ALBERT

Description: The present study investigates the effect of urine and ammonium nitrate on maize ( Zea mays L.) vegetative growth, leaf nutrient concentration, soil electrical conductivity, and exchangeable-cations contents under various concentrations of NaCl in a soil substrate. The experiment was arranged in a completely randomized block design with eight replications under greenhouse conditions. The experimental soil substrate was made from a 1 : 1 : 1 volume-ratio mixture of compost, quartz sand, and silty-loam soil. Salinity was induced by adding 0, 15, and 30 mL of 1 M NaCl solution per kg of substrate to achieve an electrical conductivity (EC) of 1.3 (S0), 4.6 (S1), and 7.6 (S2) dS m –1 . Nitrogen sources were urine and ammonium nitrate applied at 180 and 360 mg N (kg soil substrate) –1 . Basal P and K were added as mono potassium phosphate in amounts equivalent to 39 mg P and 47 mg K (kg substrate) –1 , respectively. In the S0 treatment, a 3-fold increase in EC was measured after urine application compared to an insignificant change in ammonium nitrate–fertilized substrates 62 d after sowing. Under saline conditions, application of 360 mg N (kg soil) –1 as urine significantly decreased soil pH and maize shoot dry weight. At the highest salt and N dose (S2, N360) 50% of urine-fertilized plants died. Regardless of salinity there was no significant difference between the two fertilizers for investigated growth factors when N was supplied at 180 mg (kg soil) –1 . Leaf N and Ca contents were higher after urine application than in ammonium nitrate–fertilized plants. At an application rate of 180 mg N (kg soil) –1 , urine was a suitable fertilizer for maize under saline conditions. Higher urine-N dosages and/or soil salinity exceeding 7.6 dS m –1 may have a deleterious effect on maize growth.

Description: The objective of this study was to investigate the effects of mono- and polyvalent cations on sorption of the two hydrophobic compounds nonylphenol (NP) and phenanthrene (Phe). To this end, exchange sites of a sandy soil were saturated with either Na + , Ca 2+ , or Al 3+ and excess salts were removed by washing. The samples were then sterilized and either stored moist, dried at room temperature, or at 20°C, 60°C, or 105°C in a vented oven. Saturation with Na + led to an increase of dissolved organic C (DOC) concentration in the soil water extracts, whereas the polyvalent cations Ca 2+ and Al 3+ decreased it. The 1 H-NMR relaxometry analyses showed that Al 3+ restricted the mobility of water molecules that are confined within the SOM structure to a higher extent than Ca 2+ or Na + . According to contact-angle (CA) analyses, cation treatment did not significantly change the wetting properties of the samples. Batch sorption–desorption experiments showed no clear salt-treatment effects on the sorption and desorption equilibria or kinetics of NP and Phe. Instead, the sorption coefficients and sorption hysteresis of NP and Phe increased in dry soil. With increasing drying temperature the CA of the soils and the sorption of both xenobiotics increased significantly. We conclude that structural modifications of SOM due to incorporation of polyvalent cations into the interphase structure do not modify the sorption characteristics of the soil for hydrophobic compounds. Instead, increasing hydrophobization of organic soil constituents due to heat treatment significantly increased the accessible sorption sites for nonpolar organic compounds in this soil.

Description: Previous pot cropping and laboratory incubation experiments were consistent with field observations showing that temporary flooding before cropping can increase the availability of soil Fe to plants. To study the effect of temporary flooding on changes in soil Fe phytoavailability we used 24 highly calcareous, Fe chlorosis–inducing soils to carry out a pot experiment where peanut and chickpea were successively grown after flooding for 30 d. At the end of the cropping experiment, the preflooded soil samples exhibited higher concentrations of acid oxalate-, citrate/ascorbate- and diethylenetriaminepentacetic acid (DTPA)–extractable Fe (Fe ox , Fe ca , and Fe DTPA , respectively) than the control (nonflooded) samples. Also, Fe ox and Fe ca exhibited no change by effect of reflooding of the cropped soils or three wetting–drying cycles in freeze-dried slurries of soils previously incubated anaerobically for several weeks. Leaf chlorophyll concentration (LCC) in both peanut and chickpea was greatly increased by preflooding. The best predictor for LCC was Fe ox , followed by Fe ca and Fe DTPA . The LCC–soil Fe relationships found suggest that the Fe species extracted by oxalate and citrate/ascorbate from preflooded soils were more phytoavailable than those extracted from control soils. However, the increased phytoavailability of extractable Fe forms was seemingly limited to the first crop (peanut). Flooding dramatically increased Fe DTPA ; however, high Fe DTPA levels did not result in high LCC values, particularly in the second crop. Therefore, this test is a poor predictor of the severity of Fe chlorosis in preflooded soils.

Description: In dry Mediterranean-type climates boron (B) levels may naturally be high and even toxic to plants. Although liming of an acidic soil is expected to decrease B levels, it is not known what the effects would be in such areas of high-B soils, especially in B-sensitive crops such as apple trees. Thus, our aim was to study the behavior of added B in newly planted apple rootstocks in an acidic soil which was limed to pH 6.5 in an outdoor pot experiment. Added B increased significantly B extractability from soil, and B levels were lower in the limed compared to the acidic soils. Plant B concentrations also increased with added B but differences between limed and unlimed soils were not evident, because plant B did not seem to reflect changes in B behavior in soil. However, B uptake was significantly increased with added B, and was further increased with liming, contrary to what the soil extractions indicated, due to improved growth conditions. Our results show that although liming decreased soil B levels, at the same time it did not affect plant B concentration and accelerated the uptake of added B, indicating a possibility for increased soil-to-plant mobility of B.

Description: Planting cover crops after corn-silage harvest could have a critical role in the recovery of residual N and N from fall-applied manure, which would otherwise be lost to the environment. Experiments were conducted at the University of Massachusetts Research Farm during the 2004–2006 growing seasons. Treatments consisted of oat and winter rye cover crops, and no cover crop, and four cover-crop dates of planting. The earliest planting dates of oat and winter rye produced the maximum biomass yield and resulted in the highest nitrate accumulation in both cover-crop species. The average nitrate accumulation for the 3 years in winter rye and oat at the earliest time of planting was 60 and 48 kg ha –1 , respectively. In 2004 where the residual N level was high, winter rye accumulated 119 kg nitrate ha –1 . While initially soil N levels were relatively high in early September they were almost zero at all sampling depths in all plots with and without cover crops later in the fall before the ground was frozen. However, in plots with cover crops, nitrate was accumulated in the cover-crop tissue, whereas in plots with no cover crop the nitrate was lost to the environment mainly through leaching. The seeding date of cover crops influenced the contribution of N available to the subsequent crop. Corn plants with no added fertilizer, yielded 41% and 34% more silage when planted after oat and rye, respectively, compared with the no–cover crop treatment. Corn-silage yield decreased linearly when planting of cover crops was delayed from early September to early or mid-October. Corn-ear yield was influenced more than silage by the species of cover crop and planting date. Similar to corn silage, ear yield was higher when corn was planted after oat. This could be attributed in part to the winter-kill of oat, giving it more time to decompose in the soil and subsequent greater release of N, while the rapidly increasing C : N ratio of rye can lessen availability to corn plants. Early plantings of cover crops increased corn-ear yield up to 59% compared with corn-ear yield planted after no cover crop.

Description: Arbuscular mycorrhizal fungi (AMF) are integral functioning parts of plant root systems and are widely recognized for enhancing plant growth on severely disturbed sites, including those contaminated with heavy metals. However, the generality of detailed patterns observed for their influence on various metals and oxidative-stress parameters in multiple plant species is not clarified. The goal of this study was to investigate the patterns of metal-stress alleviation by AMF in four plant species. For this purpose, clover, sunflower, mustard, and phacelia were inoculated with Glomus intraradices and compared to noinoculated plants grown under heavy metal–stressed conditions. The study focused on the effect of AMF inoculation on plant biomass, assimilating pigments, total protein, superoxide dismutase and peroxidase activity, lipid peroxidation and As, Cd, Co, Cu, Fe, Mn, P, Pb, U, and Zn contents. As a result of inoculation very different patterns of variation were obtained for concentrations of elements and for biochemical parameters in plants. The particular effect of AMF inoculation on plants was species- and metal-specific, although there was a general enhancement of plant growth.

Description: Precipitation and topsoil samples from a climate transect over the Scandinavian Mountains, Norway, were analyzed for bulk and compound-specific δ 18 O values. The natural abundance of 18 O in the plant-derived hemicellulose biomarkers arabinose and xylose correlates positively with δ 18 O of bulk soil, but not with δ 18 O of precipitation. This suggests that other factors than δ 18 O prec , such as evaporative 18 O enrichment of leaf water, exert a strong influence on the natural abundance of 18 O in soils.

Description: As a cover crop, buckwheat ( Fagopyrum esculentum ) may increase soil-P availability. Buckwheat was grown in low-P and P-fertilized field plots, and organic anions were measured in rhizosphere soil. Soil-P availability was not affected by buckwheat, but the concentration of rhizosphere tartrate 2– was significantly higher ( p 〈 0.005) in low-P vs. P-fertilized plots. This suggests that organic-anion root exudation may have a role in buckwheat-rhizosphere P dynamics.

Description: Intensification of weather extremes is currently emerging as one of the most important facets of climate change. Research frontiers are in analyzing (1) the consequences for the hydrological cycle and (2) the effects of multifactor scenarios on ecosystems. However, in all theoretical and experimental scenarios, challenges arise as to how precipitation regimes translate into variation in soil moisture. Here, we explore soil-moisture response to experimental changes in the precipitation regime in Central Europe over a period of 5 y, particularly focusing on the effects of recurrent extreme weather events. Intraannual difference in weekly precipitation sums imposed by extreme-drought or heavy-rainfall manipulations clearly exceeded interannual variation in the ambient precipitation pattern during the growing season between 2005 and 2009. However, soil-moisture variability in the experimental plots did not clearly reflect any altered patterns in response to the manipulated precipitation regime. Natural variation in soil moisture between years was similar to within-season differences between manipulations. Strong differences in soil-moisture dynamics during the growing season can, however, be generated by changing the temporal distribution of rainfall events while keeping the magnitude of the precipitation sum constant. Our findings confirm a common methodological dilemma in precipitation-change experiments searching for a logical way to determine how precipitation change affects communities and ecosystems on relatively short time scales: Alteration of weather regimes according to extreme-value statistics and future scenarios vs. systematic alteration of soil moisture. For Central Europe, our data suggest that other factors rather than the magnitude of rainfall exclusion or addition would appear to be decisive for ecosystem response to more extreme precipitation regimes. Response of soil moisture to frequency, return interval, and timing of events is a promising approach for further exploration. In addition, buffer capacity of the ecosystem under study has to be taken into account.

Description: Mancozeb is a fungicide frequently used in tropical countries. It rapidly decomposes into ethylenethiourea (ETU), a more stable and toxic metabolite than mancozeb that is, therefore, regarded as a pollutant of concern. The objective was to study ETU formation and decay kinetics in soil and water under tropical conditions in order to assess its potential for accumulation. Batch experiments, spiked with either mancozeb or ETU, were carried out under natural (= active) as well as tyndallized conditions. In active soils, dissipation of ETU occurred significantly faster (half-life 1.5 h) than in tyndallized soils (half-life time 28 h). In water under natural and sterile conditions, decay was slower than in soils with an ETU half-life time of 115 and 99 h, respectively. Microbial activity was seen to play an important role in ETU dissipation in soil. However, in water nonbiological processes seem to be more important in the breakdown of the molecule, with hydrolysis being the most probable decay mechanism. Decay of both mancozeb and ETU was found to occur more rapidly than previously reported. The high humidity and temperatures under the simulated humid tropical conditions, and higher microbial activity, lead to more rapid decay of these molecules than under other conditions. Nevertheless, a concentration of 1.29 mg ETU L –1 was still observed 8 d after adding mancozeb (20.83 mg L –1 ) to water under humid tropical conditions. These results suggest that, in comparable regions in the humid tropics, it is unlikely that ETU would accumulate in soil but it represents a potential risk for accumulation in water bodies.

Description: In spite of several published studies we have an incomplete understanding of the ion-release mechanisms and characteristics of polymer-coated fertilizers (PCF). Here we extend current conceptual models describing release mechanisms and describe the critical effects of substrate moisture and temperature on macro- and micronutrient release of three PCF types: Polyon®, Nutricote®, and Osmocote®. Nutrient release was quantified at weekly intervals for up to 300 d from 5°C to 40°C in water and chemically inert sand, substrates that allowed release quantification without confounding effects of ion sorption/desorption. At least two release-timeframe formulations of each PCF type were studied and all products had similar nutrient concentrations to allow isolation of the effect of coating technology. Contrary to several studies, our data and model indicate that there is no significant difference in nutrient-release rates in water and a moist, solid substrate. This means that release rates determined in water can be used to model bio-available nutrient concentrations in moist soil or soilless media where sorption/desorption properties alter concentrations after release. Across all PCF, the nutrients most affected by temperature were typically N, K, B, Cu, and Zn, while the least affected were P, Mg, and Fe. We also found consistent differences among the coating technologies. Osmocote fertilizers released faster than specified at both high and low temperatures. Nutricote had relatively steady release rates over time and a nonlinear response to temperature. Polyon released more slowly than specified but replicate samples were highly uniform.

Description: Recently, indirect evidence was obtained for inhibition of soil net N mineralization by sterols in soil organic matter, which could have been caused by their antioxidant or antimicrobial properties. The objective of this study was to test the effect of potential inhibitors ( i.e., individual compounds with known antioxidant and/or antimicrobial properties) on soil microbial mineralization processes during incubation for 7 and 14 d. A sandy agricultural soil was amended with four substances: two phenolic acids differing in their antioxidant capacity (AOC) (acetovanillone with no AOC, ferulic acid with large AOC), Trolox, an analogue of vitamin E (large AOC), and β-sitosterol (no AOC, but potential antimicrobial properties). The two compounds with large AOC (ferulic acid and Trolox) showed no significant inhibition of C and net N mineralization; and the Trolox amendment actually caused a significant increase in C and net N mineralization after 7 d of incubation. Acetovanillone with no measurable AOC caused a significant increase in C mineralization (109% of substance C added), indicating degradation of the substance, and a very pronounced negative net N mineralization within 7 d (–356%), which was interpreted as N immobilization. Only β-sitosterol showed strong inhibition of net N mineralization after 7 and 14 d (–59% and –26%, respectively) which was not interpreted as N immobilization, since there was no concomitant increase in C mineralization. Thus, an antimicrobial effect of β-sitosterol specificly on microorganisms of the N cycle was suggested, but there was no clear inhibitory effect caused by the antioxidant compounds.

Description: Sheath blight caused by Rhizoctonia solani is a major disease of rice worldwide. Silicon (Si) can enhance rice resistance to sheath blight, but the relation with phenolic metabolism is poorly known. Two rice cultivars with different levels of resistance to R. solani (resistant Teqing and susceptible Ningjing 1) were studied to determine the effects of Si on disease intensity (rated from 0 to 9) and the involvement of phenolic compounds in disease resistance. Variation in the concentrations of phenolics (including total soluble phenolics, flavonoids, and lignin) and in the activities of defense-related enzymes polyphenoloxidase (PPO) and phenylalanine ammonia-lyase (PAL) in rice leaf sheaths was investigated. The results show that Si application reduced sheath-blight disease ratings of Ningjing 1 and Teqing by 2.96 and 0.65, respectively. In uninoculated plants, Si application alone had no significant effects on the concentrations of phenolic compounds or on the activities of PPO and PAL. In inoculated plants, Si application increased phenolics concentrations and PPO and PAL activities only in the susceptible cultivar Ningjing 1. We conclude that Si-induced enhancement of phenolic metabolism contributed to the improved resistance of rice to sheath blight in the sensitive cultivar.

Description: Humus-balancing methods are simple tools for the assessment of interactions between agricultural land use and soil organic matter (SOM). Aside from this commonality, approaches for humus balancing differ considerably with regard to their specific aim, scope, and methodical approach. The term “humus balance” covers both simple models to quantify SOM change in arable soils, or soil organic C (SOC) change in particular, and models that refer to the optimization of soil productivity in arable soils by calculating organic-fertilizer demand, without quantifying SOM or SOC change. This situation naturally has caused much discussion and misunderstandings. Against this background, the aim of this review is to systematically explore the different methodical approaches to humus balancing in order to contribute to a more sophisticated discussion of this model family, its opportunities, and limitations. As humus balancing has long history as well as special actual relevance in Germany, and, lately Switzerland, we focus on these countries and discuss the different approaches that are presently available and applied there. We argue that humus balances can be roughly categorized into “ecological” and “agronomical” approaches based on their specific concepts and methodology. Ecological humus balances comprise a strong link to quantitative SOM change, while humus balances of the agronomical family refer to the maintenance of soil productivity without a quantitative link to SOM change. Lately, some models have been presented that link the two concepts. However, we identify that humus-balancing methods often are insufficiently validated, partly because the validation of agronomical humus balances is not easily possible without a very comprehensive field-experimental basis. Further, the comparability of different approaches even within the two concept families is low at present, indicating the need for a comparative model evaluation for a proper assessment of the methods.

Description: Leguminous plants grown in sewage sludge–amended soils can acquire nitrogen by assimilation of nitrate and ammonium from the soil solution or from atmospheric-dinitrogen (N 2 ) fixation through association with N 2 -fixing bacteria. We proposed that operation of both metabolic processes could contribute to alleviate the impact of drought in sludge-treated plants. A greenhouse experiment was conducted to evaluate the involvement of nodule metabolism in the use efficiency of water and N in sludge-treated plants. Treatments comprised (1) plants inoculated with rhizobia and amended with sewage sludge; (2) plants inoculated with rhizobia without any amendment; and (3) noninoculated plants supplied with ammonium nitrate, each under well-watered and drought conditions. Under drought, sludge-treated plants had increased plant growth and higher photosynthetic and water-use efficiencies than untreated plants. Drought stimulated nitrate reductase and GS/GOGAT activities but did not affect the activities of phosphoenolpyruvate carboxylase and malate dehydrogenase or the leghemoglobin concentration. The results suggest that under drought conditions, both N 2 fixation and nitrate assimilation in nodules of sludge-treated plants contributed to improve plant N supply and to increase the drought tolerance of alfalfa.

Description: Commercial fertilizers containing synthetic manganese (Mn) chelates and complexes are currently used to alleviate Mn deficiency in crops. However, studies conducted on Mn sources in order to evaluate their behavior maintaining Mn soluble in nutrient solution and soil have not been done. In this work, representative commercial Mn fertilizers based on chelates and complexes were characterized and their chemical stability in solution and interaction with soils has been evaluated. Fertilizers studied were two ethylene diamine tetraacetic acid (EDTA) Mn chelates, one N -( 1,2 -dicarboxyethyl)-D,L-aspartic acid (IDHA) Mn chelate, two lignosulfonates, one carboxylate, one fulvate, one gluconate, and one heptagluconate-based Mn complex. Characterization consisted of the determination of the soluble and chelated or complexed Mn, and the ligand identification by nuclear-magnetic resonance (NMR). Stability study included batch experiments in Ca solution at different pH and three batch experiments with soil comparing with MnSO 4 . Results indicate that most of the Mn fertilizers comply with the declared “soluble and chelated or complexed” metal content. At a usual pH range of calcareous soils (7.5–8.5), both chelates and complexes maintain more Mn in solution than MnSO 4 in the presence of Ca. Several factors affect the Mn remaining in solution after the interaction with the soil, especially, the soil-to-solution ratio. All chelates and complexes are better alternatives to the use of MnSO 4 in agronomical practices such as fertigation and soil application. Mn-IDHA as chelate and Mn-HGl or Mn-Carb as complexes can be efficient, economical, and environmental friendly fertilizers for foliar application and hydroponic cultures. In soil application, Mn-EDTA or Mn-LS would be the best options. In this case, lignosulfonic acid represents a sustainable and low-cost solution.

Description: The ability of plants to extract water from soil is controlled by the water-potential gradient between root and soil, by the hydraulic conductivity of roots, and, as the soil dries, by that of the soil near the roots (rhizosphere). Recent experiments showed that the rhizosphere turned hydrophobic after drying and it remained temporarily dry after rewetting. Our objective was to investigate whether rhizosphere hydrophobicity is associated with a reduction in root water uptake after drying and rewetting. We used neutron radiography to trace the transport of deuterated water (D 2 O) in the roots of lupines growing in a sandy soil. The plants were grown in aluminum containers (28 × 28 × 1 cm 3 ) filled with a sandy soil. The soil was initially partitioned into different compartments using a 1-cm layer of coarse sand (three vertical × three horizontal compartments). We grew plants in relatively moist conditions (0.1 〈 θ 〈 0.2). Three weeks after planting, we let the upper left compartment of soil to dry for 2–3 d while we irrigated the rest of the soil. Then, we injected D 2 O in this compartment and in the upper right compartment that was kept wet. We monitored D 2 O transport in soil and roots with time-series neutron radiography. From the changes of D 2 O concentration inside roots, we estimated the root water uptake. We found that root water uptake in the soil region that was let dry and rewetted was 4–8 times smaller than that in the region that was kept moist. The reduced uptake persisted for 〉 1–0.5 h. We conclude that a reduction in hydraulic conductivity occurred during drying and persisted after rewetting. This reduction in conductivity could have occurred in roots, in the rhizosphere, or more likely in both of them.

Description: We investigated the effects of charcoal under flooded (anoxic) rice cultivation at low and high fertilizer levels during 2 y in the Maranhão lowlands, eastern periphery of Amazonia. Two applications (at onset of first and second year) of 15 Mg ha –1 of fine (〈 2 mm) charcoal derived from the endocarp of the babassu ( Attalea speciosa Mart.) palm nut had little influence on soil fertility, rice growth, yield, and nutritional status. Exception to this were negative impacts of charcoal on first-year N availability, with lower sub-superficial soil NH availability paired with lower rice tissue N and a responsiveness of grain yields to (mainly N-) fertilization following charcoal application. This N-limitation effect was, however, limited to the first year and—though statistically significant—without agronomic relevance. The most consistent charcoal effect on flooded-soil fertility was the strong increase in K availability in the second year, at low and to a lesser extent at intermediate, but not at high fertilizer level. Low K concentrations of our charcoal exclude the possibility of direct K inputs via charcoal, suggesting other indirect mechanisms for K availability increases. Methane fluxes in the second year were significantly reduced (–43.8%) by charcoal application, charcoal-induced reductions were stronger under high- (–47.3%) than under low-fertilizer regime (–26.0%). Thus, charcoal could be a valuable tool for reducing methane emissions associated with intensely fertilized flooded rice, without significantly affecting grain yields.

Description: The aim of this study was to determine the influence of leaf-litter type ( i.e., European beech— Fagus sylvatica L. and European ash— Fraxinus excelsior L.) and leaf-litter mixture on the partitioning of leaf-litter C and N between the O horizon, the topsoil, the soil microbial biomass, and the CO 2 emission during decomposition. In a mature beech stand of Hainich National Park, Thuringia, Germany, undisturbed soil cores (∅ 24 cm) were transferred to plastic cylinders and the original leaf litter was either replaced by 13 C 15 N-labeled beech or ash leaf litter, or leaf-litter-mixture treatments in which only one of the two leaf-litter types was labeled. Leaf-litter-derived CO 2 -C flux was measured every second week over a period of one year. Partitioning of leaf-litter C and N to the soil and microbial biomass was measured 5 and 10 months after the start of the experiment. Ash leaf litter decomposed faster than beech leaf litter. The decomposition rate was negatively related to initial leaf-litter lignin and positively to initial Ca concentrations. The mixture of both leaf-litter types led to enhanced decomposition of ash leaf litter. However, it did not affect beech leaf-litter decomposition. After 5 and 10 months of in situ incubation, recoveries of leaf-litter-derived C and N in the O horizon (7%–20% and 9%–35%, respectively) were higher than in the mineral soil (1%–5% and 3%–8%, respectively) showing no leaf-litter-type or leaf-litter-mixture effect. Partitioning of leaf-litter-derived C and N to microbial biomass in the upper mineral soil (〈 1% of total leaf-litter C and 2%–3% of total leaf-litter N) did not differ between beech and ash. The results show that short-term partitioning of leaf-litter C and N to the soil after 10 months was similar for ash and beech leaf litter under standardized field conditions, even though mineralization was faster for ash leaf litter than for beech leaf litter.

Description: Global climate change affects the availability of soil nutrients, thereby influencing crop productivity. This study examined the effects of elevated [CO 2 ] and temperature on the availability of soil N and P in a paddy field in the Taihu Lake region, China. Winter wheat ( Triticum aestivum L.) was planted at two levels of atmospheric [CO 2 ] (375 μmol L –1 ambient; 575 μmol L –1 elevated) and two temperature levels (ambient and ambient + 2°C). The results were as follows: Compared to ambient, the interaction effects of elevated [CO 2 ] and temperature significantly decreased soil NH -N contents by 20.3%, 20.6%, and 18.7% in the jointing, heading, and ripening stages ( p 〈 0.05), respectively, while soil NO 3 – -N content had no clear variation trend under different [CO 2 ] and temperature conditions. Elevated [CO 2 ] significantly increased soil available P content by 14.3% in the jointing stage, and elevated temperature significantly decreased soil available P content by 18.8% in the jointing stage. Compared with ambient [CO 2 ], elevated [CO 2 ] significantly increased wheat biomass in jointing and heading stages ( p 〈 0.05). The positive effect of elevated [CO 2 ] on wheat biomass was more significant at ambient temperature (AT) than at elevated temperature (ET) in the middle and late plant growth stages. These results explained that the availability of soil N and P varied under elevated [CO 2 ] and temperature conditions. The application of N and P should be adjusted to meet the need of wheat plants after the wintering stage.

Description: Differences in soil P among silvopasture, grassland, and arable lands have been well established. Nevertheless, most of the reports compare soil properties under long-term sites. Thus, there exists little information on the effect of the conversion of silvopasture to arable or grassland use on soil P pools. The objective of the study was to determine the impact of converting silvopasture system (SP) into arable cropping and grassland system on the distribution of P pools and potential P bioavailability. We compared the following systems: SP system, SP converted to arable cropland (SP-AL), SP converted to grassland (SP-GL), and for comparative purposes, a long-term arable cropland (AL). The P fractionation was performed by a sequential extraction scheme, using acid and alkaline extractants on samples collected from the 0–10 and 10–20 cm soil layers. It was assumed that the large variations in soil-P fractionations are caused by the different management practices associated with land conversion. The results of P fractionation showed a dominance of calcium-bound P, HCl-extractable Pi constituted up to 36% of the soil total P (TP). However, the type of land use did not affect this P fraction. On the other hand, the reduction in labile-P i and NaOH-P i fractions observed at the SP-AL site may have led to the decline in readily available P. The soil total organic P (TP o ) content was 8% and 17% lower at SP-AL compared to SP and SP-GL site, respectively. Labile organic-P (labile-P o ) content was markedly higher at SP site compared to arable soils, and was ≈ 10% of TP o . The NaOH-P o constituted the highest fraction of the organic-P pool (55%–79% of TP o ) across all the study systems, and was positively correlated with TP o ( p 〈 0.01). The study indicates that conversion of SP system in temperate regions to arable cropping with conventional tillage seems to result in the reduction of P availability compared to SP, indicating SP as an important land-use practice.

Description: The influence of biochar amendments on the physical quality of a clayey soil (Vertisol) was evaluated by aggregate-size distribution and stability, water retention, and pore-space structure of biochar-amended soils. Clayey soil was treated with three kinds of biochars (straw biochar, woodchips biochar, and wastewater-sludge biochar) at the rate of 0, 20, 40, and 60 g biochar (kg soil) –1 and incubated for 180 d in glasshouse. The application of straw biochar (SB) and wastewater-sludge biochar (WSB) significantly enhanced the formation of 5–2 and 0.25–0.5 mm macroaggregates in the clayey soil relative to the control treatment, while the 〈 0.25-cm microaggregate decreased with biochar additions. However, woodchips biochar (WCB) had no obvious effect on the formation of macroaggregate. The application of SB and WSB increased the mean weight diameter (MWD) and geometric mean diameter (GMD) of clayey soil, implying that biochar increased the aggregate stability. They improved the aggregate stability through an enhanced resistance to slaking and increased interparticular cohesion. The SB-amended soils exhibited significant increases in the available water contents of soils. The application of SB significantly increased pore volume in the macropore (〉 75 μm) and mesopore (30–75 μm) ranges, which may be the result of the reorganization of pore-size distribution and aggregation processes induced by the addition of biochar. Results indicated that biochar had the potential to improve the physical quality and pore-space status of clayey soil. It is suggested that biochar may be considered as a soil amendment for improving poor physical characteristics of clayey soil.

Description: Soil drought influences the C turnover as well as the fine-root system of tree saplings. Particularly during the period of establishment, the susceptibility to drought stress of saplings is increased because of incompletely developed root systems and reduced access to soil water. Here, we subjected beech saplings ( Fagus sylvatica L.) to different levels of drought stress. Beech saplings were planted in rhizotrons, which were installed in the soil of a Norway spruce forest before bud burst. Soil moisture was manipulated in the following year during May to September. We measured photosynthetic net CO 2 uptake, volume production of fine roots, and rhizosphere respiration during the growing season. Biometric parameters of the fine-root system, biomass, and nonstructural carbohydrates were analyzed upon harvest in October. Photosynthesis and rhizosphere respiration decreased with increasing drought-stress dose (cumulated soil water potential), and cumulative rhizosphere respiration was significantly negatively correlated with drought-stress dose. Fine-root length and volume production were highest at moderate soil drought, but decreased at severe soil drought. The proportion of fine-roots diameter 〈 0.2 mm and the root-to-shoot ratio increased whereas the live-to-dead ratio of fine roots decreased with increasing drought-stress dose. We conclude that the belowground C allocation as well as the relative water-uptake efficiency of beech saplings is increased under drought.

Description: Rice growth and its resistance to pests had been often constrained by soil-silicon (Si) availability. The purpose of this study was to assess the potential of biochar soil amendment (BSA) to improve Si availability in paddy soils. A cross-site field trail with BSA was conducted in six locations with different climatic and crop-production conditions across S China. Plant-available Si content before field-trials establishment and after rice harvest, as well as Si content in rice shoot were determined. Varying with site conditions, plant-available Si content of soil was observed to increase significantly with BSA in most sites. Significant increase in rice shoot Si was detected in four out of the six sites, which was well correlated to the concurrent increase in soil pH under BSA treatment. This study demonstrates an important role of BSA to improve Si availability and uptake by rice mainly through increasing soil pH of the acid and slightly acid rice soils.

Description: The objective of this work was to study the effect of root and foliar application of two commercial products containing amino acids from plant and animal origin on iron (Fe) nutrition of tomato seedlings cultivated in two nutrient media: lime and normal nutrient solutions. In the foliar-application experiment, each product was sprayed with 0.5 and 0.7 mL L –1 2, 7, 12, and 17 d after transplanting. In the root application experiment, 0.1 and 0.2 mL L –1 of amino acids products were added to the nutrient solutions. In both experiments, untreated control plants were included as well. Foliar and root application of the product containing amino acids from animal origin caused severe plant-growth depression and nonpositive effects on Fe nutrition were found. In contrast, the application of the product from plant origin stimulated plant growth. Furthermore, significantly enhanced root and leaf Fe III -chelate reductase activity, chlorophyll concentration, leaf Fe concentration, and Fe II : Fe ratio were found in tomato seedlings treated with the product from plant origin, especially when the amino acids were directly applied to the roots. These effects were more evident in plants developed under lime-induced Fe deficiency. The positive results on Fe uptake may be related to the action of glutamic acid, the most abundant amino acid in the formulation of the product from plant origin.

Description: An in situ determination of biological soil-crust stability was carried out in two study sites along a sharp rainfall gradient. Penetration resistance (PR) of the crusts was measured using a newly developed light-weight needle-type electronic micropenetrometer. The depth-related PR data revealed two sections possessing different structures and stability. The topcrust (0–2 mm) had significantly higher amounts of N, organic C, carbonates, and salts as compared to the underlain subcrust. The mean PR of the topcrust was 0.68 MPa for the southern study site, Nizzana-South (≈ 100 mm annual rainfall), and it increased significantly for the northern study site, Nizzana-69 (≈ 170 mm annual rainfall), with a mean of 1.11 MPa. A subcrust (2–30 mm) was identified that was characterized by a high amount of carbonates and a PR 〉 2 MPa. The electronic micropenetrometer system is a promising device for identifying areas of changing crust stability in relation to biological soil-crust properties. The overall stability of biological soil crusts depends on the topcrust and subcrust structure. This structure is linked to abiotic and biotic factors and likely in relation to the amount of annual precipitation.

Description: A greenhouse experiment was carried out to determine copper (Cu) desorption characteristics in ten bulk and rhizosphere soils (Typic Calcixerepts) amended with sewage sludge (1% w/w) using rhizoboxes. The kinetics of Cu desorption in the bulk and the rhizosphere soils were determined after successive extraction with DTPA-TEA and 10 mM citric acid in a period of 1 to 504 h at (25 ± 1)°C. The results show that Cu extracted after 504 h using DTPA-TEA were significantly ( P 〈 1%) lower in the rhizosphere than the bulk soils. However, Cu extracted after 504 h using citric was significantly ( P 〈 1%) higher in the rhizosphere than in the bulk soils. The results illustrated that, on average, citric acid extracted 56% more Cu from the bulk soils than DTPA-TEA, and citric acid extracted 85% more Cu from the rhizosphere soils than DTPA-TEA. Desorption kinetics of Cu in the two extractants was well described by power-function, parabolic diffusion, and first-order equations. The results show that a 10 mM citric acid extractant may be recommended to determine the kinetics of Cu desorption in calcareous soils amended with sewage sludge.

Description: The capacity of a plant to take up chemical elements is measured as the ratio of the element concentration in the plant and its concentration in the soil. This ratio is called the bioaccumulation index (BAC). The choice of rootstock and variety can differentially affect nutrient uptake of grapevine ( Vitis vinifera L.). Generally, only slight differences can be observed in the accumulation of N, P, and Zn. In contrast, wide variations are found in the absorption of K, Ca, Mg, and Cl. While studies on plant nutrients and major elements have been carried out in vineyards, very few references concern the trace-element concentrations in leaves. In the study described here, five varieties (Airén, Cencibel, Garnacha, Cabernet Sauvignon, and Chardonnay) grown on a Calcisol Petric or Typic Calcixerept (typical of La Mancha) were compared in terms of leaf trace-element concentrations. A total of three samples (20 healthy and completely developed leaves from the middle part of the shoot) were collected from three different plants of the same variety. Leaves were dried, milled, and x-ray fluorescence analysis was performed. It was found that the variety of grapevine influences the uptake of four of the major elements: Al (low in Garnacha, [0.4 ± 0.2] g kg –1 ), Ca (high in Cencibel, [32.6 ± 8.1] g kg –1 ), P (low in Airén, [0.9 ± 0.4] g kg –1 ) and K, which showed significant differences in almost all of the varieties (from [4.7 ± 1.8] g kg –1 in Cencibel to [8.0 ± 10.1] g kg –1 in Chardonnay). No statistically significant varietal differences were found for trace elements. The only exception was La, which was present at higher levels in the variety Cencibel ([7.5 ± 0.3] mg kg –1 ). This finding allows to assess the geochemical fingerprinting of calcareous soils regardless of the grapevine variety studied.

Description: The use of biochar as a soil amendment is gaining interest to mitigate climate change and improve soil fertility and crop productivity. However, studies to date show a great variability in the results depending on raw materials and pyrolysis conditions, soil characteristics, and plant species. In this study, we evaluated the effects of biochars produced from five agricultural and forestry wastes on the properties of an organic-C-poor, slightly acidic, and loamy sand soil and on sunflower ( Helianthus annuus L.) growth. The addition of biochar, especially at high application rates, decreased soil bulk density and increased soil field capacity, which should impact positively on plant growth and water economy. Furthermore, biochar addition to soil increased dissolved organic C (wheat-straw and olive-tree-pruning biochars), available P (wheat-straw biochar), and seed germination, and decreased soil nitrate concentration in all cases. The effects of biochar addition on plant dry biomass were greatly dependent upon the biochar-application rate and biochar type, mainly associated to its nutrient content due to the low fertility of the soil used. As a result, the addition of ash-rich biochars (produced from wheat straw and olive-tree pruning) increased total plant dry biomass. On the other hand, the addition of biochar increased the leaf biomass allocation and decreased the stem biomass allocation. Therefore, biochar can improve soil properties and increase crop production with a consequent benefit to agriculture. However, the use of biochar as an amendment to agricultural soils should take into account its high heterogeneity, particularly in terms of nutrient availability.

Description: Cynodon dactylon (L.) Pers. is a perennial rhizomatous grass (Poaceae), grown for cattle nutrition on the riverbanks of Río Tinto (Southwest Iberian Peninsula, Spain), a highly acidic area with high concentrations of iron (Fe) and other metals. This study focuses on the absorption, distribution, and accumulation of Fe in the root, rhizome, and leaves of C. dactylon under controlled conditions. Plants collected from Río Tinto were grown in a Hoagland solution containing 500 mg kg –1 of ferrous Fe. Samples were collected up to 2 months after exposure and analyzed for total Fe concentration using inductively coupled plasma–mass spectrometry (ICP-MS) and for Fe distribution and bioformations by scanning electron microscopy (SEM) with an energy-dispersive x-ray analyzer (EDX). The results show high concentrations of Fe in all plant organs, with fast Fe translocation from roots to leaves. Iron bioformations composed mainly of Fe, S, and K were detected in all plant organs and were especially apparent in roots and leaves. These results differ from those reported for another species of Poaceae, Imperata cylindrica , which grows under the same environmental conditions, suggesting the existence of different resistance strategies between species of the same family.

Description: A better understanding of the impact of fertilizer nitrogen (N) on biomass and N accumulation, and their partitioning into different plant components is needed to optimize crop yield and quality. A field experiment with spring wheat ( Triticum aestivum ), hulless ( Avena nuda ), and hulled ( Avena sativa ) oats was conducted for 3 years in Ottawa, ON, Canada, to determine the crop responses to N addition (0, 75, and 150 kg N ha –1 ). Biomass, N, and phosphorus (P) accumulation and partitioning into different plant components were examined during the growth season. Lodging score was determined for all crops when it occurred and again at harvest. During the growth season, both hulless and hulled oats and the wheat cultivar showed almost similar patterns of N and P accumulation with maximum contents at late grain filling or at harvest. Plant N concentration was up to 60 g kg –1 during the seedling stage, decreased gradually with advancing growth stages, and was lowest at harvest. Nitrogen treatments significantly increased plant N and P contents. At heading stage, N treatments enhanced dry matter (24%–45%), N (35%–135%), and P (27%–45%) contents in plant components ( i.e., culm, leaf, and head), but also enhanced crop lodging, especially in oats. Both hulled and hulless oats had higher total plant N (5%–35%), N : P ratio, and dry-matter content in leaf (6%–43%) and head (0%–129%) along with higher P (up to 27%) in culm than the wheat cultivar. The wheat cultivar accumulated greater dry matter and higher N content in kernels than both hulled and hulless oats at harvest. Both hulled and hulless oat cultivars exhibited similar lodging susceptibility to N addition (75 or 150 kg N ha –1 ), produced lower dry weight and lower kernel N, and hence lower grain yield than the wheat cultivar. The larger vegetative dry-matter accumulation at heading coupled with higher P content in culms under high-N-supply conditions may be related to severe lodging in oat cultivars.

Description: Biochar (BC) application as a soil amendment has aroused much interest and was found to considerably improve soil nutrient status and crop yields on poor, tropical soils. However, information on the effect of BC on temperate soils is still insufficient, with effects expected to differ from tropical soils. We investigated the effects of BC on soil nutrient dynamics, crop yield, and quality in a greenhouse pot experiment. We compared three agricultural soils (Planosol, Cambisol, Chernozem), and BCs of three different feedstocks (wheat straw [WS], mixed woodchips [WC], vineyard pruning [VP]) slowly pyrolyzed at 525°C, of which the latter was also pyrolyzed at 400°C. The BCs were applied at two rates (1% and 3%, which would correspond to 30 and 90 t ha –1 in the field). Three crops, namely mustard ( Sinapis alba L.), barley ( Hordeum vulgare L.), and red clover ( Trifolium pretense L.) were grown successively within one year. The investigated soil properties included pH, electrical conductivity (EC), cation-exchange capacity (CEC), calcium-acetate-lactate (CAL)–extractable P (P CAL ) and K (K CAL ), C, N, and nitrogen-supplying potential (NSP). The results show a pH increase in all soils. The CEC increased only on the Planosol. The C : N ratio increased at 3% application rate. Despite improving the soil nutrient status partly, yields of the first crop (mustard) and to a lesser extent of the second crop (barley) were significantly depressed through BC application (by up to 68%); the yield of clover as third crop was not affected. Only the BC from WS maintained yields in the range of the control and even increased barley yield by 6%. The initial yield reduction was accompanied by notable decreases (Cu, Fe, Mn, Zn) and increases (Mo) in micronutrient concentrations of plant tissues while nitrogen concentrations were hardly affected. The results of the pot experiment show that despite additional mineral fertilization, short-term growth inhibition may occur when applying BC without further treatment to temperate soils.

Description: To improve soil structure and take advantage of several accompanying ecological benefits, it is necessary to understand the underlying processes of aggregate dynamics in soils. Our objective was to quantify macroaggregate (〉 250 μm) rebuilding in soils from loess (Haplic Luvisol) with different initial soil organic C (SOC) contents and different amendments of organic matter (OM) in a short term incubation experiment. Two soils differing in C content and sampled at 0–5 and 5–25 cm soil depths were incubated after macroaggregate destruction. The following treatments were applied: (1) control (without any addition), (2) OM 1 (addition of OM: preincubated wheat straw [〈 10 mm, C : N 40.6] at a rate of 4.1 g C [kg soil] –1 ), and (3) OM 2 (same as (2) at a rate of 8.2 g C [kg soil] –1 ). Evolution of CO 2 released from the treatments was measured continuously, and contents of different water-stable aggregate-size classes (〉 250 μm, 250–53 μm, 〈 53 μm), microbial biomass, and ergosterol were determined after 7 and 28 d of incubation. Highest microbial activity was observed in the first 3 d after the OM application. With one exception, 〉 50% of the rebuilt macroaggregates were formed within the first 7 d after rewetting and addition of OM. However, the amount of organic C within the new macroaggregates was ≈ 2- to 3-fold higher than in the original soil. The process of aggregate formation was still proceeding after 7 d of incubation, however at a lower rate. Contents of organic C within macroaggregates were decreased markedly after 28 d of incubation in the OM 1 and OM 2 treatments, suggesting that the microbial biomass (bacteria and fungi) used organic C within the newly built macroaggregates. Overall, the results confirmed for all treatments that macroaggregate formation is a rapid process and highly connected with the amount of OM added and microbial activity. However, the time of maximum aggregation after C addition depends on the soil and substrate investigated. Moreover, the results suggest that the primary macroaggregates, formed within the first 7 d, are still unstable and oversaturated with OM and therefore act as C source for microbial decomposition processes.

Description: Rice is a Si-accumulator plant whereby Si has physio-chemical functions for plant growth. Its straw contains high shares of plant silica bodies, so-called phytoliths and can, when returned to the soil, be an important Si fertilizer. Release of Si from phytoliths into soil solution depends on many factors. In order to improve prognosis of availability and management of Si located in phytoliths, in this study we analyzed the effect of pretreatment of rice straw by dry and wet ashing and the soil-solution composition on Si release. Dry ashing of rice straw was performed at 400°C, 600°C, and 800°C and wet ashing of the original straw and the sample from 400°C treatment with H 2 O 2 . To identify the impact of soil-solution chemistry Si release was measured on separated phytoliths in batch experiments at pH 2–10 and in presence of different cations (Na + , K + , Mg 2+ , Ca 2+ , Al 3+ ) and anions (Cl – , NO , SO , acetate, oxalate, citrate) in the concentration range from 0.1 to 10 mmol c L –1 . After burning rice straw at 400°C, phytoliths and biochar were major compounds in the ash. At an electrolyte background of 0.01 mol c L –1 , Si released at pH 6.5 was one order of magnitude higher than at pH 3, where the zeta potential (ζ) was close to zero. Higher ionic strength tended to suppress Si release. The presence of cations increased ζ, indicating the neutralization of deprotonated Si-O – sites. Monovalent cations suppressed Si release more strongly than bivalent ones. Neutralization of deprotonated Si-O – sites by cations might accelerate polymerization, leading to smaller Si release in comparison with absences of electrolytes. Addition of Al 3+ resulted in charge reversal, indicating a very strong adsorption of Al 3+ , and it is likely that Si-O-Al-O-Si bonds are formed which decrease Si release. The negative effect of anions on Si release in comparison with deionized H 2 O might be due to an increase in ionic strength. The effect was more pronounced for organic anions than for inorganic ones. Burning of rice straw at low temperatures ( e.g., 400°C) appears suitable to provide silicon for rice in short term for the next growing season. High inputs of electrolytes with irrigation water and low pH with concomitant increase of Al 3+ in soil solution should be avoided in order to keep dissolution rate of phytoliths at an appropriate level.

Description: Bone char is a potential clean and renewable P fertilizer with Cd-immobilization capabilities, but the P–Cd interactions in cropping of vegetable, grain, and tuber crops are unknown. In the present pot experiment bone char was evaluated on its effect on the growth and P supply of various crops (lettuce, wheat, potatoes) as well as its capability to reduce the uptake of Cd from a moderately Cd-contaminated and P-deficient soil (soil 1) and a highly Cd-contaminated soil with sufficient P supply (soil 2). When averaging the dry-matter yield over the treatments for each crop for the P-sufficient soil 1, the following order was obtained: triple superphosphate (TSP) 〉 diammonium phosphate (DAP) 〉 BC, whereas for the soil 2 with sufficient P supply it was inverted with BC 〉 DAP 〉 TSP. The P-deficiency resulted in a more pronounced effect of TSP and DAP on the plant growth, whereas P sufficiency in the soil promoted a crop-quality-enhancing effect of bone char. The Cd concentration in the consumption-relevant plant parts was mostly insignificantly affected by treatments; however, the total Cd concentration in the whole plants tended to decrease with fertilizer addition for all crops in soil 1 even at very low bone-char application levels. Similar results were obtained for soil 2 with an exception for the Cd concentration in potatoes, as the total Cd concentration was significantly increased in the TSP and DAP treatments. This most likely results from the introduction of Cd with TSP and DAP as they contained ≈ 27–28 mg Cd kg –1 . Thus, this study demonstrated the potential of bone char as a clean P fertilizer, which can efficiently decrease the Cd contamination of potato on contaminated soils.

Description: The water balance of a certain soil profile in a certain time interval is subjected to changes of soil water content within the respective profile, and fluxes at its upper and lower boundary. Weighing lysimeters are valuable instruments for water-balance studies. Typically, mass changes—thus, changes of soil profile water content—are detected by a weighing system, while seepage water outflow is measured by a tipping bucket, and precipitation data originate from a rain gauge. Hence, evapotranspiration as unknown component can be determined by solving a simple water-balance equation. However, using separately measured precipitation data may cause implausible (negative) evapotranspiration. In this study, change of soil profile water content, seepage water, precipitation, and evapotranspiration were determined directly from 10-min lysimeter data from 2011. Precipitation measured with the lysimeter was in total 20% greater than rain-gauge values. Even dew formation was measured and considered as water-balance component; however, its total amount was rather low. Evapotranspiration calculated on daily and hourly base indicated a sound correlation with measured data, but measured values were considerably smaller. Both calculated and measured dew amount were of the same magnitude. Comparison of lysimeter evapotranspiration with daily calculations (neglecting dew) and hourly computation (considering dew) delivered similar results. Generally, the utilized lysimeter facility and the specific data management provided sound water-balance components with high accuracy and temporal resolution, respectively.

Description: In the highlands of Madagascar, agricultural expansion gained on grasslands, and cropping systems based on direct seeding with permanent vegetation cover are emerging as a means to sustain upland crop production. The objective of this study was to examine how such agricultural practices affect greenhouse-gas emissions from a loamy Ferralsol previously used as a pasture. We conducted an experiment under controlled laboratory conditions combining cattle manure, crop residues (rice straw), and mineral fertilizers (urea plus NPK or di-NH 4 -phosphate) to mimic on-field inputs and examined soil CO 2 and N 2 O emissions during a 28-d incubation at low and high water-filled pore space (40% and 90% WFPS). Emissions of N 2 O from the control soil , i.e., soil receiving no input, were extremely small (〈 5 ng N 2 O-N (g soil) –1  h –1 ) even under anaerobic conditions. Soil moisture did not affect the order of magnitude of CO 2 emissions while N 2 O fluxes were up to 46 times larger at high soil WFPS, indicating the potential influence of denitrification under these conditions. Both CO 2 and N 2 O emissions were affected by treatments, incubation time, and their interactions. Crop-residue application resulted in larger fluxes of CO 2 but reduced N 2 O emissions probably due to N immobilization. The use of di-NH 4 -phosphate was a better option than NPK to reduce N 2 O emissions without increasing CO 2 fluxes when soil received mineral fertilizers. Further studies are needed to translate the findings to field conditions and relate greenhouse-gas budgets to crop production.

Description: Although there is evidence for a positive involvement of the antioxidant defense system in plant response to salt stress, there is poor information regarding the influence of mycorrhizal symbiosis on enzymatic and nonenzymatic antioxidant defense in wheat under saline conditions. The present article focuses on the contribution of mycorrhizae to antioxidant defense in salt-stressed wheat plants. Two wheat ( Triticum aestivum L.) cultivars, Sids 1 and Giza 168, were grown under nonsaline or two saline conditions (4.7 and 9.4 dS m –1 ) with and without arbuscular mycorrhizal fungi (AMF) inoculation. Salt stress considerably decreased root colonization and plant productivity, particularly in Giza 168. Interestingly, mycorrhizal colonization alleviated the adverse effect of salt stress and significantly enhanced plant productivity, especially in Sids 1. The concentration of glycinebetaine, the activities of antioxidative enzymes (superoxide dismutase, peroxidase, catalase, and glutathione reductase) and the concentrations of antioxidant molecules (glutathione and ascorbate) were increased under saline conditions; these increases were more significant in salt-stressed mycorrhizal plants, especially in Sids 1. Salt stress induced oxidative damage through increased lipid peroxidation, electrolyte leakage, and hydrogen peroxide concentration, particularly in Giza 168. Mycorrhizal colonization altered plant physiology and significantly reduced oxidative damage. Elimination of reactive oxygen species (ROS) can be one of the mechanisms how AMF improve wheat adaptation to saline soils and increase its productivity.

Description: In a greenhouse experiment, Medicago sativa was grown in iron-rich soil colonized with iron-reducing bacteria (IRB) and/or Glomus mosseae (GM) under different inorganic phosphorus levels, which was to understand the effects of IRB and GM on the activation and turnover of the Fe(III)-fixed phosphorus. The results showed that at the both P rates, dual-inoculation treatment stimulated the hyphal growth and increased the shoot P content. IRB could accelerate mycorrhizal colonization, and showed a positive effect on plant biomass and P uptake at both P levels. Compared to sole-IRB or GM treatment, the dual inoculation treatment increased the soil available P content at both P rates ( p 〈 0.05), which was in the following order: the dual IRB+GM 〉 the sole IRB 〉 the sole GM 〉 control for soil SMP content at low P rate, whilst the dual IRB+GM 〉 the sole IRB ≈ the sole GM 〉 control treatment at high P rate. Compared with the IRB treatment, the GM treatment significantly decreased the soil available P content and the MBP content at low P rate, but made no difference at high P rates. The soil MBC in dual-inoculation treatment was greatest under the high P level, while the highest soil MBC was the sole-GM treatment under the low P level. The sole GM treatment showed significantly ( p 〈 0.05) higher soil MBC than that of sole IRB at low P rate ( p 〈 0.05), while there was no significant differences between sole IRB and sole GM at high P rate. Our results suggested that the interaction between GM and IRB had synergetic effect on the mobilization of Fe(III)-fixed P and their relationship could be regulated by the turnover of MBP. The fact that plants acquired more P via mycorrhizal pathway in the GM-IRB system suggested that the three symbiont of plant-GM-IRB had great ecological and functional significance for P activity in tropical and subtropical soil.

Description: Recent development in canopy optical-sensing technology provides the opportunity to apply fertilizer variably at the field scale according to spatial variation in plant growth. A field experiment was conducted in Ottawa, Canada, for two consecutive years to determine the effect of fertilizer nitrogen (N) input at variable- vs. uniform-application strategies at the V6–V8 growth stage, on soil mineral N, canopy reflectance, and grain yield of maize ( Zea mays L.). The variable N rates were calculated using an algorithm derived from readings of average normalized difference vegetation index (NDVI) of about 0.8 m × 4.6 m, and N fertilizer was then applied to individual patches of the same size of NDVI readings (0.8 m × 4.6 m) within a plot (2184 m 2 ). Canopy reflectance, expressed as NDVI, was monitored with a hand-held spectrometer, twice weekly before tasseling and once a week thereafter until physiological maturity. Soil mineral N (0–30 cm depth) was analyzed at the V6 and VT growth stages. Our data show that both variable and uniform-application strategies for N side-dressings based on canopy-reflectance mapping data required less amount of N fertilizer (with an average rate of 80 kg N ha –1 as side-dressing in addition to 30 kg N ha –1 applied at planting), and produced grain yields similar to and higher nitrogen-use efficiency (NUE) than the preplant fully fertilized (180 kg N ha –1 ) treatment. No difference was observed in either grain yield or NUE between the variable- and uniform-application strategies. Compared to unfertilized or fully fertilized treatments, the enhancements in grain yield and NUE of the variable-rate strategy originated from the later N input as side-dressing rather than the variation in N rates. The variable-rate strategy resulted in less spatial variations in soil mineral N at the VT growth stage and greater spatial variations in grain yield at harvest than the uniform-rate strategy. Both variable- and uniform-application strategies reduced spatial variations in soil mineral N at the VT stage and grain yield compared to the unfertilized treatment. The variable-rate strategy resulted in more sampling points with high soil mineral N than the uniform-rate strategy at the VT stage.

Description: Tea is one of the major cash crops in the tropical and subtropical areas of China. Insufficient potassium (K) supply is an important limiting factor to the productivity as the soils are highly leached and strongly acidic. However, information about effects of K fertilization and application techniques is very limited. This manuscript summarizes results of field experiments investigating K uptake, soil K status, effects and methods of K fertilization in China during the past two decades. The K stocks and uptake were investigated by soil sampling in plantations aged 1, 2, 3, 5, and 10 years. There was no harvest of young shoots, and most K was assigned to frame growth accounting for 59%–61% of the total uptake in the aboveground plant parts of young plantations aged 1–3 years. In plantations (≥ 5 years) such assignment to frame growth became relatively small (7.6%–11.9%) and a major proportion was assigned to young shoots accounting for up to 78% of the total. Analysis of 3396 soil samples taken in 2009–2010 from 54 counties of 16 main tea-producing provinces showed that the exchangeable K (extracted by Mehlich III) in soils averaged 81 mg kg –1 and in about 74% samples were below critical deficient level (100 mg kg –1 ). The low activity ratio at equilibrium ( AR  k e ) and nonspecific absorbed-K (ΔK 0 ) values of quantity-intensity ( Q / I ) curves also indicated low status of labile K pools of tea soils. Field experiments at 16 of total 18 sites with black, green, and oolong teas during 1992–2002 showed a significant increase of yield after K application either as potassium sulfate (K 2 SO 4 ) or potassium chloride (KCl) despite of the largely different initial soil exchangeable K contents, plucking standards, and yield levels among the tea types. The agronomical efficiency of K fertilizers was averaged at 8.8 kg fresh shoots or 1.71 kg tea per kg K fertilizer. The quality of harvested shoots was improved by K-fertilizer application as revealed by increased concentrations of free amino acids, water-extractable dry matter, and total polyphenols. There was little difference in the effects of K as K 2 SO 4 and KCl on yield and quality. Field experiments at six sites evaluating variable K amounts demonstrated that the optimal K doses ranged from 124 to 160 kg K ha –1 y –1 for both K 2 SO 4 and KCl and were little affected by initial soil K contents, tea types, and the yield levels. No privilege of K applications split into three times in tea seasons was observed concerning the risk of leaching in the soils of low cation-exchange capacity and abundant rainfall in the production areas. A single K application as base fertilizer in autumn had similar or better effect. The present studies showed low soil labile K pools, incapable to meet plant K demand for quality tea production, highlighting the importance of K-fertilizer application.

Description: Potassium (K) plays a major role in the basic functions of plant growth and development. In addition, K is also involved in numerous physiological functions related to plant health and resistance to biotic and abiotic stress. However, K deficiency occurs widely resulting in poor growth, lost yield, and reduced fiber quality. This review describes the physiological functions of K and its role in stress relief and also provides some agronomic aspects of K requirements, diagnosis of soil and plant K status, and amelioration. The physiological processes described include enzymes and the regulation of organic-compound synthesis, water relations and stomates, photosynthesis, transport, cell signaling, and plant response to drought stress, cold stress, salt stress, as well as biotic stresses. The agronomic aspects of K fertilization include the K requirements of cotton, K uptake, and soil characteristics, genotypic variation in K uptake and use, and characteristics of K deficiency in cotton. In addition, diagnosis and amelioration of K soil and plant status is discussed.

Description: Potassium (K) is an important nutrient for watermelon ( Citrullus lanatus Thunb. Matsum. & Nakai). However, there is little knowledge about genetic variations in K efficiency in watermelon. Sixty-four watermelon genotypes were grown under conditions of ample (6 mM) and limited (0.1 mM) K supply in a glasshouse. Thirty-eight wild genotypes ( C. lanatus var. citroide ) and 26 domesticated genotypes ( C. lanatus var. lanatus ) were cultivated hydroponically for 30 d. Shoot dry weight, shoot K concentration, K uptake, K-use index (shoot dry weight / shoot K concentration), relative shoot dry weight (shoot dry weight under limited K / shoot dry weight under ample K), and relative shoot K concentration (shoot K concentration under limited K / shoot K concentration under ample K) were determined. Significant differences were observed among genotypes. The K efficiency was classified based on a medium-efficiency interval which is equivalent to the 95% confidence interval of the mean relative shoot dry weight and relative shoot K concentration. Genotypic data above or below this interval were classified as either K-efficient or K-inefficient. We identified eight K-efficient genotypes, of which four were wild types. Thus, wild watermelons can be used in breeding programs to improve the K efficiency of domesticated watermelons.

Description: Biogas plants in Germany are producing an increasing amount of biogas residues to be recycled via agricultural crop production. To test whether the wide range of various substrates used in the anaerobic digestion can affect the chemical composition and nutrient availability, seven biogas residues derived from different substrates were investigated with respect to their N supply to ryegrass. Both the short-term and the long-term N availability were studied in a 309-d pot experiment lasting for five successive growth cycles each starting with a fertilizer application. The organic fertilizers were applied based on an equal amount of ammonium-N (300 mg N per pot) and compared to mineral N from ammonium nitrate of equal dosage. Biogas residues varied greatly in their chemical composition (ammonium-N 0.20% to 0.51%, N total 0.36% to 0.75%, and C org 1.85% to 4.75% in fresh matter). After the first growth cycle, the N availability of the biogas residues applied based on ammonium-N was at least equal to that from ammonium nitrate. Differences in N offtake after one fertilizer application were negatively correlated to the C org : N org ratio of the organic fertilizers. After five successive fertilizer applications, the N utilization of most of the organic fertilizers was increased compared to that of the mineral fertilizer. It is concluded that biogas residues provide plant-available N at least corresponding to their ammonium content and that the accumulation of organic N in soil through repeated application of biogas residues contributes to N release.

Description: The impact of horticultural management on carbon sequestration in soils has been limited so far to tillage and nitrogen fertilization. Our objective was to evaluate by mathematical modeling the effect of potassium fertilization on CO 2 binding in cropland soils. The developed model integrates three subunits: (1) A published simulator of crop dry-matter (DM) production in response to N, P, K fertilization, but not DM partitioning; (2) a published soil–crop–atmosphere model predicting crop yield and DM partitioning as a function of N but not K fertilization; (3) an original model computing the organic-inorganic carbon transformations, inorganic-carbon reactions and transport in soil, CO 2 diffusion, and soil carbon sequestration. The model described the K-fertilization effect on C binding in soil as a function of the soil pH, the Ca 2+ concentration in the soil solution, hydraulic properties, air temperature, and crop DM production, and partitioning characteristics. In scenarios of corn ( Zea mays L.) growth in clayey soil and wheat ( Triticum aestivum L.) in loam soil, the computed K-induced CO 2 sequestration amounted to ≈ 14.5 and 24 kg CO 2 (kg K) –1 , respectively (0 vs. 100 kg ha –1 K application). The soil CO 2 sequestration declined by 8% when corn grew in sandy instead of clayey soil and by 20% when the temperature was 10°C higher than the temperature prevailing in mild semiarid zones. All predicted CO 2 -sequestration results were approximately 30-fold higher than the 0.6 kg CO 2 emitted per kg of K manufactured in industry.

Description: To avoid loss of yield, crops must maintain tissue potassium (K) concentrations above 5–40 mg K (g DM) –1 . The supply of K from the soil is often insufficient to meet this demand and, in many agricultural systems, K fertilisers are applied to crops. However, K fertilisers are expensive. There is interest, therefore, in reducing applications of K fertilisers either by improving agronomy or developing crop genotypes that use K fertilisers more efficiently. Agronomic K fertiliser use efficiency is determined by the ability of roots to acquire K from the soil, which is referred to as K uptake efficiency (KUpE), and the ability of a plant to utilise the K acquired to produce yield, which is referred to as K utilisation efficiency (KUtE). There is considerable genetic variation between and within crop species in both KUpE and KUtE, and chromosomal loci affecting these characteristics have been identified in Arabidopsis thaliana and several crop species. Plant traits that increase KUpE include (1) exudation of organic compounds that release more non-exchangeable soil K, (2) high root K uptake capacity, (3) early root vigour, high root-to-shoot ratios, and high root length densities, (4) proliferation of roots throughout the soil volume, and (5) high transpiration rates. Plant traits that increase KUtE include (1) effective K redistribution within the plant, (2) tolerance of low tissue K concentrations, and, at low tissue K concentrations, (3) maintenance of optimal K concentrations in metabolically active cellular compartments, (4) replacement of K in its non-specific roles, (5) redistribution of K from senescent to younger tissues, (6) maintenance of water relations, photosynthesis and canopy cover, and (7) a high harvest index. The development of crop genotypes with these traits will enable K fertiliser applications to be reduced.

Description: In S Spain, the Andalusian olive oil industry generates annually 2.5–3.0 million tons of olive mill pomace, a by-product which is comprised of the residues from the two-phase oil-extraction process. The agricultural policies of the EU have led to widespread interest in recycling these agricultural by-products. Olive mill pomace might be evaluated as an organic fertilizer after composting, however, before wider use of composted olive mill pomace is advocated, characterization of the final product is needed. In this study, the physico-chemical characteristics, net N mineralization, and the potential for N leaching of 7 out of the 11 olive-mill-pomace composts currently produced in the Andalusian olive mills were investigated. Compost of olive mill pomace differed in the proportions of raw materials co-composted with the olive mill pomace, such as olive leaf material, manure, and straw. In all the composts tested, organic matter, total C and K were high with 60.5%, 30.7%, and 1.7% on average, respectively, whereas total P was low (0.4%) and with intermediate levels of N (1.5%). Compost pH (8.03), electrical conductivity (2.85 dS m –1 ), and germination index (65% on average) were adequate for agricultural use. Furthermore, principal component analyses revealed a clear relationship between the quality of the composts and the proportion of manure mixed with the raw materials. Net N mineralization was negative on average (–20 μg IN g –1 ) after 1 y, but positive after 2 y of incubation with up to 94% of available N from the total N added and the short-term potential N leaching after compost application was negligible (less than 3.9% of added N) and much lower than the other N fertilizer with up to 80% added N leached. Overall, results of this study clearly show that these currently produced composts of olive mill pomace are suitable as soil improvers for agricultural purposes, but may not contribute significantly as a N fertilizer for up to 2 y after application.

Description: Potassium (K) availability in soils is largely governed by their mineralogical composition. The extent of weathering of primary K-bearing minerals, the chemical pathways through which weathering takes place, as well as the dynamic equilibrium between various K fractions in soils are factors which determine different soil types of varying K-supplying capacity. The marked variability of K availability in soils in South Asia needs to be taken into account when formulating K-management strategies in intensive cereal-based systems in response to K application. Evidence from long-term fertilizer experiments in rice–rice (R-R) or rice–wheat (R-W) systems strongly indicates significant yield responses to K application and negative K balances where K application is either omitted or applied suboptimally. However, K-fertilizer recommendations in South Asia are generalized over large areas while farmers neglect K application to crops and remove crop residues from fields. These practices may strongly affect yield and soil K-fertility status in the emerging rice–maize (R-M) systems in different locations of South Asia. The dry-matter yield of the R-M system is usually much higher than that of the R-R or R-W system causing high withdrawal of nutrients from the soil. The current review assesses various K forms and K availability in diverse soil types of South Asia supporting rice-based systems. Aspects considered include: long-term crop yield and its response to added nutrients, K balance for intensive rice-based systems, and the role of crop residues in supplying K to crops. Emerging data from either completed or on-going experiments on the R-M systems in India and Bangladesh have revealed very high system productivity and variable responses and agronomic K-use efficiency of maize and rice. Potassium responses of maize are extremely high and variable for soils in Bangladesh. Finally, a plant-based strategy for field-specific nutrient management is presented and the need for models and decision support systems for developing efficient K management of the R-M system is also discussed.

Description: Density fractionation along with ultrasonic dispersion is widely applied in soil science to obtain distinct fractions of soil organic matter. Density cut-off and dispersion energy are crucial parameters to yield fractions closely corresponding to their conceptual definitions. Our literature review revealed methodological discrepancies in the utilization of density-fractionation schemes. Strikingly, reasons for the selection of specific density or dispersion energy were rarely explained. Thus, it is not known how results of different approaches relate to each other. We therefore recommend testing and reporting effects of fractionation parameters on chemical and physical properties of fractions, to achieve agreement and coherence on parameters to be used and facilitate comparability in future studies.

Description: Acidification of animal slurry is recommended in order to reduce NH 3 emissions, but relatively little is known about the effect of such treatment on C and N dynamics during acidification, storage, and after soil application. A laboratory study was performed, and the CO 2 emissions from a high–dry matter slurry (HDM), a low–dry matter slurry (LDM), and the same respective acidified slurries (AHDM and ALDM) were followed during a storage period and after soil incorporation. The N-mineralization and nitrification processes, as well as microbial-biomass activity were also estimated in soil receiving both the acidified and nonacidified materials. We observed a strong CO 2 emission during the acidification process, and acidification led to a small increase in CO 2 emissions (≈ 11%) during storage of AHDM relative to HDM. No effect of LDM acidification on CO 2 emissions during storage was observed. About 30% of C released during storage of AHDM was inorganic C, and for ALDM the C release was exclusively inorganic. Soil application of AHDM and ALDM led to a decrease in soil respiration, nitrification, and microbial-biomass-C values, relative to soil application of HDM and LDM, respectively. Furthermore, it was shown that this effect was more pronounced in ALDM- than AHDM-treated soil. Considering both steps (storage and soil application), acidification led to a significant decrease of C losses and lower C losses were observed from LDM slurries than from HDM slurries.

Description: Kakamega district in Western Kenya represents the smallholder farming systems typical for much of the densely populated humid highlands in East Africa. A specific feature, however, is the presence of a protected forest reserve (Kakamega Forest National Park), covering some 20% of the district area. Year-round crop production with little use of external inputs is resulting in declining soil fertility and crop yields. Technologies to counteract fertility constraints are rarely implemented, as they do not consider system diversity or farm-specific characteristics. We surmised that farm type–specific targeting of technology options to address soil fertility–related production constraints would reduce the anthropogenic pressure on the resources of the adjacent Kakamega rainforest reserve. Based on Kenyan national census data, we selected 168 farms in physical proximity of the Kakamega forest and characterized them regarding production system and soil attributes. Cluster and principal component analyses identified five distinct farm categories. Three representative farms from each cluster group were subsequently selected to establish labor-use patterns, draw resource-flow maps, and determine NPK balances. Small subsistence-oriented farms were most common (〉 50%), with maize yields of 0.9 t ha –1 (Cluster 1). Most farmers relied on the forest to provide fire wood, animal feed, and medicinal plants. Mixed farms, combining subsistence maize with industrial crops, were differentiated by soil type, with tea being grown on Ferralsol (Cluster 3), and sugar cane being grown on Acrisol (cluster 4). The dependence on forest resources was limited to animal grazing and the collection of feed stuff (Cluster 3), or the extraction of medicinal plants (Cluster 4). Only few farms showed a high degree of market orientation of the food-crop production. These comprised either small farms with high investments in fertilizer and maize yields close to 2 t ha –1 (Cluster 2), or larger farms (1.6–3.9 ha) with low fertilizer but high hired-labor use (Cluster 5). Their reliance on forest resources was generally low. Resource flows showed mainly patterns of nutrient export in subsistence farms, and more complex flow patterns, involving several farm compartments, in the diversified farms. Partial nutrient balances were strongly negative for N and K, irrespective of soil or farm type. Soil-fertility characteristics reflected the nutrient balances with generally low C and N in all farms on Acrisol, and low P in farms not applying mineral fertilizers or farmyard manure. The proposed typology is expected to improve the targeting of technologies addressing soil fertility–related production constraints, and to reduce the pressure on forest resources. This is of particular importance in the case of small-scale subsistence and mixed farms close to the forest margin.

Description: Humic acids (HAs), similar to other fractions of humic substances (HSs), have a large number of reactive functional groups enabling them to aggregate in solutions. Regardless of the origin of humic acid (aqueous or soil), this aggregation process is dependent on environmental conditions and strongly influences the mobility of soluble ionic and molecular pollutants. The aim of this work was to monitor the aggregation process of two humic acids isolated from different mineral soils (IHSS Elliot soil HA standard and Rendzic Leptosol HA) in the 2–11 pH range. Changes in aggregate size in HA sols were followed up using dynamic light scattering (DLS), while zeta potential (ZP) measurements in the same pH range were performed applying laser Doppler electrophoresis (LDE) technique. The effect of HA sol concentration and soil source on aggregation was examined as well. Besides, HA samples were characterized using Fourier transform infrared (FT-IR) spectroscopy. By inspecting HA-particle-size dependence on pH, it can be concluded that both HAs in corresponding sols behave as molecular aggregates or supramolecular structures, formed from small individual moieties (sizes 〈 10 nm) at higher pH values. The ZP vs. pH curve for both HAs revealed the ZP minimum in the 5–7 pH range, caused most likely by dissociation of acidic functional groups prevailing at lower pH values and deaggregation predominating over dissociation at higher pH values.

Description: Research on how tillage-induced soil redistribution affects soil properties is limited for complex slopes in nonmechanized agricultural areas. The objectives of this study are (1) to examine the vertical redistribution of soil organic C (SOC), extractable P and K induced by tillage on a complex slope, (2) to assess the effects of tillage erosion on soil profile properties, and (3) to elucidate the variations in soil properties induced by both vertical mixture and downslope transport of soil within the landscape. Simulated tillage was conducted in the Yangtze Three Gorges Reservoir Area, China. The 137 Cs data showed that intense tillage caused the soil vertical mixture and downslope transport. The redistribution of 137 Cs and soil constituents varied with the number of tillage passes and location in relation to curvature. SOC was completely depleted with the disappearance of soil profiles at the summit position, while SOC concentrations decreased by 26% for the till layer and increased by 29% for the sublayer at the toeslope position for the 15-tillage operation, as compared with those of pretillage. The vertical redistribution of extractable P and K followed a similar pattern to that of SOC. The gap and variation in soil constituents between the till layer and sublayer declined after tillage, suggesting that the mixing effect of tillage attenuates the variability of soil properties in the vertical direction. Net loss and gain of soil constituents occurred at the summit and toeslope positions, respectively, suggesting that the downslope transport of soil induced by tillage accentuates the variability of soil properties in the lateral direction.

Description: The yield of rice ( Oryza sativa L.) has increased substantially with the development of new cultivars, but the role of potassium (K) requirement for the increase in grain yield and the genotypic advance is still unclear. In order to investigate this relationship a database of 1199 on-farm measurements (harvest index 0.4) comprising 〉 400 modern rice cultivars was collected during 2005–2010 across major irrigated lowland rice–production regions of China. This was used to evaluate the relationships among K requirement, grain yield, and genetic improvement. Across all the sites and seasons, mean reciprocal internal efficiency of K (RIE-K, kg K [t grain produced] –1 ) was 19.8 kg K (t grain) –1 and rice yield averaged 8.7 t ha –1 . Considering four levels of grain yield (〈 7.5, 7.5–9, 9–10.5, and 〉 10.5 t ha –1 ), the respective RIEs were 18.7, 19.4, 20.5, and 21.7 kg K (t grain) –1 . The gradual increase in the RIE-K with yield was attributed mainly to the increase in straw and grain K concentration and the decrease in the K harvest index. The RIE-K values for ordinary inbred, ordinary hybrid, and “super rice” were 18.5, 20.1, and 19.9 kg K (t grain) –1 , respectively. Examining the historical development of rice cultivars, the RIE-K decreased from 40.9 (Nanjing1, early tall, inbred) in the 1950s to 19.8 (IR24, semi-dwarf, ordinary inbred) in the 1970s, and then increased to 20.9 (Shanyou63, modern ordinary hybrid) in the 1980s and 20.6 kg K (t grain) –1 (II-you084, “super” rice) in the 2000s. This variation in RIE-K among grain-yield levels and cultivars highlights the importance of information on rice K requirement in calculating K balance and optimal K-fertilizer rate for rice production.

Description: It is essential to produce optimal crop yields while reducing adverse environmental impacts of overfertilization. Therefore, nutrient-efficient plants may play a major role in improving the efficiency of fertilizer use whilst increasing crop yields. This field trial was conducted to study the differences on absorption and utilization of nitrogen (N), phosphorus (P), and potassium (K) of K-efficient cotton genotype 103 and K-inefficient cotton ( Gossypium hirsutum L.) genotype 122 and their environmental and economic effects. The results show that seed cotton yield was significantly different between K-efficient cotton genotype 103 and K-inefficient cotton genotype 122; the yields of genotype 103 were 39.2%, 33.8%, and 25.0% higher than those of genotype 122 with no K fertilizer (K0), 112 kg K ha –1 K (K1), and 224 kg K ha –1 (K2), respectively. Even when no K fertilizer was applied, the yield of genotype 103 was still 7.9% higher than the yield of genotype 122 at the highest K level (K2). Further economic benefit analysis revealed that the value cost ratio (VCR) of genotype 103 was significantly higher than 122 at K0 and K1, and harvest index (HI) of genotype 103 was significantly higher than that of genotype 122 at all three K levels. In addition, when fertilized with K, partial factor productivity of applied K (PFP K ) of genotype 103 was dramatically higher than that of genotype 122, demonstrating that genotype 103 had stronger ability to utilize K. Besides, the N- and P-use efficiencies of genotype 103 were also higher than those of genotype 122. It is concluded that: (1) genotype 103 gives better profit than genotype 122 and (2) genotype 103 uses fertilizer more efficiently and reduced fertilizer inputs will alleviate environmental risks.

Description: The great achievement of the development of intensive in agriculture in China can be partly attributed to substantial increases in mineral-nutrient application. However, whereas farmers tend to apply high levels of nitrogen (N) and phosphorus (P) application of potassium (K) has been neglected. A greater understanding of the relationship between maize ( Zea mays L.) grain yield and K-application rate is thus required to provide an improved rationale for K fertilization for farmers in the various agro-ecological regions of China. In this study, a total of 2765 farmers' survey data and 3124 on-farm experiments across major maize agro-ecological regions in China were collected and evaluated for farmers' K-management status and to determine grain-yield response to K application. Nationally, the average K-application rate on farms was 26 kg K ha –1 and varied from 0 to 158 kg K ha –1 , with a coefficient of variation of 107%, but the applied K-fertilizer rates were not related to grain yield. Maize grain yields at recommended K rates increased by 14.0%, 14.7%, 19.4%, and 4.3% in Northeast China, North China Plain, Southwest China, and Northwest China, respectively, compared to zero K fertilization (K 0 ). Increased yield due to K fertilization (IY max , difference between maximum yield across all treatments and K 0 -treatment yield for each experiment) averaged 1.4 t ha –1 but varied widely in different agro-ecological regions. Soil extractable K (NH 4 OAc-K) and intercounty variation resulted in large variation in IY max in agro-ecological regions, as did other factors, such as use of particular maize hybrids, soil types, or years in different regions.

Description: Maintaining orchards with trees at optimal leaf nutrient concentrations is one of the key issues for maximizing yield. Experiments for evaluating and updating guidelines are very rare since they require several years of field experiments with mature fruit-bearing trees. In the present paper, we first evaluated the Israeli guidelines for citrus by comparing them to the Israeli orchard leaf mineral status using a 10-year leaf-mineral database (results of 20 244 leaf analyses from commercial orchards all over Israel). Then, we created an updated guideline using a second database (the Israeli National Wastewater Effluent Irrigation Surveys database; INWEIS). This database summarizes yield and leaf mineral concentrations of commercial orchards from all over Israel. The data were collected from 122 orchards: 39 orchards of “Oroblanco” Pomelit ( Citrus grandis ), 33 orchards of “Michal” mandarin ( C. reticulata ), 30 orchards of “Star Ruby” grapefruit ( C. paradise ), and 20 orchards of “Shamouti” oranges ( C. sinensis ) over a 7-year period. Based on the first database, there was a disagreement between recommendations and the leaf nutrient status ( e.g., the Israeli Ministry of Agriculture recommendations were higher than orchard median values), which indicated that the growers and/or the recommendations need to be corrected. Based on the INWEIS database, a new guideline was set. It was found that the optimal leaf nutrient concentrations for grapefruit trees are 1.7% to 2.1% dry weight (DW) for N, 0.08% to 0.010% DW for P, 0.37% to 0.48% DW for K, and 0.33% to 0.45% DW for Mg. For orange trees, the optimal leaf nutrient concentrations are 1.9% to 2.3% DW for N, 0.11% to 0.14% DW for P, 0.80% to 1.00% DW for K, and 0.19% to 0.26% DW for Mg. For mandarin trees, the optimal leaf nutrient concentrations are 2.0% to 2.4% DW for N, 0.09% to 0.12% DW for P, 0.55% to 0.69% DW for K, and 0.19% to 0.26% DW for Mg. Maintaining leaf nutrient concentrations within these ranges will support maximal yields of 110 to 120 t ha –1 for grapefruit, 65 to 70 t ha –1 for orange, and 60 to 70 t ha –1 for mandarin cultivars.

Description: About 7% of the total land around the globe is salt-affected causing a great loss to agriculture. Salt stress refers to the excessive amount of soluble salts in the root zone which induce osmotic stress and ion toxicity in the growing plant. Among toxic ions, sodium (Na + ) has the most adverse effects on plant growth by its detrimental influence on plant metabolism in inhibiting enzyme activities. An optimal potassium (K + ) : Na + ratio is vital to activate enzymatic reactions in the cytoplasm necessary for maintenance of plant growth and yield development. Although most soils have adequate amounts of K + , in many soils available K + has become insufficient because of large amounts of K + removal by high-yielding crops. This problem is exacerbated under sodic or saline-sodic soil conditions as a consequence of K + -Na + antagonism. Here K + uptake by plants is severely affected by the presence of Na + in the nutrient medium. Due to its similar physicochemical properties, Na + competes with K + in plant uptake specifically through high-affinity potassium transporters (HKTs) and nonselective cation channels (NSCCs). Membrane depolarization caused by Na + makes it difficult for K + to be taken up by K + inward-rectifying channels (KIRs) and increases K + leakage from the cell by activating potassium outward-rectifying channels (KORs). Minimizing Na + uptake and preventing K + losses from the cell may help to maintain a K + : Na + ratio optimum for plant metabolism in the cytoplasm under salt-stress conditions. It would seem a reasonable assumption therefore that an increase in the concentration of K + in salt-affected soils may support enhanced K + uptake and reduce Na + influx via HKTs and NCCSs. Although very useful information is available regarding K + -Na + homeostasis indicating their antagonistic effect in plants, current knowledge in applied research is still inadequate to recommend application of potassium fertilizers to alleviate Na + stress in plants under sodic and saline-sodic conditions. Nevertheless some encouraging results regarding alleviation of Na + stress by potassium fertilization provide the motivation for conducting further studies to improve our understanding and perspectives for potassium fertilization in sodic and saline-sodic environments.

Description: Silicon (Si), although not considered essential, has beneficial effects on plant growth which are mostly associated with the ability to accumulate amorphous (phytogenic) Si, e.g. , as phytoliths. Phytogenic Si is the most active Si pool in the soil–plant system because of its great surface-to-volume ratio, amorphous structure, and high water solubility. Despite the high abundance of Si in terrestrial biogeosystems and its importance, e.g. , for the global C cycle, little is known about Si fluxes between soil and plants and Si pools used by plants. This study aims at elucidating the contribution of various soil Si pools to Si uptake by wheat. As pH affects dissolution of Si pools and Si uptake by plants, the effect of pH (4.5 and 7) was evaluated. Wheat was grown on Si-free pellets mixed with one of the following Si pools: quartz sand (crystalline), anorthite powder (crystalline), or silica gel (amorphous). Silicon content was measured in aboveground biomass, roots, and soil solution 4 times in intervals of 7 d. At pH 4.5, plants grew best on anorthite, but pH did not significantly affect Si-uptake rates. Total Si contents in plant biomass were significantly higher in the silica-gel treatment compared to all other treatments, with up to 26 mg g –1 in aboveground biomass and up to 17 mg g –1 in roots. Thus, Si uptake depends on the conversion of Si into plant-available silicic acid. This conversion occurs too slowly for crystalline Si phases, therefore Si uptake from treatments with quartz sand and anorthite did not differ from the control. For plants grown on silica gel, real Si-uptake rates were higher than the theoretical value calculated based on water transpiration. This implies that Si uptake by wheat is driven not only by passive water flux but also by active transporters, depending on Si concentration in the aqueous phase, thus on type of Si pool. These results show that Si uptake by plants as well as plant growth are significantly affected by the type of Si pool and factors controlling its solubility.

Description: Before hydrochars can be applied as soil amendments in agriculture, information about how hydrochar application affects soil nutrient cycles and plant growth are necessary. In this study, incubation experiments were performed to investigate hydrochar effects on N concentrations (NO , NH ) in soils with different N pools (soil N, fertilizer N). A set of pot trials with three crop species (barley, phaseolus bean, leek) was conducted to determine hydrochar effects on plant N availability and biomass production after mineral-N fertilization. Results of the incubation experiments show that hydrochar reduced the concentration of mineral N in soil within the first week after incorporation, especially that of nitrate. This was particularly evident, when hydrochars with high C : N ratio, high DOC and low mineral-N contents were applied. Hydrochars promoted biomass production of barley and phaseolus bean in pot trials, which can be partly attributed to an increase in soil pH after hydrochar incorporation. Dry-matter yield of leek tended to decrease after hydrochar application. Hydrochars with high C : N ratio decreased the plant's N content, an effect that was strongest with increased hydrochar concentration. Hydrochars with low C : N ratio did not affect the crop's N uptake. Our results show that the use of hydrochars as amendment in arable field or horticultural pot production will require an adjustment of N-mineral-fertilization strategies.

Description: The aim of this review is to describe the main physicochemical characteristics of diverse types of humic-metal-phosphate acid complexes. The effects of these complexes on phosphorus (P) fixation in soils with different pH values and physicochemical features and on plant phosphorus uptake are also discussed. Humic-metal-phosphate complexes have apparent stability constants in the same range as those of metal-humic complexes, in solutions with diverse pH and ionic-strength values. Likewise, the molecular-size distribution of humic-metal-phosphate complexes as a function of pH is similar to that of potassium or sodium humates and metal-humic complexes. Humic-metal-phosphate complexes are able to decrease phosphate fixation in soils and increase plant growth and phosphate uptake. Phosphorus fertilizers containing humic-metal-phosphate complexes proved to be efficient to improve plant growth and P uptake with respect to conventional fertilizers such as single superphosphate. The values of parameters related to plant phosphorus-utilization efficiency (PUt E) suggest that the regulation of root acquisition of phosphate from these complexes could involve the interregulation of a system for the optimization of metabolic P utilization in the shoot and another system involving stress responses of roots under phosphorus deficiency.

Description: Hydrochars and biochars are products of the carbonization of biomass in different conversion processes. Both are considered suitable soil amendments, though they differ greatly in chemical and physical composition ( e.g., aromaticity, inner surface area) due to the different production processes (pyrolysis, hydrothermal carbonization), thus affecting their degradability in soil. Depending on the type, char application may provide soil microorganisms with more (hydrochars) or less (biochars) accessible C sources, thus resulting in the incorporation of nitrogen (N) into microbial biomass. A soil-incubation experiment was conducted for 8 weeks to determine the relationship between mineral-N concentration in the soil solution and microbial-biomass development as well as soil respiration. An arable topsoil was amended with two hydrochars from feedstocks with different total N contents. Biochars from the same feedstocks were used for comparison. Both char amendments significantly decreased mineral-N concentration and promoted microbial biomass compared to the nonamended control, but the effects were much stronger for hydrochar. Hydrochar application increased soil respiration significantly during the first week of incubation, simultaneous with the strongest decrease in mineral-N concentration in the soil and an increase in microbial biomass. The amount of N detected in the microbial biomass in the hydrochar treatments accounted for the mineral N “lost” from the soil during incubation. This shows that microbial immobilization is the main sink for decreasing mineral-N concentrations after hydrochar application. However, this does not apply to biochar, since the amount of N recovered in microorganisms was much lower than the decrease in soil mineral-N concentration. Our results demonstrate that while both chars are suitable soil amendments, their properties need to be considered to match the application purpose (C sequestration, organic fertilizer).

Description: Wheat ( Tritcum aestivum L.) genotypes were screened and characterized for performance under salt stress and/or water-logging. In a solution-culture study, ten wheat genotypes were tested under control, 200 mM–NaCl salt stress and 4-week water-logging (nonaerated solution stagnated with 0.1% agar), alone or in combination. Shoot and root growth of the wheat genotypes was reduced by salinity and salinity × water-logging, which was associated with increased leaf Na + and Cl – concentrations as well as decreased leaf K + concentration and K + : Na + ratio. The genotypes differed significantly for their growth and leaf ionic composition. The genotypes Aqaab and MH-97 were selected as salinity×water-logging-resistant and sensitive wheat genotypes, respectively, on the basis of their shoot fresh weights in the salinity × water-logging treatment relative to control. In a soil experiment, the effect of water-logging was tested for these two genotypes under nonsaline (EC = 2.6 dS m –1 ) and saline (EC = 15 dS m –1 ) soil conditions. The water-logging was imposed for a period of 21 d at various growth stages, i.e., tillering, stem elongation, booting, and grain filling alone or in combinations. The maximum reduction in grain yield was observed after water-logging at stem-elongation + grain-filling stages followed by water-logging at grain-filling stage, booting stage, and stem-elongation stage, respectively. Salinity intensified the effect of water-logging at all the growth stages. It is concluded that the existing genetic variation in wheat for salinity × water-logging resistance can be successfully explored using relative shoot fresh weight as a selection criterion in nonaerated 0.1% agar–containing nutrient solution and that irrigation in the field should be scheduled to avoid temporary water-logging at the sensitive stages of wheat growth.

Description: This study assessed the relationships between external K + supply and K + : Na + ratios associated with Na + toxicity in Jatropha curcas. Plants were exposed to increasing external K + concentrations (6.25, 12.5, 25, 37.5, and 50 mM), combined with 50 mM NaCl in a nutrient solution. Photosynthesis progressively increased as the external K + : Na + ratios increased up to 0.75. The increase of photosynthesis and plant dry matter correlated positively with K + : Na + in xylem and leaves. The transport rates of K + and Na + from roots to xylem and leaves were inversely correlated. These ions presented an antagonistic pattern of accumulation in all organs. Maximum rates of photosynthesis and plant growth occurred with leaf K + : Na + ratios that ranged from 1.0 to 2.0, indicating that this parameter in leaves might be a good indicator for a favorable K + homeostasis under salinity conditions. The higher K + affinity and selectivity compared with Na + in all organs associated with higher xylem flux and transport to shoots are essential for maintaining adequate K + : Na + ratios at the whole-plant level. These characteristics, combined with adequate K + concentrations, allow J. curcas to sustain high rates of photosynthesis and growth even under toxic NaCl levels.

Description: The impact of fertilization on maize ( Zea mays L.) yield and soil properties was investigated in a long-term (〉 18 y) experimental field in N China. A completely randomized block design with seven fertilizer treatments and four replications was used. The seven fertilizer treatments were (1) compost (COMP), (2) half compost plus half chemical fertilizer (COMP1/2), (3) balanced NPK fertilizer (NPK), (4–6) unbalanced chemical fertilizers without one of the major elements (NP, PK, and NK), and (7) an unamended control (CK). In addition to maize yield, soil chemical and biological properties were investigated. Compared to the balanced NPK treatment, maize yield from the COMP treatment was 7.9% higher, from the COMP1/2 was similar, but from the NP, PK, NK, and CK treatment were 12.4%, 59.9%, 78.6%, and 75.7% lower. Across the growing season, microbial biomass C and N contents, basal soil respiration, and fluorescein diacetate hydrolysis, dehydrogenase, urease, and invertase activities in the COMP and COMP1/2 treatments were 7%–203% higher than the NPK treatment. Values from all other treatments were up to 60% lower than the NPK treatment. Maize yield is closely related to the soil organic C (OC) and biological properties, and the OC is closely related to various biological properties, indicating that OC is a suitable indicator for soil quality. Our results suggest the most limiting nutrient for improving the yield or soil quality was P, followed by N and K, and balanced fertilization is important in maintaining high crop yield and soil quality. Additionally, increases in OC, N, and biological activities in COMP and COMP1/2 treatments imply that organic compost is superior to the chemical fertilizers tested.

Description: This greenhouse study tested the effect of smoke-water and the smoke-isolated biologically active compound karrikinolide (KAR 1 ) on growth and photosynthetic pigments of Jatropha curcas L. seedlings. Fifteen-day-old seedlings were sprayed once weekly for 5 weeks with three dilutions of smoke-water (1 : 250, 1 : 500, and 1 : 1000 v/v) or KAR 1 (10 –7 , 10 –8 , and 10 –9 M). Growth parameters and photosynthetic pigment concentrations of 75-d-old seedlings were measured. Foliar application of both smoke-water and KAR 1 on J. curcas seedlings showed significant increases in stem width, shoot length, chlorophyll a, chlorophyll b, total chlorophyll, and total carotenoid concentrations compared to the untreated control. KAR 1 significantly improved leaf area, shoot and root dry mass, seedling-vigor index, and photosynthetic pigments as compared to control treatments. These results suggest the possible use of smoke-water and KAR 1 to achieve a vigorous and well established crop of J. curcas.

Description: Adequate measurements of the nitrogen (N) concentration in the aboveground biomass of sugarcane throughout the growth cycle can be obtained using the critical N dilution curve (CNDC) concept, which provides an N-nutrition index (NNI). The aim of this work was to determine the CNDC value for Brazilian sugarcane variety SP81-3250, establish the critical concentration of N, and determine the NNI in the aboveground biomass throughout the cane plant and first ratoon crop cycles. The study was performed in three experimental areas located in São Paulo, Brazil, during the crop cycles of 2005/2006 (18-month cane plant) and 2006/2007 (first ratoon). The plant cane crop was fertilized with treatments of 40, 80, or 120 kg N ha –1 and a control treatment without N. After the plant cane harvest, rates of 0, 50, 100, or 150 kg N ha –1 were applied to the control plot and the 120 kg N ha –1 –treatment plot in a split-plot experimental design with four repetitions. Throughout both sugarcane cycles, measurements of aboveground biomass were used to determine the dry-mass (DM) production and N concentration for each treatment. CNDC varied between the growth cycles, with a higher N concentration observed in the initial stages of the first ratoon and a lower N dilution observed throughout the plant cane cycle. The NNI value indicated excessive N storage in the initial stages and limiting concentrations at the end of the growth cycle. CNDC and NNI allow for the identification of the N-nutrition variation rate and the period in which the nutrient concentration limits the production of aboveground biomass. The equations for the critical N (Ncr) level obtained in this study for plant cane (Ncr = 19.0 DM –0.369 ) and ratoons (Ncr = 20.3 DM –0.469 ) can potentially be used as N-nutritional diagnostic parameters for sugarcane N nutrition.

Description: The leaf nutrient concentrations and the N-to-nutrient ratios were analyzed to evaluate the nutritional status of holm oaks ( Quercus ilex L.) experiencing various anthropogenic pressures. Leaves (1 year old) of Q. ilex and surface soil (0–5 cm) surrounding the trees were collected at seven natural and seven urban sites in Campania Region (Southern Italy) and analyzed for the concentrations of macro (C, N, P, S) and micronutrients (Mn, K, Na, Cu, Mg, Ca, Fe, Zn). The available soil fraction of micronutrients was also evaluated. The nutrients showed different concentration ranges for the natural and the urban sites in the soil (total and available) and in the leaves, that we reported separately. Organic-matter content and macronutrient concentrations were higher in the natural soils, while the highest leaf N, S, and P concentrations were found at some urban sites. Concentrations of Cu, Na and Zn both in leaves and soil, and Mg and Fe in leaves from the urban sites appeared to be affected by air depositions. Manganese was the only micronutrient to show higher concentrations at the natural than at the urban sites, both in soil and leaves. For this nutrient, in addition, a relationship between leaf and available soil concentrations was found at the natural sites. The ratios between the concentrations of N and each studied nutrient in the leaves highlighted a different nutritional status between the plants from the natural and urban sites.

Description: Mixtures of peat and substrate clays are commonly used as growth media for horticultural plant production. A quality protocol for substrate clays defines a threshold value of active manganese (Mn act = sum of exchangeable and easily reducible Mn) in substrate clays of 〈 500 mg kg –1 to prevent toxic reactions of plants. This threshold value was tested in experiments with peat-clay blends under various growth conditions, and nutrient solution experiments were additionally conducted to investigate the effects of silicic acid and dissolved organic matter on the occurrence of Mn toxicity. Common bean ( Phaseolus vulgaris L.) and hydrangea ( Hydrangea macrophylla ) plants were cultivated in different peat-clay substrates and in peat under different moisture and pH levels. The clays varied in their Mn act content from 4–2354 mg kg –1 . The results of the substrate experiments reveal that a threshold value for Mn in substrate clays is not justified, as plants grown in all peat-clay substrates did not develop any Mn toxicity even at high substrate moisture or low pH conditions which are known to increase the Mn availability. The extraction of active Mn did not well reflect the Mn concentrations in plant dry matter and substrate solution. As plants tolerated high Mn concentrations in the substrate solution compared to the nutrient solution without toxicity symptoms, the influence of silicic acid and dissolved organic matter (DOM) on Mn toxicity was characterized in a nutrient-solution experiment. Manganese toxicity was clearly diminished by silicic acid application, but not by DOM. The former effect probably explains the tolerance of bean plants in peat substrates where high silicon concentrations in the substrate solution were observed. Peat-clay blends even provided up to five times more silicon to plants than pure peat.

Description: Silicon (Si) reduces arsenic (As) levels in rice shoot and grain. However, the underlying mechanisms remain unclear. In this study, we examined the effect of Si application to three rice paddy soils on the dynamics of Si, iron (Fe), phosphorus (P), and As in the soil solution, As accumulation in rice straw, flag leaf, husk, brown rice, and polished rice, and on As speciation in polished rice. Silicon application to soil increased the concentrations of Si, Fe, As, and P in the soil solution, while the redox potential was unaffected. Arsenic concentrations of straw, flag leaf, and husk were reduced by half by Si application, while As concentrations of brown and polished rice were decreased by 22%. The main As species in polished rice was arsenite, As(III), with a fraction of 70%, followed by dimethylarsinic acid (DMA) and arsenate, As(V), with 24% and 6%, respectively. Silicon application to the soil did not affect DMA or As(V) concentration of polished rice, while the As(III) concentration was reduced by 33%. These results confirm that Si reduces As(III) uptake and translocation into the shoot. Furthermore, data indicate that decrease of As concentration of polished rice is due to decreased As(III) transport into grain. Possible underlying mechanisms are discussed.

Description: Phosphorus (P) can be added to soil as inorganic P or crop-residue P, but little is known about how these two forms of P addition affect soil P pools and how their effect changes with the rate of P addition. A glasshouse experiment was conducted to assess the effect of inorganic P and P added as residues at different rates on (1) soil P pools at two time points: immediately after amendment and 42 d later, and (2) growth and P uptake by wheat at flowering (day 42). Three types of legume residues (faba bean young shoot, chickpea mature shoots with pods, and white lupin mature shoots without pods) were added to a loamy-sand soil at a rate of 5 or 15 g residue kg –1 . Inorganic P was added at four different rates (3, 10, 30, and 100 mg P kg –1 ) to give P-addition rates corresponding to the total P added with the different residues at the two residue rates. Soil P pool concentrations (microbial P, resin-P, NaHCO 3 -P, NaOH-P, HCl-P, and residual P) and wheat growth and P uptake (shoot and root) were measured after 6 weeks. Compared to inorganic P addition, P added with residues led to a 10%–80% greater increase in shoot biomass at the two highest P-addition rates. Wheat P uptake was positively correlated with resin-P and microbial-P concentrations in residue-P-amended soil, but with resin-P and NaOH-P i concentrations in soil amended with inorganic P. The concentration of HCl-P decreased by up to 30% from day 0 to day 42 in the residue treatments and that of residual P decreased by about 20% in all treatments during this period suggesting that these nonlabile P pools are quite dynamic and could serve as P source for plants.

Description: Jatropha curcas L. has recently attracted the attention of the international research community due to its potential as a biodiesel crop. In addition, its high resistance to drought and salinity is well known. Under arid and semiarid conditions, boron (B) concentrations in irrigation water can be higher than desired when water from industry, urban areas, or desalination is used. However, the growth and physiological responses of J. curcas plants to B excess in the irrigation water are unknown. Therefore, a greenhouse experiment was conducted to study the effects of B excess in the nutrient solution (0.25, 2, 4.5, and 7 mg L –1 B, applied as H 3 BO 3 ) on plant growth, mineral concentration in the different plant tissues, photosynthesis, water relations, chlorophyll fluorescence, chlorophyll concentration (as SPAD values), and composition of carbohydrates. Plant growth decreased with increasing B concentration in the nutrient solution; growth reduction was higher for roots than for leaves or stems. The B concentration increased in all plant tissues, in the following order: leaf 〉 root 〉 stem. These data indicate that the roots of J. curcas are more sensitive to B toxicity than the leaves and that B has restricted mobility inside these plants, accumulating mainly in the basal and middle leaves via the transpiration stream. Increasing B concentration in leaves decreased the A CO2 and the stomatal conductance, but the leaf water parameters were not affected. The data for chlorophyll concentration and chlorophyll fluorescence indicated that nonstomatal factors were involved in the A CO2 decline, whereas decreases in the parameters of PSII photochemistry due to B toxicity suggest that there was structural damage in chloroplasts. There was also a general tendency for a decrease in nonstructural carbohydrates in all plant tissues, possibly due to the decline in A CO2 . With excess B, the concentrations of K and Mg increased in leaves due to a decrease in the growth, while a typical antagonistic effect between B and P was evident from the P concentration decrease in leaves. In summary, J. curcas should be considered a B-sensitive plant, as a leaf B concentration of 1.2 mg (g dw) –1 caused a growth decline of approximately 30%.

Description: Different extraction methods are used world-wide in routine soil analysis to estimate long-term potassium (K) reserves for plants. In Sweden, K extracted with 2 M HCl at 100°C (K HCl ) is frequently used, although with limited understanding of the phases extracted. In the present study, we quantified the effects of this extraction on soil minerals in particle size fractions ranging from clay to sand, and estimated their relative contribution to K HCl . The study included three Swedish long-term agricultural field experiments with texture ranging from loamy sand to silty clay, as well as mineral specimens of K feldspar. Total weight loss of particle size fractions was determined, and quantitative and differential X-ray powder diffraction (QXRD, DXRD), applied on solids before and after extraction, was used to quantify the dissolution of individual mineral phases. QXRD and DXRD included spray-drying of samples, addition of an internal standard and full pattern fitting, where a combination of mineral-standard XRD traces was matched with the experimental one. Our results show that K HCl was primarily associated with clay minerals concentrated in the two finest fractions (2–20 and 〈 2 μm). Highly expandable and mixed-layer phyllosilicates were quantitatively the most important minerals dissolved. The K was released from micaceous layers in mixed-layer phyllosilicates with a vermiculitic character. Whether di- or trioctahedral, a shared property of the dissolved phases was that they were rich in Fe. In the loamy sand, the coarser fractions (20–2000 μm), where feldspars were prominent, accounted for 35% of K HCl . According to DXRD, there was no significant decrease in K feldspars in any of the samples, and K HCl data for the feldspar specimens suggest that clay minerals contributed at least 70% of K HCl also in the loamy sand. Our study provides insights about the soil minerals that contribute to the long-term K delivery capacity of soils and an explanation for the prior observation that K HCl is a dynamic fraction that can be affected by management.

Description: The supplies of water and nitrogen to a plant during its critical stages of growth are the main factors that define crop yield. A crop experiences irregular water deficits during its life cycle in rain-fed agriculture. An effective anti-stress-oriented approach therefore ought to focus on increasing the units of water productivity. The main objective of this conceptual review is to confirm that adequate K management can be used as an important tool to alleviate the negative effects of water deficit on plant growth, yield-component formation, and yield. The French and Schultz approach of using the water-limited yield (WLY) was modified in this review into a graphical form and was used to discriminate between yield fractions that depended on the volume of transpired water from those that were induced by K fertilizer. By using this method, it was possible to demonstrate the extent of several crop (winter wheat, spring triticale, maize, sugar beet) responses to the K supply. Yield increases resulting from K application mostly appeared under conditions of mild water deficit. As described for sugar beet, finding the critical period of crop K sensitivity is a decisive step in understanding its impact on water-use efficiency. It has been shown that an insufficient supply of K during crucial stages in the yield formation of cereals (wheat, spring triticale), maize, and sugar beet coincides with a depressed development in the yield components. The application of K fertilizer to plants is a simple agronomic practice used to increase crop tolerance to a temporary water shortage. It may be that the improvement of a plant's access to K during mild water-deficiency stress will increase water uptake by the root cells, which in turn increases their osmotic potential and thereby allows extension growth. This growth in turn promotes access to other mineral elements (including nitrogen) and water, which favor plant growth and yield.

Description: Our understanding of how mineral nutrition affects productivity and composition of bioenergy crops grown on marginal lands remains fragmented and incomplete despite world-wide interest in using herbaceous biomass as an energy feedstock. Our aim was to determine switchgrass ( Panicum virgatum L.) biomass production and maize ( Zea mays L.) grain yield on marginal soils used previously to evaluate the effect of soil phosphorus (P) and potassium (K) fertility on alfalfa ( Medicago sativa L.) forage production. Grain yield of maize was reduced on P- and/or K-limited plots that also impaired alfalfa forage yield, whereas switchgrass biomass yields were high even in plots possessing very low available P (4 mg kg –1 ) and K (〈 70 mg kg –1 ) levels. Linear-plateau regression models effectively described the relationship of soil test P and K to tissue P and K concentrations, and tissue P and K concentrations accurately predicted removal of P and K in harvest biomass. However, neither soil-test P and K, nor tissue P and K concentrations were effective as diagnostics for predicting switchgrass biomass yield nor could soil tests and their change with cropping predict nutrient removal. Concentrations of cellulose, hemicellulose, lignin, and ash were not influenced by P and K nutrition. Predicted bio-ethanol production was closely associated with biomass yield whereas high biomass K concentrations reduced estimated bio-oil production per hectare by as much as 50%. Additional research is needed to identify diagnostics and managements to meet the bioenergy production co-objectives of having high yield of biomass with very low mineral nutrient concentrations (especially K) while sustaining and improving the fertility of marginal soils.

Description: Optimal potassium (K) fertilization is beneficial for oilseed-rape ( Brassica napus L.) yield and quality. However, the discrepancy between the high K demand of winter oilseed rape and low soil fertility and insufficient potassium input has limited the sustainable development of oilseed-rape production. A series of on-farm experiments in the key winter oilseed-rape domains of China was conducted from 2004 to 2010 to evaluate K-fertilizer management for winter oilseed rape. Currently, the average NH 4 OAc-extractable K content in the 0–20 cm soil layer is 89.1 mg kg –1 indicative of “slight deficiency”. In addition, farmers in China usually fail to use sufficient K fertilizer in oilseed-rape production, the average mineral-potassium-fertilizer input in 2010 being only 35 kg K ha –1 , far lower than the recommended rate of potassium for winter oilseed rape. Adequate potassium fertilization significantly raises seed yield. The average yield-increase rate for the major production regions due to K-fertilizer application was 18.5%, and the average K fertilizer–use efficiency 36.1%. Based on the negative correlation between yield response to potassium fertilization and available soil K content, a soil-K-test index was established for winter oilseed rape with a threshold value for NH 4 OAc-extractable soil K of 135 mg kg –1 . When available soil K-content is below this threshold value, more K fertilizer should be applied to achieve high seed yield and to increase soil fertility. The major challenge for K-fertilizer management in winter oilseed-rape production in China will be to guide farmers in the different regions in making reasonable use of K fertilizer through soil K-testing technology in order to maintain both seed yield and soil fertility.

Description: Controlled-release urea (CRU) is a new type of urea, which may increase crop nitrogen (N)-use efficiency compared with conventional urea (CU), but the conditions where it outperforms urea are not well defined. A field experiment assessing responses of plant growth and grain yield of maize to CRU and irrigation was conducted on a typical agricultural farm in Shandong, China. Five treatments of the two types of urea (75, 150 kg N ha –1 , 0 kg N ha –1 ) were applied as basal fertilizer when sowing maize, and two water treatments (W 0 and W 1 ) were used 23 d after anthesis. Net photosynthetic rate ( P N ) and chlorophyll concentration as well as leaf-area index (LAI) increased significantly by both CRU and CU application, with the increases being larger in CRU-treated plants than in CU-treated plants at grain filling and maturing stages. CRU significantly enhanced the maximum photochemical efficiency ( F v  /  F m ), PSII coefficient of photochemical fluorescence quenching ( q P ), and actual quantum yield of PSII electron transformation (Φ PSII ) but decreased the nonphotochemical quenching (NPQ). Cob-leaf N concentration of CRU-treated plants was significantly higher than that of CU-treated plants under no irrigation, but not in the irrigation treatment 30 d after anthesis. Significant positive correlations were found between cob-leaf N concentration and P N both with and without irrigation. Grain yield of maize was significantly higher in the CRU treatment than in the CU treatment under both irrigation conditions. In conclusion, CRU as a basal application appeared to increase the N-use efficiency for maize relative to CU especially by maintaining N supply after anthesis.

Description: The objective of this study was to compare the residual effect of zinc (Zn) from three Zn chelates (Zn-aminelignosulfonate, Zn-AML; Zn-polyhydroxyphenylcarboxylate, Zn-PHP; and Zn-ethylenediaminedisuccinate, Zn-EDDS), applied at two rates (5 and 10 mg Zn [kg soil] –1 , respectively) to a previous crop, for a flax crop ( Linum usitatissimum L.). For the greenhouse experiment, two different soils were used: a weakly acidic soil, classified as Typic Haploxeralf (Soil acid ), and a calcareous soil, classified as Typic Calcixerept (Soil calc ). Plant availability of soil Zn was evaluated using the DTPA-triethanolamine (TEA), Mehlich 3, and low-molecular-weight organic acids (LMWOAs) methods. Easily leachable Zn was determined, and soil Zn status was characterized based on the Zn distribution in different fractions obtained by a sequential extraction. The Zn reserves after the previous crop were substantial and ranged from 2.85% to 5.61% of available Zn (Mehlich 3-extractable) with respect to the applied Zn. Plant parameters such as dry-matter yield, total Zn, and soluble Zn concentrations were measured, and Zn utilization by plants was calculated. In both soils, the highest concentrations of available Zn were associated with the application of Zn-AML at a rate of 10 mg Zn kg –1 . In Soil acid the largest quantity of easily leachable Zn was also observed with Zn-AML fertilizer. Similarly, Zn-AML resulted in the highest Zn concentration in flax seeds (229 mg Zn kg –1 and 72 mg Zn kg –1 for the highest rate of Zn application to Soil acid and Soil calc , respectively). The results suggest that these Zn chelates resulted in a residual effect in soils with appropriate concentrations of the most labile fractions of Zn and available Zn, particularly when Zn-AML was applied at the highest rate. This chelate was more effective in Soil acid than in Soil calc . In the weakly acidic soil at the lowest Zn level it was associated with the highest percentage of Zn utilization by the flax plant and the most effective Zn transfer from soil to the plant.

Description: Differences in the isotopic signature of organic matter between soil fractions are indicative of transformation and ageing processes. Here we show that with increasing microbial transformation measured by δ 15 N, there is a concomitant increase in carbon age as measured by 14 C. The age of the soil's heavy fraction further increases with microbial utilization, indicating that stabilized OM ages yet continues to be reused.

Description: Avoiding chemical and physical artifacts during sampling is crucial for realistic analyses of mineral and other colloids in soil. We developed a sampler, which allows for the in situ collection of Fe oxides that precipitate in their natural environment in a Bg horizon of a Calcaric Gleysol. Simultaneous measurements of redox-sensitive parameters confirmed temporal changes from Fe-reducing to Fe-oxidizing conditions on site.