage legumes increased WAS of the soil but decreased the DR index. The WAS and DR values were affected at level of p 〈 0.001 by genus, species, and soil depth. Values of WAS and DR of the control plots without plant on the average were found to be 44.5% and 9.3% for 0–15 cm, and 41.2% and 10.1% for 15–30 cm, respectively. For 0–15 cm depth, the highest WAS (77.7%) and the lowest DR (6.4%) values were found in L. sphaericus L. (wild) plots. For 15–30 cm depth, the highest WAS value (62.6%) was obtained in L. annuus L. (wild) plots and the lowest DR value (6.7%) was in L. sativus L. (Gurbuz-2001) plots.

Description: A major challenge in sustainable crop management is to ensure adequate P supply for crops, while minimizing losses of P that could negatively impact water quality. The objective of the present study was to investigate the effects of long-term applications of different levels of mineral fertilizers and farmyard manure on (1) the availability of P, (2) the relationship between soil C, N, and P, and (3) the distribution of inorganic and organic P in size fractions obtained by wet sieving. Soil samples were taken from the top 20 cm of a long-term (29 y) fertilization trial on a sandy Cambisol near Darmstadt, SW Germany. Plant-available P, determined with the CAL method, was little affected by fertilization treatment ( p 〈 0.05) and was low to optimal. The concentration of inorganic and organic P extracted with a NaOH-EDTA solution (P NaOH-EDTA ) averaged about 350 mg (kg dry soil) –1 , with 42% being in the organic form (P o ). Manure application tended to increase soil C, N, and P o concentrations by 8%, 9%, and 5.6%, respectively. Across all treatments, the C : N : P o ratio was 100 : 9.5 : 2 and was not significantly affected by the fertilization treatments. Aggregate formation was weak due to the low clay and organic-matter content of the soil, and the fractions 〉 53 μm consisted predominantly of sand grains. The different fertilization treatments had little effect on the distribution of size fractions and their C, N, and P contents. In the fractions 〉 53 μm, P NaOH-EDTA ranged between 200 and 300 mg kg –1 , while it reached 1260 mg kg –1 in the fraction 〈 53 μm. Less than one third of P NaOH-EDTA was present as P o in the fractions 〉 53 μm, while P o accounted for 70% of P NaOH-EDTA in the smallest fraction (〈 53 μm). Therefore, 16% and 28% of P NaOH-EDTA and P o , respectively, were associated with the smallest fraction, even though this fraction accounted for 〈 5% of the soil mass. Therefore, runoff may cause higher P losses than the soil P content suggests in this sandy soil with a weak aggregate formation. Overall, the results indicate that manure and mineral fertilizer had similar effects on soil P fractions.

Description: The aim of this study was to evaluate the interaction between yield levels of nonleguminous crops and soil organic matter (SOM) under the specific conditions of organic and conventional farming, respectively, and to identify implications for SOM management in arable farming considering the farming system (organic vs. conventional). For that purpose, correlations between yield levels of nonlegume crops and actual SOM level (C org , N t , C hwe , N hwe ) as well as SOM-level development were examined including primary data from selected treatments of seven long-term field experiments in Germany and Switzerland. Yield levels of nonlegume crops were positively correlated with SOM levels, but the correlation was significant only under conditions of organic farming, and not with conventional farming treatments. While absolute SOM levels had a positive impact on yield levels of nonlegumes, the yield levels of nonlegumes and SOM-level development over time correlated negatively. Due to an increased demand of N from SOM mineralization, higher yield levels of nonlegumes obviously indicate an increased demand for OM supply to maintain SOM levels. Since this observation is highly significant for farming without mineral-N fertilization but not for farming with such fertilization, we conclude that the demand of SOM-level maintenance or enhancement and thus adequate SOM management is highly relevant for crop production in organic farming both from an agronomical and ecological point of view. Under conventional management, the agronomic relevance of SOM with regard to nutrient supply is much lower than under organic management. However, it has to be considered that we excluded other possible benefits of SOM in our survey that may be highly relevant for conventional farming as well.

Description: Maize ( Zea mays L.) is an important crop in central Thailand where fallow is widely practiced and farmers are interested in crop rotation and beneficial soil biota. A pot experiment using a Typic Paleustult (topsoil + subsoil) from the National Corn and Sorghum Research Centre, Nakhonratchasima Province, Thailand was undertaken over three successive crops to evaluate effects of agronomic practices on populations of arbuscular mycorrhizal (AM) fungi and to determine whether reintroduction of a local Glomus was beneficial to maintain maize yield. The three crops and their treatments were: (1) preceding crop: maize grown in all pots; (2) subexperiment 1: agronomic practices [maize, fallow ± soil disturbance, fallow with solarization, non–AM host (cabbage)]; and (3) subexperiment 2: maize ± Glomus sp. 3 at three rates of P fertilization (0, 33, 92 kg P ha –1 ). The AM-fungal community was established under the preceding crop. In subexperiment 1, the three fallow treatments decreased (30%–40%) the total AM spore number in the topsoil whereas there was no change under maize or cabbage. Glomus , the dominant genus, showed sensitivity to fallow. In subexperiment 2, inoculation with Glomus sp. 3 enhanced total AM spore number and root colonization when applied following the three fallow treatments. Furthermore, inoculation promoted grain yield; at nil P following fallow ± soil disturbance, at 33 kg P ha –1 following fallow without soil disturbance, and following solarization. Two treatments, maize following maize and maize following cabbage, did not respond to inoculation with Glomus sp. 3. Overall, the results suggest that reintroduction of Glomus sp. 3, a local AM fungus in this soil, may overcome negative effects of fallow and promote effectiveness of P fertilizer. Further work is needed to evaluate the benefits of other indigenous AM species that persist under modern fertilization practices.

Description: A few studies have shown that amine compounds ( e.g., hydroxylamine) can be co-metabolically introduced into the reaction pathway of denitrification. During this microbial process, the N atom of the amine species is bound to a N atom of nitrite. In case of hydroxylamine, this concomitant reaction ultimately results in the formation of hybrid N 2 O. Due to its co-metabolic character the process has been termed co-denitrification. Hybrid N 2 O production during co-denitrification has been proven to occur in prokaryotic ( e.g., Pseudomonas sp. ) as well as eukaryotic ( e.g., Fusarium sp. ) species. Many of them are already well-known as common denitrifiers. However, until now no clear evidence has been provided to show that N 2 O production by co-denitrification really takes place in a soil. In the present study, a formation of hybrid N 2 O was revealed by an adapted 15 N-tracer model, when both hydroxylamine and 15 N-nitrate were applied (mol ratio 10:1) to an anaerobically incubated soil suspension from a Haplic Chernozem. The presence of hybrid N 2 O was also indicated by a novel characteristic factor ( R binom ) developed for a hybrid-N-N-gas detection. By contrast, no hybrid N 2 O was found when either an autoclaved soil suspension, only nitrate or only hydroxylamine was used. Thus, it appears that hybrid-N 2 O formation occurred due to co-denitrification of hydroxylamine. Hence, this is the first study which demonstrates hybrid-N 2 O production by co-denitrification beyond a microbial species level. The 15 N-tracer model revealed that under the given experimental conditions N 2 O production by co-denitrification prevailed against N 2 O from denitrification and abiotic hydroxylamine decomposition. In addition, a formation of hybrid N 2 was also calculated by the model. However, the experimental results lead to the conclusion that it was most likely caused by a reduction of hybrid N 2 O due to conventional denitrification.

Description: The subcellular distribution and chemical forms of different heavy metals in rice are correlated with their bio-toxicity. An experiment was conducted to investigate the subcellular distribution and chemical forms of chromium (Cr) in two rice genotypes ( Oryza sativa L. cv. Xiushui 113 and cv. Dan K5) differing in Cr accumulation, to understand the mechanisms of Cr toxicity and resistance in rice plants. The results show that Cr in the roots of rice plants exposed to Cr stress was mainly localized in cell walls, whereas Cr in leaves and stems was mainly present in both cell walls and vacuoles, suggesting that both compartments act as important protective barriers against Cr toxicity in rice plants. Although Cr ions in all plant tissues exist predominantly in the forms extracted by 80% ethanol and distilled water, the amount of Cr in the chemical forms extracted by 2% HAc, 0.6 M HCl, and in residues was significantly increased under the highest Cr level (100 μM Cr) compared to the plants grown under lower Cr levels. These results indicate that excess Cr accumulated in rice plants under Cr stress is bound to undissolved or low-bioavailable compounds, such as undissolved phosphate and oxalate, being beneficial for rice plants to alleviate Cr toxicity. In addition, under the highest Cr level (100 μM), Dan K5 had a higher percentage of Cr in the chemical forms extracted by 2% HAc, 0.6 M HCl, and in residues compared to Xiushui 113 in both stems and leaves, indicating that more Cr ions in shoots of Dan K5 were bound to undissolved or low-bioavailable compounds, in comparison with those of Xiushui 113. It is evident that the low bioavailability of Cr in the shoots of Dan K5 is related to a high Cr accumulation.

Description: Crops grown in seleniferous soil may accumulate selenium (Se) to levels considered highly toxic for animal and human consumption. Furthermore, higher Se content in plant tissues leads to considerable deterioration in product quality. Application of organic amendments plays an important role in improving soil physical, chemical, and biological conditions and influencing nutrient availability. A field trial was conducted to evaluate the effect of organic amendments, namely poultry manure (PM), sugar cane press mud (SCPM), and farmyard manure (FYM), on Se uptake and grain quality of wheat and oilseed rape grown on a seleniferous soil in Punjab, India. Selenium accumulation by wheat and oilseed rape grains decreased significantly (75%–95%) with the application of PM and SCPM, while FYM application resulted in a significant decrease (23%) only in case of wheat grains. The amount of Se associated with seed proteins varied in proportion to its uptake under different treatments. Quality of wheat grains improved considerably with respect to total soluble sugars, reducing sugars, starch, lipids, and sulfur concentrations only after application of SCPM and PM. Treating a Se-contaminated soil with organic amendments significantly increased the oil concentration and changed the proportion of various fatty acids in rape grains. It is concluded that applying organic amendments to Se-contaminated soils can alleviate the deleterious effects of Se and restore the nutritional quality of grains.

Description: In the near future, composted bio-solids are expected to play a major role in agriculture. In order to evaluate their contribution to plant growth and nutrition, a mixed sorghum–poultry manure compost was prepared using 15 N-labeled materials. Four treatments were compared in a pot trial: fertilized with compost vs. unfertilized, both of them combined with (cultivated) and without (bare) plants of fibre sorghum ( Sorghum bicolor [L.] Moench.). Soil mineral nitrogen (N-min), plant growth, and N uptake were monitored over a whole growing season (167 d after fertilizer treatment; DAT). Apparent soil mineralization (ASM) and apparent recovery fraction of nitrogen by the plant (ARF) were assessed, as well as the 15 N recovery fraction by the plant ( 15 NRF). Compost enhanced sorghum biomass at mid growth (+ 200% of dry weight compared to the unfertilized). However, the difference between the control and the fertilized plants progressively decreased towards the end of the season (+ 70%). Fertilized and unfertilized plants followed different growth patterns over time, although of the same sigmoid type. Conversely, N concentration in plant tissues followed a common dilution curve, indicating that fertilized sorghum efficiently used the supplied N, avoiding luxury consumption. Apparent soil mineralization approximately reached 45% of compost total N in pots without plants. Apparent recovery fraction attained 100% at about two third of the growing season (DAT 111), then declined to about 50% because of root and leaf decline. Compared to it, 15 NRF only reached ≈ 20% at mid growth (DAT 83), then declined to 12%. Despite the large difference in absolute values, ARF and 15 NRF exhibited a significant correlation, indicating a common trend in time. In contrast to 15 NRF, the amount of nutrient derived from fertilizer (Ndff) taken up by the plant decreased over the growth season, proving that compost contributed more to plant nutrition in the early (Ndff ≈ 50%) than in the late growing season (Ndff ≈ 25%). The large difference between ARF and 15 NRF suggests that sorghum exerted a strong nutrient demand on the soil and on the fertilizer. Both 15 NRF and ARF are considered valuable traits: the former better describes fertilizer behavior and actual supply of N, while the latter outlines the overall effect of fertilizer application on crop nutrition.

Description: This study was designed to examine whether external selenium (Se) may improve the tolerance of Trifolium repens L. to polyethylene glycol (PEG)–induced water deficit, and to determine the physiological mechanisms of the possibly enhanced tolerance. Trifolium repens seedlings were subjected to PEG-induced water deficit alone or combined with 5 μM Na 2 SeO 4 for 24, 48, and 72 h. During the experimental period, the fresh weight (FW) of T. repens seedlings and the relative water content (RWC) of the leaves decreased gradually, and the chlorophyll concentration increased after 24 and 48 h, but decreased after 72 h. The PEG+Se-treated plants had higher FW, RWC, and chlorophyll concentration than the PEG-treated plants. Smaller amounts of thiobarbituric acid-reactive substances (TBARS) and H 2 O 2 accumulated in PEG+Se-treated plants than in plants treated only with PEG. The activity of superoxide dismutase (SOD) increased gradually during the water-deficit period, and Se application promoted SOD activity further. Catalase (CAT) activity remained unchanged after 24 and 48 h and insignificantly increased after 72 h of water deficit, whereas ascorbate peroxidase (APOX) activity increased linearly and glutathione reductase (GR) activity increased slightly over the course of treatment. Whereas the Se application exhibited no effect on the CAT activity, seedlings treated with PEG+Se had higher APOX activity during the whole experimental period and a higher GR activity after 48 and 72 h than PEG-treated plants. These results suggest that exogenous Se treatment enhanced T. repens tolerance to PEG-induced water deficit, and this enhancement was related to alleviation of lipid peroxidation and activation of antioxidant enzymes such as SOD, APOX, and GR.

Description: Currently, potassium (K)- and phosphate (P)-fertilizer recommendation in Germany is based on standardized soil-testing procedures, the results of which are interpreted in terms of nutrient availability. Although site-specific soil and plant properties ( e.g. , clay and carbon content, pH, crop species) influence the relation between soil nutrient content and fertilizer effectiveness, most of these factors are not accounted for quantitatively when assessing fertilizer demand. Recent re-evaluations of field observations suggest that even for soil nutrient contents well within the range considered to indicate P or K deficiency, fertilizer applications often resulted in no yield increase. In this study, results from P- and K-fertilization trials (in total about 9000 experimental harvests) conducted during the past decades in Germany and Austria were re-analyzed using a nonparametric data-mining procedure which consists of a successive segmentation of the data pool in order to elaborate a modified recommendation scheme. In addition to soil nutrient content, fertilizer-application rates, nutrient-use efficiency, and site properties such as pH, clay content, and soil organic matter, have a distinct influence on yield increase compared to an unfertilized control. For K, nutrient-use efficiency had the largest influence, followed by soil-test K content, whereas for P, the influence of soil-test P content was largest, followed by pH and clay content. The results may be used in a novel approach to predict the probability of yield increase for a specified combination of crop species, fertilizer-application rate, and site-specific data.

Description: Ecosystems are characterized as complex systems with abiotic and biotic processes interacting between the various components that have evolved over long-term periods. Most ecosystem studies so far have been carried out in mature systems. Only limited knowledge exists on the very initial phase of ecosystem development. Concepts on the development of ecosystems are often based on assumptions and extrapolations with respect to structure–process interactions in the initial stage. To characterize the effect of this initial phase on structure and functioning of ecosystems in later stages, it is necessary to disentangle the close interaction of spatial and temporal patterns of ecosystem structural assemblages with processes of ecosystem development. The study of initial, less complex systems could help to better identify and characterize coupled patterns and processes. This paper gives an overview of concepts for the initial development of different ecosystem compartments and identifies open questions and research gaps. The artificial catchment site “Chicken Creek” is introduced as a new research approach to investigate these patterns and processes of initial ecosystem development under defined boundary conditions. This approach allows to integrate the relevant processes with related pattern and structure development over temporal and spatial scales and to derive thresholds and stages in state and functioning of ecosystems at the catchment level.

Description: Our understanding of nutrient and carbon (C) fluxes in irrigated organic cropping systems of subtropical regions is limited. Therefore, leaching of mineral nitrogen (N) and phosphorus (P), gaseous emissions of NH 3 , N 2 O, CO 2 , and CH 4 , and total matter balances were measured over 24 months comprising a total cropping period of 260 d in an organic-cropping-systems experiment near Sohar (Oman). The experiment on an irrigated sandy soil with four replications comprised two manure types (ORG1 and ORG2) characterized by respective C : N ratios of 19 and 25 and neutral detergent fiber (NDF)-to-soluble carbohydrates (SC) ratios of 17 and 108. A mineral-fertilizer (MIN) treatment with equivalent levels of mineral N, P, and potassium (K) served as a control. The three treatments were factorially combined with a cropping sequence comprising radish ( Raphanus sativus L.) followed by cauliflower ( Brassica oleracea L. var. botrytis ) or carrot ( Daucus carota subsp. sativus ). Over the 24-months experimental period gaseous N emissions averaged 45 kg ha –1 (59% NH 3 -N, 41%N 2 O-N) for MIN, 55 kg N ha –1 (69% NH 3 -N, 31%N 2 O-N) for ORG1, and 49 kg N ha –1 (59% NH 3 -N, 41% N 2 O-N) for ORG2. Carbon losses were 6.2 t ha –1 (98% CO 2 -C, 2% CH 4 -C) for MIN, 9.7 t C ha –1 (99% CO 2 -C, 1% CH 4 -C) for ORG1, and 10.6 t ha –1 (98% CO 2 -C, 2% CH 4 -C) for ORG2. Exchange resin–based cumulative leaching of mineral N amounted to 30 kg ha –1 for MIN, 10 kg ha –1 for ORG1, and 56 kg ha –1 for ORG2. Apparent surpluses of 361 kg N ha –1 and 196 kg P ha –1 for radish-carrot and 299 kg N ha –1 and 184 kg P ha –1 for radish-cauliflower were accompanied by K deficits of –59 kg ha –1 and –73 kg ha –1 , respectively, for both cropping systems. Net C balances for MIN, ORG1, and ORG2 plots were –7.3, –3.1, and 1.5 t C ha –1 for radish-carrot and –5.0, 1.3, and 4.6 t C ha –1 for radish-cauliflower. The results underline the difficulty to maintain soil C levels in intensively cultivated, irrigated subtropical soils.

Description: Despite a general consent about the beneficial contribution of arbuscular mycorrhizal fungi (AMF) on natural ecosystems, there is an intense debate about their role in agricultural systems. In this work, soybean ( Glycine max L.) and sunflower ( Helianthus annuus L.) field plots with different P availabilities were sampled across the Pampean Region of Argentina (〉 150 samples from Mollisols) to characterize the relationship between available soil P and indigenous mycorrhizal colonization. A subsequent pot experiment with soybean and sunflower was carried out to evaluate the effect of P supply (0, 12, and 52 mg P kg –1 ) and AMF inoculation on AMF colonization and crop responsiveness to P in a Mollisol. Both crops showed high AMF colonization in the field (average: 55% for soybean and 44% for sunflower). While mycorrhizal colonization in soybean was significantly and negatively related to available soil P, no such trends were apparent in sunflower. Also, total biomass was 3.5 and 2.0 times higher in mycorrhizal than in nonmycorrhizal pot-grown soybean under low- and medium-P conditions, respectively. Sunflower, on the other hand, did not benefit from AMF symbiosis under medium and high P supply. While mycorrhization stimulated P-uptake efficiency in soybean, the generally high P efficiency in sunflower was not associated with AMF symbiosis.

Description: Microbial-community structure is closely associated with plant-community composition. The objective of this study was to evaluate the effects of depth and revegetation time on the microbial-community structure of restored grassland soils of the Loess Plateau of China. Microbial-community structure at 0–10 cm (depth 1) and 10–20 cm (depth 2) of eight sites of a grassland chronosequence with revegetation time ranging from 1 to 78 y was determined using phospholipid fatty acid (PLFA) analysis. Except for the youngest site microbial-community structure at the two depths varied distinctly with actinomycetes and vesicular arbuscular mycorrhiza as the most important discriminators. Total PLFA content decreased with depth and increased with revegetation time. Protozoa were the only functional group whose proportion did not change with depth. Their relative abundance tended to decrease with increasing revegetation time. The microbial community at all sites was bacteria-dominated with Gram-negative bacteria representing the largest proportion. Principal-component and cluster analysis revealed that microbial-community structure in the surface soil (depth 1) of the older sites (23–78 y of revegetation) was rather similar which may be due to only small effects of the plant species present on the soil environment. Differences in microbial-community composition at 0–20 cm depth of the eight sites were partly related to variations in the physico-chemical characteristics. Relations to organic C, alkali-extractable N, pH, and available P were found. Revegetation of former agricultural sites on the Loess Plateau improves the soil status and leads to shifts in microbial-community structure more pronounced with depth than time.

Description: Differences in the mechanisms of storage and decomposition of organic matter (OM) between minimum tillage (MT) and conventional tillage (CT) are generally attributed to differences in the physical impact through tillage, but less is known about the effects of residue location. We conducted an incubation experiment at a water content of 60% of the maximum water-holding capacity and 15°C with soils from CT (0–25 cm tillage depth) and MT fields (0–5 cm tillage depth) with 15 N-labeled maize straw incorporated to different depths (CT simulations: 0–15 cm; MT simulations: 0–5 cm) for 28 d in order to determine the effects of the tillage simulation on (1) mineralization of recently added residues, (2) the dynamics of macroaggregate formation and physical protection of OM, and (3) the partitioning of maize-derived C and N within soil OM fractions. The MT simulations showed lower relative C losses, and the amount of maize-C mineralized after 28 d of incubation was slightly but significantly lower in the MT simulations with maize added (MT maize ) than in the respective CT (CT maize ) simulations. The formation of new water-stable macroaggregates occurred during the phase of the highest microbial activity, with a maximum peak 8 d after the start of incubation. The newly formed macroaggregates were an important location for the short-term stabilization of C and N with a higher importance for MT maize than for CT maize simulations. In conclusion, our results suggest that a higher amount of OM in MT surface soils compared with CT surface soils may not only result from decreased macroaggregate destruction under reduced tillage but also from a higher efficiency of C retention due to a more concentrated residue input.

Description: Phosphorus (P) nutrition has been suggested to play a role in the alleviation of manganese (Mn) toxicity in some higher plant species. However, there are few reports on the role of P in regulating Mn accumulation by forage species. We studied the effect of P nutrition on Mn toxicity in Lolium perenne L. and Trifolium repens L. An increase in Mn concentration in root and shoot tissues was associated with an increase in both P supply and P tissue concentrations. Nevertheless, in both forage species, especially white clover, plant-growth inhibition caused by Mn excess was decreased with increasing P additions. Moreover, the carboxylate exudation that had increased in response to high Mn was gradually reduced by increasing P supply. We suggest that P supply may have a beneficial effect in reducing the severity of Mn toxicity in forage species.

Description: To investigate C and N rhizodeposition, plants can be 13 C- 15 N double-labeled with glucose and urea using a stem-feeding method (wick method). However, it is unclear how the 13 C applied as glucose is released into the soil as rhizorespiration in comparison with the 13 C applied as CO 2 using a natural uptake pathway. In the present study, we therefore compared the short-term fate of 14 C and 15 N in white lupine and pea plants applied either by the wick method or the natural pathways of C and N assimilation. Plants were pulse-labeled in 14 CO 2 -enriched atmosphere and 15 N urea was applied to the roots (atmosphere–soil) following the natural assimilation pathways, or plants were simultaneously labeled with 14 C and 15 N by applying a 14 C glucose– 15 N urea solution into the stem using the wick method. Plant development, soil microbial biomass, total rhizorespiration, and distribution of N in plants were not affected by the labeling method used but by plant species. However, the 15 N : N ratio in plant parts was significantly ( p 〈 0.05) affected by the labeling method, indicating more homogeneous 15 N enrichment of plants labeled via root uptake. After 14 CO 2 atmosphere labeling of plants, the cumulated 14 CO 2 release from roots and soil showed the common saturation dynamics. In contrast, after 14 C-glucose labeling by the wick method, the cumulated 14 CO 2 release increased linearly. These results show that 14 C applied as glucose using the wick method is not rapidly transferred to the roots as compared to a short-term 14 CO 2 pulse. This is partly due to a slower 14 C uptake and partly due to slow distribution within the plant. Consequently, 14 C-glucose application by the wick method is no pulse-labeling approach. However, the advantages of the wick method for 13 C- 15 N double labeling for estimating rhizodeposition especially under field conditions requires further methodological research.

Description: Partial rootzone drying (PRD) is a water-saving irrigation technology that may affect apple ( Malus domestica Borkh cv. Golden Delicious/Malling7)-tree nutrition if applied for an extended period. The objective of this study was to test the hypothesis that long-term application of PRD causes seasonal changes in macro- and micronutrients of apple leaves. The irrigation treatments were: (1) commercial irrigation as control (CI) and (2) PRD. After 3 years of evaluation, PRD irrigation had saved about 3240 m 3 of water per hectare. Leaf xylem water potential was slightly lower in the PRD treatment than in CI. The seasonal concentration of macro- and micronutrients was comparable between treatments, although significant differences were found at times. The macronutrient concentrations were within the normal range in PRD apple leaves. All micronutrient concentrations were slightly above the normal range except for Zn, which was slightly below the normal range. No physiological disorders associated with plant nutrition were observed on leaves or fruits. Therefore, data suggest that PRD did not alter apple-tree nutrition during the 3-year trial. Thus, PRD may be feasible for apple production in Central Mexico. However, further studies need to be conducted in those regions where groundwater is the main water source for irrigation and rain is negligible, particularly during the growing season.

Description: Bare-root transplants of strawberry ( Fragaria × ananassa Duch. cv. Selva) were transferred to nutrient solutions with or without iron. After 35 d of growth, plants in the solution without iron became chlorotic and had morphological changes in roots typical of iron-deficiency chlorosis (IDC). Acidification of the nutrient solution was also observed. We tested a grass-clipping extract to correct IDC in strawberry plants by foliar application to some chlorotic plants. We also assessed the effects of this product on plant growth, Fe allocation, as well as morphological and physiological parameters related with IDC. After the second spray, leaf chlorophyll increased in the youngest expanded leaves. The total content of iron in plants increased from 1.93 mg to 2.37 mg per plant after three sprays, accounting for 80% of the total iron supplied by the extract. Newly formed roots from sprayed plants had a normal morphology (no subapical swollen zone) but a higher ferric chelate–reductase (FC-R; EC 1.16.1.17) activity per root apex compared with roots from plants grown with iron or untreated chlorotic plants. Acidification of the nutrient solution continued in sprayed recovered plants. The results suggest an uncoupling of the regulation of morphological and physiological mechanisms related to IDC: FC-R activity seems to be controlled by roots on their own or together with shoots, while morphological changes in roots are apparently regulated only by the level of iron in shoots.

Description: Closed-chamber systems are commonly used to determine gaseous C and N emissions from agricultural soils. We investigated the effects of eight cuvette surfaces on two standard gas concentrations of NH 3 , N 2 O, CO 2 , and CH 4 under laboratory conditions. Cuvette surface materials differentially affected gas adhesion or recovery as a function of the type and the concentration of the gases. Given the strong effects on results of gas measurements in closed-chamber systems, both the type and the concentration of the measured gases need to be considered in selecting cuvette surface materials.

Description: Kochia sieversiana (Pall.) C. A. Mey is a forage plant in the family Chenopodiaceae, which can grow in extremely alkalinized grasslands at pH levels of 10 or higher. Kochia sieversiana often contains a large amount of oxalic acid. In the present study, seedlings of K. sieversiana were exposed to the following conditions: nonstress, salt stress (molar ratio of NaCl : Na 2 SO 4 = 1:1, salinity: 200 mM), and alkali stress (molar ratio of NaHCO 3 : Na 2 CO 3 = 1:1, salinity: 200 mM). By determining and analyzing various physiological factors such as the concentrations and distribution of different organic acids (including oxalic acid) in various parts of K. sieversiana , the concentrations of inorganic ions (K + , Na + , Cl – , SO , etc. ), the organic solutes (proline, betaine, and soluble sugar) in shoots, and the accumulation and distribution of oxalic acid in K. sieversiana, the physiological contribution of oxalic acid to K. sieversiana adaptability to saline and alkaline conditions was investigated. Results show that oxalic acid mainly accumulated in shoots, and that its concentration was highest in mature functional leaves where photosynthesis productivity was based and lowest in old stems and roots, regardless of plant treatment (nonstress, salt, or alkali conditions). Under nonstress, salt, and alkali conditions, the concentrations of oxalic acid in mature leaves were 8%, 10%, and 12% of their dry weights, respectively, and were 1%, 0.7%, and 0.6% of dry weights, respectively, in roots. There were varying effects of salt and alkali conditions on oxalic acid concentrations in different parts of K. sieversiana. Oxalic acid concentration increased in leaves, did not change significantly in young stems, and decreased in old stems and roots. The present analysis shows that oxalic acid exists as an organic anion in K. sieversiana. Consequently, oxalic acid not only plays a crucial role in osmoregulation and pH adjustment, but it also is the dominant contributor of negative charge, playing a key role in maintaining ionic balance in vivo. Oxalic acid in K. sieversiana shoots is a key substance on which the adaptation to saline and alkaline conditions is based.

Description: We investigated the effects of land uses on P distribution and availability in selected calcareous soils under different management practices. KCl-P (labile P), NaOH-P (Fe-Al-bound P), HCl-P (Ca-bound P), and residual P (Res-P) fractions at 0–30 cm depth were determined for soils planted to garlic, orchard, pasture, potato, leafy vegetables, and wheat. Trends in P distribution between chemical fractions were similar between land uses. Ca-bound P was the most abundant P fraction in the soils, constituting between 61% and 78% of the total P, whereas P associated with labile was less abundant (〈 2%). Soils under leafy vegetables and wheat along with pasture presented the highest and lowest values in all fractions of P, respectively. Labile P generally was highest for leafy vegetables and potato. Labile P and Fe-Al-bound P comprised 〈 1.4% and 8% of total P, respectively. Residual P ranged from ≈ 14% (potato and garlic) to 31% (pasture). Long-term fertilization increased P allocation to inorganic fractions, as Ca-bound P contained 78% of total P for potato and garlic and 74% for leafy vegetables but 61% for pasture. A strong positive correlation between labile P and Fe-Al-bound P ( r = 0.534, p 〈 0.01), labile P and Ca-bound P ( r = 0.574, p 〈 0.01), Ca-bound P and Fe-Al-bound P ( r = 0.504, p 〈 0.01), Olsen-P and CaCl 2 -P ( r = 0.821, p 〈 0.01) was found. Principal-component analysis showed that the first four components accounted for most of the variation, 32.5%, 16.9%, 12.9%, and 7.9% of total variation, respectively.

Description: Some formulations of phosphite (Phi) have been recommended as a source of P nutrition for several crops including citrus even though there are known negative effects of Phi on plant growth. Changes in plant growth and metabolism after Phi application should be reflected in altered nutrient-use efficiency and leaf photosynthesis. We carried out a greenhouse study using seedlings of two contrasting citrus ( Citrus spp. ) rootstocks, Carrizo citrange (CC), and Smooth Flat Seville (SFS), growing in either aerated hydroponic culture or sterilized native sandy soil. Plants were subjected to four P treatments: No P (control, P 0 ); 0.5 mM P i (PO 4 -P); 0.25 mM P i + 0.25 mM Phi (P i + Phi), or 0.5 mM Phi (Phi). Photosynthetic characteristics, concentrations of total P (P t ) and soluble PO 4 -P or PO 3 -P in leaves and roots, and plant growth were evaluated after 80–83 d P treatments. Overall, the P i plants had the highest P t (total P) and total plant dry weight while the P 0 plants had the lowest P t but highest total root length and root-to-shoot ratio. Leaf chlorophyll (SPAD readings) and net assimilation of CO 2 ( A CO2 ) of the P 0 and Phi plants were similarly lower than those of P i and P i + Phi plants. Growth responses of the P i + Phi treatment were intermediate between the P i and Phi treatments. Although Phi increased P t and soluble-PO 4 -P concentration in leaves and roots above the P 0 treatment, this did not translate into increased plant growth. In fact, the Phi treatment had some phytotoxic symptoms, impaired P- and N-utilization efficiency for biomass production as well as lower nutrient-use efficiency in the photosynthetic process. Thus, these two rootstocks could not use Phi as a nutritional source of P.

Description: Column experiments were conducted over 45 d to determine the degree of P mobility. The sandy loam soil was spiked with 200 mg P kg –1 and 5% organic residues. The treatments included: control without any water-soluble P and plant residues, potato, wheat, water-soluble P fertilizer, wheat + water-soluble P, and potato + water-soluble P. Each column was leached with distilled water, and leachates were collected and analyzed for P, K + , Ca 2+ , Mg 2+ , along with pH and EC. Sequential extraction was performed on soil samples at the end of leaching column experiments. The relatively high initial concentration of P in the leachates decreased to more stable values after 15 d which can be attributed to the colloid-bound P. The P concentrations in the leachates fluctuated between 8 and 220 mg L –1 in the water-soluble–P fertilizer treatment, between 0.80 and 230 mg L –1 in the potato + water-soluble-P treatment, and between 0.90 and 214 mg L –1 in the wheat + water-soluble P treatment. Leaching loss of P mainly occurred in the 15 d of leaching, accounting for 94%, 88%, and 65% of total P leached in wheat + water-soluble-P, potato + water-soluble-P, and water-soluble-P treatments, respectively. Maximum amount of P leached was found from an exponential kind model and was in the range 0.45 mg kg –1 to 125.4 mg kg –1 in control and potato + water-soluble-P treatments, respectively. Sequential extraction results showed that in control and amended soils the major proportion of P was associated with Ca. The leachate samples in all treatments were saturated with respect to hydroxyapatite, β-tricalcium phosphate, and octacalcium phosphate up to 20 d of leaching, whereas they were undersaturated with respect to Mg-P minerals through the entire leaching experiment.

Description: Intercropping is an important and widespread land-management system in the tropics. At two agricultural sites in Central Kenya differing in elevation and soil type Haplic Nitisols (eutric) and Vitric Gleysols (eutric, epiclayic, endoclayic), we investigated the vertical root distributions using the trench wall profile method in single-crop systems of maize ( Zea mays L.) and in intercropping systems of maize and legumes (common bean, Phaseolus vulgaris L.; pigeon pea, Cajanus cajan [L.] Millsp.) to test for possible differences in the use of water and nutrient resources. The physico-chemical soil properties of the sites were similar and imposed no restrictions to the vertical growth of the roots into soil depths of 1.4 m. The vertical distributions of the fine roots (∅ 0.5–2 mm) and very fine roots (∅ 〈 0.5 mm) were quantified by calculating the parameter β which was computed from the cumulative fraction ( Y ) of the root densities along the depth ( d ) of the soil profiles ( Y = 1 – β d ). We found no consistent differences between the single-crop and the intercropping systems in the rooting depth down to 1.4 m. However, higher β values for fine roots of the intercropping systems were indicative of a more homogeneous vertical root distribution than in the single-crop fields. In the intercropping fields, 50% of the total number of fine roots were distributed over the uppermost 36 cm of the soil, whereas in the single-crop fields, 50% of the fine roots were concentrated in the uppermost 15–21 cm. Medium-sized roots (∅ 〉 2–5 mm) were detected in the intercropping fields only. The more homogeneous root distribution in the intercropping fields likely indicates a more efficient use of the limited resources nutrients and water.

Description: The effects of wheat, potato, sunflower, and rape residues and calcite were evaluated in soil that received sodic water. These materials were added to a sandy-loam soil at a rate of 5%, after which the treated soils were incubated for 1 month at field-capacity moisture and a temperature of 25°C–30°C. Column leaching experiments using treated soils were then conducted under saturated conditions using water with three sodium-adsorption ratios (SAR) (0, 10, 40) with a constant ionic strength (50 mmol L –1 ). The results indicated that the application of plant residues to soils caused an increase in cation-exchange capacity and exchangeable cations. Leaching experiments indicated that the addition of plant amendments led to increased Na + leaching and decrease in exchangeable-sodium percentage (ESP). The ESP of the control soil, after leaching with solutions with an SAR of 10 and 40, increased significantly, but the level of sodification in soils treated with plant residue was lower. Such decreases of soil ESP were greatly affected by the type of plant residues, with the order of: potato-treated soil 〉 sunflower-treated soil 〉 rape-treated soil 〉 wheat-treated soil 〉 calcite-treated soil 〉 control soil.

Description: In acidified forest soils, the coarse-soil fraction is a potential nutrient source. Plant nutrient uptake from the coarse-soil fraction is aided by ectomycorrhiza. Similarly, (recalcitrant) organic matter (OM) is an important nutrient source largely made plant-available through (symbiotic) microorganisms, especially in the topsoil. We hypothesized that in a podzol profile, fungal hyphae would concentrate in nutrient hotspots, either OM or the coarse-soil fraction. Absolute hyphal length, base saturation, and organic-C content of a Podzol profile were determined in the fine-earth and coarse-soil fractions. In the fine-earth fraction, hyphae were attracted by the organic-C content and relative high base saturation. In the coarse-soil fraction of the BhBs horizon, the absolute hyphal length exceeded the hyphal length in the fine earth by factor 3, yet C content and base saturation were lowest. We could not determine to what fungi the hyphae belonged. Most likely ectomycorrhiza, ericoid mycorrhiza and saprotrophic fungi dominate the upper soil layers of this profile and all utilize OM for nutrition. In the deeper mineral horizons and especially in the coarse-soil fraction, ectomycorrhiza are better adapted than other fungi to harvest nutrients from inorganic sources. Additionally, favorable physical properties may explain the high amount of fungal hyphae in the coarse-soil fraction of the BhBs horizon. Both the coarse-soil fraction and deeper mineral soil horizons may play a more active role in microbial nutrient cycling than previously assumed.

Description: A flue dust originaly enriched in metal sulfides evolved as a by-product of Cu smelting. The dust was deposited as slurry in unsealed heaps. It is characterized by very high contents of toxic metals such as Pb and Zn. The slurry is a source of soil, sediment, and water contamination. We studied a Technosol profile developed from deposited flue-dust slurry by means of chemical and mineralogical characterization (SEM-EDX, XRD, FTIR, DTA-MS, XRF, Pb isotopes), by open-flow and closed-flow column experiments on contaminant release under water-saturated conditions, and by geochemical modeling to evaluate release processes and to quantify aqueous contaminant concentrations. Besides ash particles and quartz, the flue-dust slurry contains Fe oxides, silicates, sulfates, and sulfides (in varying states of weathering). In both column approaches, metal concentrations exceed inspection values. The concentration patterns in both experimental column approaches indicate near-equilibrium mineral dissolution. Geochemical modeling reveals partial dissolution of sulfates and precipitation of secondary carbonates. Their precipitation prevents complete sulfate dissolution, which would have led to even higher aqueous metal concentrations and contaminant export. The combination of detailed material characterization, column experiments, and modeling allows for quantitative and qualitative estimation of contaminant release into the soil solution.

Description: In this study, we evaluated how increased cation supply can alleviate the toxic effects of NaCl on plants and how it affects essential oils (EOs) and phenolic diterpene composition in leaves of rosemary ( Rosmarinus officinalis L.) plants grown in pots. Two concentrations of the chloride salts KCl, CaCl 2 , MgCl 2 , and FeCl 3 were used together with 100 mM NaCl to study the effects of these nutrients on plant mineral nutrition and leaf monoterpene, phenolic diterpene, and EO composition. The addition of 100 mM NaCl, which decreased K + , Ca 2+ , and Mg 2+ concentrations with increasing Na + in leaves, significantly altered secondary metabolite accumulation. Addition of MgCl 2 and FeCl 3 altered leaf EO composition in 100 mM NaCl–treated rosemary plants while KCl and CaCl 2 did not. Furthermore, addition of CaCl 2 promoted the accumulation of the major phenolic diterpene, carnosic acid, in the leaves. The carnosol concentration was reduced by the addition of KCl to salt-stressed plants. It is concluded that different salt applications in combination with NaCl treatment may have a pronounced effect on phenolic diterpene and EO composition in rosemary leaves thus indicating that ionic interactions may be carefully considered in the cultivation of these species to achieve the desired concentrations of these secondary metabolites.

Description: A pot experiment was conducted to study the contribution of reactive phosphate rocks (RPRs) on the accumulation of Cd and Zn in 10 acid upland soils in Indonesia and shoots of Zea mays plants grown on these soils. Two types of RPR were used at a rate of 0.5 g (kg soil) –1 : RPRL containing 4 mg Cd kg –1 and 224 mg Zn kg –1 , and RPRH containing 69 mg Cd kg –1 and 745 mg Zn kg –1 . Zea mays was harvested at 6 weeks after planting. The application of RPRH significantly increased the concentrations of Cd in the shoots. The application of this RPR also increased the amount of Cd which could be extracted by 0.5 M NH 4 -acetate + 0.02 M EDTA pH 4.65 from the soils. More than 90% of the added Cd remained in the soil. As Zn is an essential element and the studied acid upland soils are Zn-deficient, increased plant growth upon RPR application might be partly attributed to Zn present in the phosphate rock. However, more experiments are needed to confirm this hypothesis. The Cd and Zn concentrations and CEC of the soils were important soil factors influencing the concentrations of Cd and Zn in the shoots of maize plants grown on these soils.

Description: Silicon (Si) is a beneficial element for tropical grasses such as rice ( Oryza sativa ) and responses to applications of Si are common on highly weathered soils. However, the importance of pH (and hence Si speciation), weathering and fertilisation on Si uptake is still poorly understood. The responses of rice to Si fertilisation were studied in two variably weathered basalt soils (Red Ferrosol, Grey Vertosol) adjusted at different pH values (5.5–9.5) with three levels of acidulated wollastonite. Soil Si was extracted using deionised water (H 2 O), 0.01 M CaCl 2 , or 0.5 M NH 4 OAc. Significant increases in Si uptake and rice biomass were observed in the Red Ferrosol following fertilisation ( p 〈 0.01). Greater biomass production was observed at lower pH, due to decreased Si sorption and higher solution Si concentrations. Silicon uptake by rice was greater at low pH, despite similar extractable Si concentrations; suggesting a relationship between Si speciation and uptake. In contrast, Si uptake and rice shoot dry matter in the less weathered Grey Vertosol were unaffected by Si fertilisation ( p 〉 0.05) except at the highest rate and lowest pH (5.5). Solution Si concentrations were controlled by precipitation/polymerisation reactions in equilibrium with specific soil pH values rather than adsorption processes. Silicon speciation effects (monosilicic acid vs. silicate ions) were unable to be measured due to an induced phosphorus deficiency in both soils at pH values 〉 8.5. In conclusion, weathered soils are more responsive to Si fertilisation and Si uptake is increased at low pH.

Description: Unusually low net N mineralization in soils relatively rich in total organic C and N was repeatedly reported for sandy arable soils in NW Europe. In order to adequately account for it in simulation models, it is necessary to know the involved substances and processes. Therefore, 9 arable top soils (〈 6% clay) with a wide range of total organic C (1.1%–5.2%) and C : N ratios (12–35) were studied. The soils varied strongly in the mineralizability of soil organic N which was determined via long-term laboratory incubations (〉 200 d). It was hypothesized that mineralization was controlled by antioxidants, and the Trolox equivalent antioxidant capacity (TEAC) of the soils was measured. In addition, pyrolysis–field ionization mass spectrometry (Py-FIMS) was applied to investigate the influence of the molecular-chemical composition of soil organic matter. In these soils, the compound class of sterols from Py-FIMS analysis was most closely, negatively correlated with the mineralizability of soil organic N ( r 〈?h.3〉 2 = 0.75, p = 0.003). This was probably not an antioxidative effect, because the TEAC values did not correlate sufficiently with the mineralizability and the sterol intensities. However, the negative relation with sterols could be causal, since the correlation was about as close with other components of the compound class of sterols and even closer with the main plant sterol beta-sitosterol ( r 〈?h.3〉 2 = 0.84, p = 0.001). In addition, the variability among samples was strongly governed by the proportions of sterols, and sterols also had a high discriminating power in discriminant analysis. Furthermore, the proportions of sterols were extraordinary in those arable podzol soils that developed under previous heath- or woodland (up to 10.2% of total ion intensity from Py-FIMS). In conclusion, the inhibitory effect of these compounds needs to be investigated in more detail in order to optimize parameterization of N as well as C simulation models especially for podzolized, sandy arable soils with former heath- or woodland vegetation.

Description: This paper presents the influence of selected methodological aspects on the results of particle-size distribution (PSD) as measured by the laser diffraction method (LDM). The investigations were carried out using the Mastersizer 2000 with Hydro MU attachment (Malvern Ltd., UK). It was found that for the investigated soils: (1) optimal speed of pump and stirrer was 2500 rpm, (2) optimal measurement time was ≈ 1 min, (3) there are two, practically equivalent methods for soil-sample dispersion: chemical (with the use of a solution of sodium hexametaphosphate) or physical (by means of ultrasound application for 4 min at a maximum power of 35W), (4) one must not use the chemical and physical dispersing methods simultaneously, because this can lead to aggregation (not dispersion) of soil particles, (5) the Fraunhofer theory (physical models) can be used to convert scattered-light data to PSD. In the case of the Mie theory, the best results were obtained for a refractive index (RI) in the range of 1.5–1.6 and an absorption index (AI) of 1.0. It was also found that most of the discussed parameters depend on design of the measuring device and on the type and volume of the investigated suspensions. It is necessary, therefore, to explain how the data was obtained every time and to specify the details in the methodological part of the paper.

Description: A study was conducted to evaluate the distribution and origin of trace elements (Ti, Fe, Nb, Pb, Rb, Sr, Y, and Zr) in five representative long-term wastewater-irrigated urban vegetable gardens of Kano, Nigeria. Surface-soil concentrations (0–15 cm) of Ti (4600–14 300 mg kg –1 ), Fe (4000–31 800 mg kg –1 ), Pb (96–355 mg kg –1 ), and Y (33–98 mg kg –1 ) were high compared to mean concentrations in comparable soils elsewhere. However, soil-pollution assessment yielded no evidence of anthropogenic input of the trace elements studied. Indices such as the enrichment factor, the contamination factor, and the geoaccumulation index ( I geo ) revealed little to no contamination with trace elements. The I geo calculated for these metals varied across locations between 0.00 and 0.12 with Nb having the highest I geo value. Similarly, the contamination factor was low for all metals with the exception of Fe reaching a contamination factor of 4.2 at one location. Geochemical-balance evaluations showed depletion of all trace elements except for Fe which was 176% higher than in a natural uncultivated and unirrigated reference soil. Correlation and factor analyses showed that all determined trace elements likely originated from the same natural sources, which probably are the soil parent material and atmospheric depositions.

Description: The large dryland area of the Loess Plateau (China) is subject of developing strategies for a sustainable crop production, e.g., by modifications of nutrient management affecting soil quality and crop productivity. A 19 y long-term experiment was employed to evaluate the effects of fertilization regimes on soil organic C (SOC) dynamics, soil physical properties, and wheat yield. The SOC content in the top 20 cm soil layer remained unchanged over time under the unfertilized plot (CK), whereas it significantly increased under both inorganic N, P, and K fertilizers (NPK) and combined manure (M) with NPK (MNPK) treatments. After 18 y, the SOC in the MNPK and NPK treatments remained significantly higher than in the control in the top 20 cm and top 10 cm soil layers, respectively. The MNPK-treated soil retained significant more water than CK at tension ranges from 0 to 0.25 kPa and from 8 to 33 kPa for the 0–5 cm layer. The MNPK-treated soil also retained markedly more water than the NPK-treated and CK soils at tensions from 0 to 0.75 kPa and more water than CK from 100 to 300 kPa for the 10–15 cm layer. There were no significant differences of saturated hydraulic conductivity between three treatments both at 0–5 and 10–15 cm depths. In contrast, the unsaturated hydraulic conductivity in the MNPK plot was lower than in the CK plot at depths of 0–5 cm and 10–15 cm. On average, wheat yields were similar under MNPK and NPK treatments and significantly higher than under the CK treatment. Thus, considering soil-quality conservation and sustainable crop productivity, reasonably combined application of NPK and organic manure is a better nutrient-management option in this rainfed wheat–fallow cropping system.

Description: The aim of the present study was to evaluate the effect of cultivation of some agronomic plant species on inorganic soil-P fractions in different sampling zones. The experiment was conducted as a completely randomized design as factorial in three replicates. The factors were plant species (10 different species and control) and soil-sampling zone (soil adhering to root mat, rhizosphere soil, and nonrhizospheric soil). The thin-slicing technique was modified and used to sample rhizosphere soil. The percentages of P fractions in the planted and control soils were near 64% apatite (apatite-P), 24% octa-Ca-phosphates (OCP-P), 7% Fe-phosphates (Fe-P), 4% di-Ca-phosphates (DCP-P), 1% Al-phosphates (Al-P), and 0% occluded-P (O-P). All of the studied plant species decreased significantly all of the inorganic P fractions in soil adhering to root mat and in rhizosphere soil compared to those in nonrhizosphere soil. However, these decreases were not equal for each fraction and the percentage of apatite-P increased in rhizosphere soil of the plant species. The means of total P, soluble P, DCP-P, OCP-P, Al-P, and Fe-P were lower in soil adhering to root mat compared to those in rhizosphere soil. However, this difference was only significant for OCP-P. In contrast, the mean of apatite-P in soil adhering to root mat was significantly higher than that in rhizosphere soil. The changes of apatite-P may be more governed by microbial activities (especially mycorrhizal symbiosis) which may be higher in rhizosphere soil compared to soil adhering to root mat.

Description: Early in the 19th century, the German doctor and natural scientist Christian G. Ehrenberg (1795–1876) determined and classified through microscopic investigation the species and contents of microorganisms (bacteria, algae, diatoms, protozoa) of more than 1000 soil samples from all over the world. He identified phytoliths and minerals using a polarization microscope and described the morphology of the organic particles. Two of his soil descriptions were a Chernozem from Russia and an Ornithogenic Cryosol of the Maritime Antarctic. He further identified several soil-forming processes like the formation and decomposition of organic matter, mineral weathering, and new formation of carbonates, Fe oxides, and silicate under the influence of microorganisms long before other investigators. Although this was criticized during his time, it is still fully accepted today. Therefore, Ehrenberg can be regarded as the main founder of soil microbiology and as a pioneer in soil micromorphology.