ALBERT

Notes: Book reviewed in this article: SOILpak for Cotton Growers. Third edition 1998. Edited by David C. McKenzie.

Notes: Abstract. Preferential flow has been increasingly recognised as a major component of water movement in many soils, particularly clays. This paper reviews problems in the measurement of solute fluxes in these soils, and discusses the solutions that have been adopted in UK studies of cracking clay soils. The estimation of solute fluxes is subject to many sources of error, which are best reduced by replicated measurements, such as those available in multi-plot experiments.

Notes: Abstract. Soil cores from river marginal wetlands from three sites in the UK (Torridge and Severn catchments), sampled and restrained in PVC piping, were flooded with dilute aqueous potassium nitrate. Half of the cores were sterilized prior to flooding to destroy the denitrifying bacteria. The change in nitrate concentration in the flood-water was measured over time. It is argued that the observed nitrate depletion rates (from 1.2 to 4.7 kg ha−1 d−1) is the result of microbially-mediated denitrification. The results show the method to be a simple and direct procedure for the assessment of spatial variation in nitrate-sink capacity. The depth of the denitrifying layer at the soil–water interface was confirmed to be of the order of a few mm only. A one-dimensional model for the diffusive flux in the flooded soil was developed which, on differentiation, gave a predictive expression for denitrification rate in terms of the effective soil diffusion coefficient for nitrate, the flood-water depth and concentration, and the thickness of the microbially active zone.

Notes: Book reviewed in this article: The Soils and Land Use Potential of the Southern and Eastern Slopes of Kilimanjaro, Tanzania.

Notes: Abstract. A database of 1065 fields in all parts of Finland, two soil profiles (augerhole borings) per field, was screened for acid sulfate (a.s.) soils. Each field represented 2100 14;ha of cultivated land. Soil pH and redox potential were determined in the field, at intervals of 10 14;cm, to a depth of 200 14;cm. Of the maximum of 124 profiles considered as a.s. soils according to the Soil Taxonomy and ILRI (International Institute of Land Reclamation and Improvement) systems, 46 profiles exhibited pH 〈3.5. These represented 48 14;000 14;ha of land. More than half of these severely acidic soils were associated with reduced subsoils and probably contained actively oxidizing sulfidic materials within 150 14;cm of the soil surface, while the remaining profiles were oxidized at least down to 150 14;cm. Using Soil Taxonomy criteria, the total area of cultivated a.s. soils was 67 14;000–130 14;000 14;ha. The minimum estimates exclude soils that may be leached or too low in sulfide to meet the criteria of a.s. soils. Application of the ILRI system produced an estimate of 61 14;000–130 14;000 14;ha. In the maximum estimate, 27% of the profiles were raw, 61% ripe and 12% potential a.s. soils. According to the FAO/UNESCO system, the area of cultivated a.s. soils (pH 〈3.5 or assumed sulfidic materials) is considerably less: 43 14;000–78 14;000 14;ha. All these estimates are only a fraction of the area considered to be covered by a.s. soils by established Finnish criteria. The choice of estimate has important economic implications for liming subsidies and planning regulations for the drainage of a.s. soils.

Notes: Abstract. Crops grown on virgin upland Vertisols of Zambia, are reported to perform rather poorly. However, subsoiling followed by repeated cultivation over two years apparently improves crop growth. Highest yields were recorded under long-term cultivation (12 years). To evaluate the reasons for these differences in crop response to Vertisol management, physical and hydrodynamic characteristics of soil profiles were studied in three soil management systems. The management systems were: uncultivated or virgin land; land cultivated for two years; and land cultivated for 12 years. The mean soil aggregate size decreased with increased time of cultivation, mostly due to the decrease of the largest sized aggregates. The surface horizon dried more slowly on the long-term cultivation plot. A comparison of the hydraulic conductivities indicated that water intake in the deeper layers improved with increased period in cultivation. Oxygen diffusion measurements showed good aeration at field capacity, to a depth of 0.32m on the long-term cultivation plots, but only to 0.17 m and 0.25 m for 2 years cultivation and virgin plots respectively. Repeated cultivation was beneficial in improving surface soil tilth and in improving subsurface drainage, thus removing the problem of a perched water table which occurred close to the soil surface under natural conditions.

Notes: Abstract. The chemical extractability of heavy metals introduced into the soil during 7 years application of sewage sludge, composted municipal solid waste and sheep manure, and their availability to citrus plants were studied. The total content of metals in the soil (0-20 cm)was increased by the use of sludges and compost, but only the Ni content in the saturation extracts of soil was significantly increased. Total Cd, Cr, Cu, Ni, Pb, and Zn were sequentially fractionated into water-soluble plus exchangeable, organically bound, carbonate-associated, and residual fractions. Most of the heavy metals were present in carbonate and residual fractions, although substantial amounts of water-soluble plus exchangeable Cd, and organically bound Cu and Ni were found. No significant increases in the metal contents in leaves and orange fruits were observed, with the exception of Pb in leaves. Several statistically significant correlations between metal content in plants, metal content in soil fractions, and chemical characteristics of soil were also found.

Notes: Book reviewed in this article: Human impact on Erosion and Sedimentation By D. E. Walling & J.-L. Probst (editors).

Notes: Book reviewed in this article: Soil erosion by water in Africa: Principles, Prediction and Protection By D. Nill, U. Schwertmann, U. Sabel-Koscella, M. Bernhard & J. Breuer.

Notes: Abstract. To provide a practical aid to improving fertilizer practice a mechanistic model was developed that can be readily calibrated for widely different crops. Most of the inputs are easy to obtain and the others, the amounts of fixed soil-K and the velocity constants for fixation and release of soil-K, can be readily measured by a novel procedure which is described.The model calculates for each day the potential increase in plant weight and the increment in root length, from the current plant mass, its %K and pan evaporation. It calculates the maximum amount of K that could be transported through soil to the root surfaces. It modifies this potential uptake by taking account of the ‘feedback’ of plant K on root absorption to give the actual uptake and a new %K in the plant. It calculates the radii of the depletion zones around each root increment and the interchange between the solution, exchangeable and fixed-K in these zones and also in the undepleted regions of soil. Routines are included for the effects of weather on the various processes. Differences between species are accommodated by selecting one of three algorithms for root growth and by adjusting the values of two crop-K parameters that define the decline in a critical and a maximum possible %K with increase in plant mass per unit area.A simplified version of the model runs interactively on the Internet at:

Notes: Abstract. The effect of rate and timing of autumn/winter straw incorporation on the immobilization of spring-applied N-fertilizer are studied. The immobilization of 15N-labelled fertilizer by straw was determined in pot trials with a sandy loam soil (Wick series) collected from two field experiments. In experiment 1, straw was incorporated at four different rates in the autumn; experiment 2 had a fixed rate of straw (7.5 t/ha) incorporated at monthly intervals from September to March. Immobilization in spring was not enhanced when only stubble was incorporated in autumn. However, autumn incorporation of 7.5 t/ha straw resulted in a significant increase in the immobilization of spring-applied N, equivalent to 10 kg/ha; when 15 t/ha straw was incorporated, immobilization increased to 18 kg/ha. The enhancement of immobilization, immediately following fertilizer application, was dependent on the extent of straw decomposition prior to N application. Thus immobilization was related to cumulative thermal time (day °C above 0°C; Tsum between the date of straw incorporation and fertilizer application). Straw which had been incorporated for Tsum 〉 1200 no longer caused appreciable immobilization of spring fertilizer.

Notes: Book reviewed in this article: Erosion and sediment yield: global and regional perspectives Edited by D. E. Walling and B. W. Webb.

Notes: Abstract. The restorative ability of herbaceous (Psophocarpus palustris, Pueraria phaseoloides) and woody (Leucaena leucocephala, Senna siamea, Acacia leptocarpa, Acacia auriculiformis) legume species and of natural regrowth was studied on an eroded and compacted Oxic Paleustalf in southwestern Nigeria. Compared to the control treatment that was continuously cropped for 15 years, four years of fallowing significantly improved test crop yields. However, fallowing with the above species did not substantially improve soil properties, particularly soil bulk density. A longer fallow period may be needed to amend soil physical conditions of this degraded Alfisol. Soil chemical properties were greatly improved following land clearing and plant biomass burning in 1993. However, the residual effect of burning on soil fertility was insignificant in the second cropping year. Among the fallow species, P. palustris and natural fallow showed the best residual effect on test crop performance. Despite the high biomass and nutrient yields of S. siamea and A. auriculiformis, test crop yields on these plots were low due to the border effects from the uncleared and fallowed subplots.

Notes: Abstract. To study the influence of different vegetation species and plant properties on the generation of surface runoff and soil erosion in south east Spain, a series of rainfall simulation experiments was conducted on small (c. 1.5 m2) plots. These were carried out in October 1993 and May 1994 on two sites close to Murcia. Six vegetation types were studied, with some at different stages of maturity, giving a total of nine vegetation treatments and two bare soil treatments. Four replicates of each treatment were exposed to a rainstorm of 120 mm/h for 15 minutes. The results of the experiments show that there are few significant differences in the ability of the vegetation types studied to control runoff or soil erosion. Of the plant properties considered, only plant canopy cover showed a significant relationship with soil loss and runoff with the greatest reduction in soil loss taking place at canopy covers greater than 30%. The implications of this research are that future efforts should be directed at developing ecological successions and revegetation methods which promote a substantial and sustainable canopy cover.

Notes: Abstract. The effect of increasing rates of nitrogen (N) fertilizer on the yield response of 3 or 4 consecutive winter cereal crops after ploughing out grass was investigated at six field sites on commercial farms in England and Wales. Amounts of N required for an economically optimum yield (〉3 kg of grain for each kg of fertilizer N applied) ranged from 0 to 265 kg ha−1 and were dependent on soil N supply, but not on crop yield. Optimum N rates were large (mean 197 kg N ha−1) at three sites: two sites where cereals followed 2-year grass leys receiving low N inputs (〈200 kg N ha−1), and at one site where a cut and grazed 4-year ley had received c. 315 kg N ha−1 of fertilizer N annually. At the other three sites where 4 and 5-year grass leys had received large regular amounts of organic manures (20–30 t or m3 ha−1) plus fertilizer N (c. 300 kg ha−1 each year), optimum N rates were low (mean 93 kg N ha−1) and consistently over-estimated by the farmer by an average of 107 kg N ha−1. Optimum N rates generally increased in successive years after ploughing as the N supply from the soil declined. Determination of soil C:N ratio and mineral N (NO3N+NH4N) to 90 cm depth in autumn were helpful in assessing fertilizer N need. The results suggest there is scope to improve current fertilizer recommendations for cereals after grass by removing crop yield as a determinant and including an assessment of soil mineralizable N during the growing season.

Notes: Abstract. Soils, of clay texture, were taken from two crop rotations in a long term trial, (i) maize - spring oats - maize, (ii) maize - spring oats - autumn oats - red clover, and from an adjacent uncropped fenceline. Wet sieving was preceded by wetting under vacuum, wetting under tension or by direct immersion. The undisturbed soil was the most stable; the inclusion of clover in the rotation improved aggregate stability. Direct immersion was most disruptive in disintegrating aggregates followed by vacuum and pre-wetting under tension.

Notes: Abstract. A decision support system to predict the plant availability of nitrogen (N) following organic manure applications to land has been developed, drawing together the latest UK research information on factors affecting manure N availability and losses. The ADAS MANure Nitrogen Evaluation Routine (MANNER) accounts for manure N analysis, ammonia volatilization, nitrate leaching and mineralization of manure organic N. Only a few easily available inputs are required to predict the amount of N volatilized or leached, and the fertilizer N value for the next crop grown. Predictions from MANNER have been evaluated by comparison with independently collected data from a range of experimental studies where pig, cattle and poultry manures were applied to arable crops. Good agreement was found (r2 60–79%, P〈0.001), confirming that MANNER can provide a reliable estimate of the fertilizer N value of farm manures spread to arable land under a range of conditions.

Notes: Abstract. A lysimeter study from April 1993 to June 1997 assessed the effects of winter cover crops and unfertilized grass on both the volume of water draining over winter and the amounts of nitrate leached. There were three to five replicates of each treatment in a fully randomized design. The lysimeters were undisturbed monoliths of loamy medium sand, 1.2 m deep and 0.8 m diameter.There were six treatments: sown cover before spring-sown crops (SC), natural regeneration (‘tumbledown’) before spring-sown crops (T), unfertilized grass (UG), bare soil permanent fallow, (PF), winter barley (WB) and conventional overwinter fallow before spring-sown crops (WF). Sugarbeet replaced cereals in 1996 as a disease break, and in consequence no cover was established in SC and T in autumn 1996. Of the four years of the study, two were above-average rainfall, while two were of less than average rainfall. Results are only quoted if statistically significantly different from WB (P=0.10).Over the first winter, NO3―N losses were similar under UG (26 kg ha−1) and PF (29 kg ha−1), due to the slow establishment and growth of the grass. In the following three winters NO3―N losses under UG were small (c. 6 kg ha−1), giving an overall mean of c. 11 kg ha−1. Sown cover crops and T gave means of c. 16 and 22 kg ha−1 respectively, compared with c. 27–31 kg ha−1 under PF, WB and WF.Mean NO3―N concentrations were smallest under UG (4.4 mg l−1) and SC (10.6 mg l−1), although both T (13.7 mg l−1) and PF (12.4 mg l−1) were less than under WB and WF (15.8–18.7 mg l−1). Overwinter drainage was greatest from UG and PF, at 239 and 247 mm respectively. In the three winters that cover crops were grown, drainage was decreased by, on average, 30 mm year−1 compared with WF. However, there were large differences in effects between years, with significant decreases in only one year.We conclude that the widespread adoption of cover crops before spring-sown crops will reduce overwinter drainage in UK Nitrate Vulnerable Zones by no more than c. 2%, compared with no cover before spring-sown crops.

Notes: Abstract. Gross N mineralization and nitrification rates were measured in soils treated with dairy shed effluent (DSE) (i.e. effluent from the dairy milking shed, comprising dung, urine and water) or ammonium fertilizer (NH4Cl) under field conditions, by injecting 15N-solution into intact soil cores. The relationships between gross mineralization rate, microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) as affected by the application of DSE and NH4Cl were also determined. During the first 16 days, gross mineralization rate in the DSE treated soil (4.3–6.1 μg N g−1 soil day−1) were significantly (P 14;〈 14;0.05) higher than those in the NH4Cl treated soil (2.6–3.4 μg N g−1 soil day−1). The higher mineralization rate was probably due to the presence of readily mineralizable organic substrates in the DSE, accompanied by stimulated microbial and extracellular enzyme activities. The stable organic N compounds in the DSE were slow to mineralize and contributed little to the mineral N pool during the period of the experiment. Nitrification rates during the first 16 days were higher in the NH4Cl treated soil (1.7–1.2 μg N g−1 soil day−1) compared to the DSE treated soil (0.97–1.5 μg N g−1 soil day−1). Soil microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) increased after the application of the DSE due to the organic substrates and nutrients applied, but declined with time, probably because of the exhaustion of the readily available substrates. The NH4Cl application did not result in any significant increases in microbial biomass C, protease or urease activities due to the lack of carbonaceous materials in the ammonium fertilizer. However, it did increase microbial biomass N and deaminase activity. Significant positive correlations were found between gross N mineralization rate and soil microbial biomass, protease, deaminase and urease activities. Nitrification rate was significantly correlated to biomass N but not to the microbial biomass C or the enzyme activities. Stepwise regression analysis showed that the variations of gross N mineralization rate was best described by the microbial biomass C and N.

Notes: Abstract. The efficient use of biologically fixed N in agriculture is important in organic farming and when N fertilizers are either expensive or unavailable. The aim of the study was to determine the effects of cultivation and sowing dates on the efficiency of use of biologically fixed N built up during a period of grass/clover ley by subsequently sown ryegrass. Dates of cultivation in two field experiments conducted in consecutive years (1994/95 and 1995/96) ranged from August to October and sowing was carried out either immediately after cultivation or after a delay of one month. Nitrate-N losses through leaching, herbage yields and N offtake by ryegrass were measured from 1994 to 1996. A laboratory experiment was carried out to assess net N mineralization and nitrification in the soil of the field experiment under different conditions.The utilization of mineralized N ranged from 30 to 100 kg ha−1 in both field experiments. Herbage yield and recovery of mineralized N by ryegrass was greater when sowing was carried out immediately after cultivation than when it was delayed for one month. Cultivation in late October was inferior to cultivation in August or September but the optimum date (August to September) differed between the two years (1994/95 and 1995/96) due to differences in weather, especially rainfall, affecting N leaching during the germination and early growth phases. Indeed the main differences in the efficiency of utilization of mineralized N between treatments could be attributed to differences in NO3–N leaching losses during the autumn establishment period. Decreases in soil temperature during autumn resulted in a modest decrease in net N mineralization but a much more substantial decrease in the rate of nitrification, which has implications for NO3–N leaching. The optimum time for cultivation cannot be refined to a particular calendar date but reasonably accurate long-term rainfall forecasts in conjunction with data on soil moisture deficit would provide the means to set an optimum cultivation date.

Notes: Abstract. Deterministic leaching models are used to estimate regional losses of nitrate from agricultural land to the environment. The estimated leaching losses are associated with uncertainty arising from uncertainty in the input data used. In the present case study we have assessed this uncertainty by use of Monte Carlo analysis, using the Latin hypercube sampling technique. Input data have preferably been adopted from publicly available data. Data which could not be retrieved from the databases was assessed by guided estimates or based on local data. The estimated annual leaching loss from the study region was around 106 kg N ha−1, which is in agreement with previous findings. The uncertainty in the leaching expressed in terms of coefficients of variation (CV) depended on the agricultural practices. CV's for arable farm rotations, cattle farm rotations, and pig farm rotations were around 20, 30 and 40%, respectively. Breakdown of the total uncertainty into contributions of different error sources did not isolate one single all important source.

Notes: Abstract. The nitrogen (N) conserving effects of Italian ryegrass (Lolium multiflorum L.) undersown as a nitrate catch crop in spring barley (Hordeum vulgare L.) were evaluated over a ten-year period in outdoor lysimeters (1.5 m deep, diam. 1 m) with sandy loam soil. Spring barley grown every year received 11.0 or 16.5 g N m−2 before planting or was kept unfertilized. The N was given either as calcium ammonium nitrate or as ammoniacal N in pig slurry. From 1985 to 1989, ryegrass was undersown in the barley in half of the lysimeters while barley was grown alone in the remaining lysimeters. The grass sward was left uncut after barley harvest and incorporated in late winter/early spring. From 1990 to 1994 all lysimeters were in barley only.Barley dry matter yields and crop N offtakes were not affected by the presence of undersown ryegrass, although grain yields appeared to be slightly reduced. After termination of ryegrass growing, N offtake in barley (grain+straw) was higher in lysimeters in which catch crops had been grown previously.The loss of nitrate by leaching increased with N addition rate. Regardless of N dressing, ryegrass catch crops halved the total nitrate loss during 1985–1989, corresponding to a mean annual reduction in nitrate leaching of 2.0–3.5 g N m−2. From 1990 to 1994, lysimeters previously undersown with ryegrass lost more nitrate than lysimeters with no history of ryegrass. The extra loss of nitrate accounted for 30% of the N retained by ryegrass catch crops during 1985–1989.It is concluded that a substantial proportion of the N saved from leaching by ryegrass catch crops is readily mineralized and available for crop offtake as well as leaching as nitrate. To maximize benefits from ryegrass catch crops, the cropping system must be adjusted to exploit the extra N mineralization derived from the turnover of N incorporated in ryegrass biomass.

Notes: Abstract. Escherichia coli serotype O157 is a virulent human pathogen the global incidence of which has increased. It has been demonstrated that cattle are the primary reservoir of this pathogen. This has serious implications for the land-based disposal of organic wastes such as cattle manure, cattle slurry and abattoir waste. Further, it also has serious ramifications for the protection of surface and groundwater drinking supplies and public access to pasture land. However, while soil and vegetation can be expected to directly influence the survival of this pathogen, there is a paucity of information concerning the behaviour and survival of E. coli O157 in agricultural environments. It appears that E. coli O157 presently contaminates between 1 to 15% of UK cattle herds, depending on region, and that faecal excretion of the bacterium shows a distinct seasonality which also reflects the incidence of human infections. E. coli O157 can remain viable in soil for greater than 4 months and appears to be a highly resilient pathogen possessing the capability to adapt easily to environmental stresses. While most human cases of E. coli O157 related food poisoning have been associated with the consumption of contaminated meat and dairy products, there is also evidence that human infection has occurred through the ingestion of contaminated soil, fruit and vegetables and drinking water. In this review the potential threat to human health posed by the application of contaminated organic wastes to soil and possible strategies for reducing the amount of pathogen entering the food chain are highlighted.

Notes: Book reviewed in this article: Gaseous Nitrogen Emissions from Grasslands Edited by S.C. Jarvis & B.F. Pain.

Notes: Abstract. Growing cover crops during the winter before spring-planted crops is often suggested as an effective method to decrease nitrate leaching. A four-course crop rotation (potatoes-cereal-sugarbeet-cereal) was followed through two rotations on a sandy soil in the English Midlands. Three management systems were imposed on the rotation to test their effects on nitrate loss. The effects of cover crops on nitrate leaching and crop yields were compared with the more conventional practice of over-winter bare fallow before potatoes and sugarbeet.Cover crop N uptake was variable between years, averaging 25 kg ha−1, which is typical of their performance on sandy soils in the UK. The cover crops usually decreased nitrate leaching but their effectiveness depended on good establishment before the start of drainage. Over 7 years, cover crops decreased the average N concentration in the drainage from 24 to 11 mg l−1. Potato yield and tuber N offtake increased after cover crops. Ware tuber yield increased by an average of c. 8%; this was unlikely to be due to additional N mineralization from the cover crop because the potatoes received 220–250 kg fertilizer N ha−1, and non-N effects are therefore implicated. Sugar yield was not increased following a cover crop.After 8 years of nitrate-retentive practices, there were no measurable differences in soil organic matter. However, plots that had received only half of the N fertilizer each year contained, on average, 0.14% less organic matter at the end of the experiment.

Notes: Abstract. The effect of superficial liming of acidic forest soils on CO2 and N2O emissions and CH4 uptake was investigated with closed chambers in two deciduous and two spruce forests, by weekly to biweekly measurements over at least one year. The flux rates of untreated areas varied between 1.94 and 4.38 t CO2-C/ha per y, 0.28 and 2.15 kg/N2O-N/ha per y and between 0.15 and 1.06 kg CH4-C/ha per y. Liming had no clear effect on CO2 emissions which may change in the long-term with decreasing root turnover and increasing C-mineralization. Apart from one exception, liming resulted in a reduction of N2O emissions by 9 to 62% and in an increase of CH4 uptake by 26 to 580%. The variability in N2O emissions between the forest sites could not be explained. In contrast, the variability of annual CH4 uptake rates could be explained by N content (r2= 0.82), C content (r2= 0.77), bulk density (r2= 60), pore space (r2= 0.59) and pH (r2= 0.40) of mineral soil at a depth of 0 to 10 cm, and by the quantity of material in the organic layer (r2= 0.66). Experiments with undisturbed columns of the same soils showed that between 1 and 73% of the total N2O emissions came from the organic layer. However, atmospheric CH4 was not oxidized in this layer, which represents a diffusion barrier for atmospheric CH4. When this barrier was removed, CH4 uptake by the mineral soil increased by 25 to 171%. These results suggest that liming of acidic forest soils causes a reduction of the greenhouse gases N2O and CH4 in the atmosphere, due to changes in the chemical, biological, and physical condition of the soils.

Notes: Abstract. Agricultural soils, having been depleted of much of their native carbon stocks, have a significant CO2 sink capacity. Global estimates of this sink capacity are in the order of 20-30 Pg C over the next 50-100 years. Management practices to build up soil C must increase the input of organic matter to soil and/or decrease soil organic matter decomposition rates. The most appropriate management practices to increase soil C vary regionally, dependent on both environmental and socioeconomic factors.In temperate regions, key strategies involve increasing cropping frequency and reducing bare fallow, increasing the use of perennial forages (including N-fixing species) in crop rotations, retaining crop residues and reducing or eliminating tillage (i.e. no-till). In North America and Europe, conversion of marginal arable land to permanent perennial vegetation, to protect fragile soils and landscapes and/or reduce agricultural surpluses, provides additional opportunities for C sequestration.In the tropics, increasing C inputs to soil through improving the fertility and productivity of cropland and pastures is essential. In extensive systems with vegetated fallow periods (e.g. shifting cultivation), planted fallows and cover crops can increase C levels over the cropping cycle. Use of no-till, green manures and agroforestry are other beneficial practices. Overall, improving the productivity and sustainability of existing agricultural lands is crucial to help reduce the rate of new land clearing, from which large amounts of CO2 from biomass and soil are emitted to the atmosphere.Some regional analyses of soil C sequestration and sequestration potential have been performed, mainly for temperate industrialized countries. More are needed, especially for the tropics, to capture region-specific interactions between climate, soil and management resources that are lost in global level assessments.By itself, C sequestration in agricultural soils can make only modest contributions (e.g. 3-6% of total fossil C emissions) to mitigating greenhouse gas emissions. However, effective mitigation policies will not be based on any single ‘magic bullet’ solutions, but rather on many modest reductions which are economically efficient and which confer additional benefits to society. In this context, soil C sequestration is a significant mitigation option. Additional advantages of pursuing strategies to increase soil C are the added benefits of improved soil quality for improving agricultural productivity and sustainability.

Notes: Abstract. Field measurement of landfill methane (CH4) emissions indicates natural variability spanning more than seven orders of magnitude, from less than 0.0004 to more than 4000 g/m2 per day. This wide range reflects net emissions resulting from production (methanogenesis), consumption (methanotrophic oxidation), and gaseous transport processes. The determination of an ‘average’ emission rate for a given field site requires sampling designs and statistical techniques which consider spatial and temporal variability. Moreover, particularly at sites with pumped gas recovery systems, it is possible for methanotrophic microorganisms in aerated cover soils to oxidize all of the CH4 from landfill sources below and, additionally, to oxidize CH4 diffusing into cover soils from atmospheric sources above. In such cases, a reversed soil gas concentration gradient is observed in shallow cover soils, indicating bidirectional diffusional transport to the depth of optimum CH4 oxidation. Rates of landfill CH4 oxidation from field and laboratory incubation studies range up to 166 g/m2 per day, among the highest for any natural setting, providing an effective natural control on net emissions. It has been shown that methanotrophs in landfill soils can adapt rapidly to elevated CH4 concentrations with increased rates of CH4 oxidation related to depth of oxygen penetration, soil moisture, and the nutrient status of the soil.Estimates of worldwide landfill CH4 emissions to the atmosphere have ranged from 9 to 70 Tg/y, differing mainly in assumed CH4 yields from estimated quantities of landfilled refuse. At highly controlled landfill sites in developed countries, landfill CH4 is often collected via vertical wells or horizontal collectors. Recovery of landfill CH4 through engineered systems can provide both environmental and energy benefits by mitigating subsurface migration, reducing surface emissions, and providing an alternative energy resource for industrial boiler use, on-site electrical generation, or upgrading to a substitute natural gas. Manipulation of landfill cover soils to maximize their oxidation potential could provide a complementary strategy for controlling CH4 emissions, particularly at older sites where the CH4 concentration in landfill gas is too low for energy recovery or flaring. For the future, it is necessary to better quantify net emissions relative to rates of CH4 production, oxidation, and transport. Field measurements, manipulative studies, and model development are currently underway at various spatial scales in several countries

Notes: Book Reviewed in this article: Phosphorus loss from soil to water: Edited by H. Tunney, O. T. Carton, P. C.

Notes: Abstract. Variously timed sub-optimal irrigation strategies were applied to sugarbeet grown on a light soil (loamy sand or sandy loam) over four seasons (1991 to 1994) to investigate the effect on crop growth and nitrate leaching risk. Data from the two dry seasons, (1991 and 1994) are reported here. In the driest year (1991) soil mineral N levels after autumn harvest were negatively related to crop water use (P 〈 0.05). In this season, there was little drainage from the soil profile, and full irrigation reduced residual soil N by 31 kg N/ha (0-90 cm) compared with the unirrigated treatment (79 kg N/ha). The potential for N leaching during the ensuing winter was consequently more than halved. In 1991 and 1994 there was a strong positive linear relationship between dry matter yield, N uptake and water use, but a negative relationship between plant N concentration and water use. These relationships were a function of the severity and not the timing of drought. The additional N uptake associated with increased irrigation and crop water use was biased towards a large concentration in the aboveground crop (tops), which are normally returned to the soil. The C:N ratio of sugarbeet tops was affected by crop water supply with droughted crops having lower values. This would also influence N release and subsequent leaching risk. However, the effects of drought on N leaching risk were relatively small when compared with other root crops such as potatoes.

Notes: Abstract. The effects of tree crops on the soil physical properties of former agricultural land were compared with those of ley in a rotation with cereals on adjacent sites. Five sites in southern Sweden were investigated focussing on soil water retention characteristics, dry bulk density, macroporosity and saturated hydraulic conductivity. Three of the sites were on light textured soils and two on clay soils. The tree crops were 30 to 35-year-old hybrid aspen, Populus deltoides, and silver birch, Betula pendula, and the ley crops were one to five years old.The light-textured soils under tree crops showed bimodal pore size distributions in the macropore region, whereas under ley crops they showed unimodal distributions. Dry bulk densities were generally smaller and the macroporosities larger under tree crops compared with leyicereal crops. Saturated hydraulic conductivities tended to be larger under tree crops. Slopes of the linear regression lines between saturated hydraulic conductivity and each of the parameters dry bulk density, porosity and macroporosity were steeper in the soil under agricultural crops than under tree crops.Observed differences in physical properties were considered to be an effect of land use, which had brought about changes in aggregate stability, pore size distribution and pore continuity.

Notes: Abstract. Phosphorus concentrations and outputs have been compared and contrasted in six small agricultural catchments in the west and northeast of Scotland. The loss of P from soils to stream waters was more from catchments with intensive dairy cattle farming in the west than from the less intensively stocked/arable catchments in the northeast, with striking differences being seen between the two regions. In the northeast, intensive animal farming caused less P loss in drainage water than arable management.Larger mean annual concentrations were seen in the west (0.076-0.142 mg PO4-P/l as molybdate-reactive phosphate–MRP) compared with the northeast (0.012-0.025 mg PO4-P/l), a feature caused by the combination of limited P-retention in the western Gleysols and smaller inputs to the largely-podzolic northeastern catchments. Stream concentrations were decreased by dilution during winter storm flows and increased during summer baseflow and at the beginning of soil rewetting in autumn.

Notes: Book Reviewed in this article: Freshwater Contamination By B. Webb (editor).

Notes: Book Reviewed in this article: Biotechnical and soil bioengineering slope stabilization. A practical guide for erosion control By D. H. Gray & R. B. Sotir.

Notes: Abstract. This paper reports results from a four year study to investigate the suitability of porous ceramic cups to measure solute leaching on shallow chalk soils. Measurements were carried out in one field following surface applications of nitrate and bromide tracers and in two fields after only bromide was applied. Soil water samples were collected from porous cups at 30,60 and 90cm depth after every 25 mm of drainage, and soil samples from 0–30, 30–60 and 60–90 cm were collected monthly eachwinter. Soil matric suctions andvolumetric moisture content were measured in one winter. Leaching losses, measured with ceramic cups were compared with those measured by soil analysis. Porous cups installed in chalk at 60 and 90 cm depth were only able to collect samples regularly when soil matric suctions were less than 15 kPa. Water held at such low suctions is likely to move quickly through relatively large fissures in the chalk. The slow rate of equilibration between solute concentrations in water moving in macrofissures and those in water moving through micropores of the chalk matrix, means that porous cups may not provide good estimates of leaching losses if they are installed in chalk rock.

Notes: Abstract. Nitrate leaching after one year of a cut grass/clover ley was measured in two succeeding years to investigate how the postponing of ploughing leys from early to late autumn or spring, in combination with spring or winter cereals affected leaching of nitrate. The experiment was conducted as three field trials, two on a coarse sandy soil and one on a sandy loam soil. For calculation of nitrate leaching, soil water samples were taken using ceramic suction cups. The experiments started in spring in a first year ley and ended in spring three years later. Total nitrate leaching for the three year periods for each trial ranged between 160–254 and 189–254 kg N/ha on the coarse sand and 129–233 kg N/ha on the sandy loam. The results showed that winter wheat (Triticum aestivum L.) did not have the potential for taking up the mineralized N in autumn after early autumn ploughing of grass/clover leys, and that the least leaching was generally found when ploughing was postponed until spring, and when winter rye (Secale cereale L.) was grown as the second crop rather than spring barley (Hordeum vulgare L.). Nevertheless, leaching was generally high in the winter period even when winter rye was grown. On these soil types ploughing out should be postponed, whenever possible, to spring. Crop systems that maximize the utilization of mineralized N and thereby minimize nitrate leaching need to be further developed. Based on N balances, the data were further used to estimate the biological N fixation by the clover.

Notes: Abstract. Ceramic suction cups were used to obtain samples of soil solution from permanently grazed swards receiving 200 kg N/ha/y. The suction cups were installed in 1 ha plots at 10, 30 and 60 an depth in a poorly drained, heavy clay soil in S. W. England. The plots were hydrologically isolated from each other by perimeter drains which channelled surface runoff water into v-notch weirs. In one treatment, artificial drainage by a system of field and mole drains also converged to outfalls through v-notch weirs, which enabled samples to be taken. Nitrate and a range of other ionic constituents were examined over a 12 month period in soil solutions taken from the suction cups and compared with leachate obtained from the field drains and surface channels. Field drain samples frequently exceeded the EC limit of 11.3 mg nitrate-N/1, but concentrations in suction cups obtained during the same period did not, and were up to ten-fold less. Although correlations for ions were found between different sampling depths and drainage samples, no clear patterns emerged. It was concluded that suction cups were inappropriate for the determination of the overall leaching losses in this soil type, but provided useful data on changes in ionic concentrations which occurred in different soil horizons through to drainage outfalls.

Notes: Abstract. The impact of soil erosion on soil productivity was estimated for a Rhodic Ferralsol and a Eutric Cambisol in Santa Catarina, southern Brazil. Over equivalent periods, total soil losses were an order of magnitude different (868 and 68 t/ha respectively on the bare soil control), yet the impact on maize yield per tonne of soil lost was far greater at the Cambisol site with less erosion. Similar interesting contrasts between sites were found for the other measures of impact with decline in pH and phosphorus and increase in free aluminium being the most obvious induced soil differences. The results demonstrate the variable nature of erosion impact according to soil type and they highlight the importance of examining a number of measures of impact before pronouncing on the sustainability of any particular agricultural practice.

Notes: Abstract. Mubangwe Farm, northern Malawi, was brought into cultivation from savanna vegetation with Brachystegia between 1970 and 1983 to produce tobacco, maize and groundnuts. Because of poor yields even with inputs of lime, N, P and K the fields were soon abandoned. The soils were only moderately acidic with little likelihood of Al toxicity. They held only small amounts of exchangeable Ca2+ (down to 0.01 cmolc/kg) particularly at depth. Phosphorus availability was low particularly in the subsoil. A minus-one pot experiment showed that the growth of sorghum in topsoil samples was limited by lack of N, P, S and Ca. The lower availabilities of P and Ca in the subsoil are therefore likely to be major limitations to growth, allowing only limited root penetration. The loamy sand to sandy clay soils generally had small available water capacities (down to 0.07 cm3/cm3) which, with restricted root development, may have lead to drought in dry periods during the growing season. The findings emphasize the need to measure both subsoil and topsoil properties when new areas of land are being developed for crop production.

Notes: Abstract. Nitrogen (N) leaching losses from a shallow limestone soil growing a five course combinable croprotation (oilseed rape, wheat, peas, wheat, barley) were measured from 1990 until 1995 using porous ceramic cups, at 60 cm depth, and drainage estimates. The crops were grown with three husbandry systems and two levels of N fertilizer. The husbandry systems were designed to reflect local practice (Standard), the best possible techniques to reduce N loss (Protective) and an Intermediate system which was a compromise between the two. Nitrogen was applied at full and half recommended rates. Drainage started during September in four years and November in one year, with above average drainage in three years. Losses of N were largest after peas (58 kg/ha) and oilseed rape (42 kg/ha), and least (17 kg/ha) before peas sown in spring after a cover crop. Over five years, the Protective management system, which used early sowing and shallow cultivation wherever possible, lost least N (31 kg/ha/y) and the Standard system, with conventional drilling dates and ploughing as the primary cultivation, lost most (49 kg/ha/y). Halving the N fertilizer decreased N loss by 11 kg/ha/y, averaged over the rotation. None of the treatments gave mean drainage water nitrate concentrations of less than 50 mg/l, averaged over the five years. Changes to arable cropping alone will not eliminate the need for other measures to control nitrate concen-trations in public drinking water supplies.

Notes: Abstract. Soil salinity and alkalinity reduce plant production and alter species composition of meadow grasslands in western Jilin Province, China. This study was designed to compare the survival and growth of three grass species (Aneumlepidium chinense, Puccinellia tenuijlora and Hordeum brevisubulatum) transplanted into saline-alkali soils in the field, and to evaluate the effects of gypsum amendments on soil properties and growth of these species. Gypsum treatments decreased soil pH, electrical conductivity, and chloride and sodium levels; water infiltration and calcium levels were increased. Survival of grass transplants was increased by gypsum treatments. Tiller number and height, and grass yields were all increased by the application of gypsum. Improvements in plant growth and survival with gypsum treatment appeared to be due to reduced chloride levels and increased Ca availability in the soil, and to changes in soil structure leading to improved infiltration rates. Revegetation of salinelalkaline soils in this region would be improved by application of gypsum in the range of 14–19 t/ha.

Notes: Abstract. The Pilot Nitrate Sensitive Areas Scheme was set up in England in 1990 to test measures aimed at reducing nitrate losses from agricultural land. Ten groundwater catchments were chosen to typify the geology and farming of areas where nitrate concentrations in abstracted water were high. Voluntary and compensated controls on farming, based on recent research, were introduced. Scheme membership was for 5 years from 1990 or 1991, and 86% of the agricultural land entered the Scheme. On all farms entering the Scheme, manure and fertilizer use were restricted and green cover crops were required over winter (Basic Scheme). Additional payments were available for conversion of arable land to zero or low-input grassland (Premium Scheme). Intensive pig and poultry farmers were assisted with the costs of transporting manure for spreading over a wider area. The most effective changes were improved management of livestock manures, especially of the very large local quantities from housed pig or poultry units; conversion of arable land to low-input grassland; and use of cover crops. There were no indications of reduced crop yields but some requirements increased costs and management complexities. Estimates based on both model calculations and measurements indicated that nitrate losses from agricultural land decreased by about 30%, with considerable variation between areas.

Notes: Abstract. The structure of soils in areas of rain forest cleared for pasture is often compacted due to trampling by animals. When pasture is abandoned, regeneration of forest cover may be achieved from natural seed sources nearby.However, the regeneration of soil structure is also important for local hydrology and successful establishment of some plant species. In this study we investigated changes in soil structure and hydraulic properties in a series of plots on volcanic soils in the San Luis Valley, Costa Rica. The plots were current pasture, 15- and 20-year-old regenerating forest, and primary rain forest.Infiltration rate increased with increasing forest age and the water release characteristic reverted gradually from one with greater water retention at all matric potentials in the pasture plot towards that found in the primary forest. Compaction and low porosity were features of both the current pasture and 15-year-old regenerating forest in comparison to the primary forest.

Notes: Abstract. Over 170 countries have ratified the UN Framework Convention on Climate Change (UNFCCC) which aims at ‘the stabilisation of greenhouse gases in the atmosphere at a level that will prevent dangerous anthropogenic interference with the climate system’. The Kyoto Protocol, signed in 1997, commits the developed (‘Annex 1′) countries to a reduction in gaseous emissions. The global increase in atmospheric CO2, the main greenhouse gas, comes mainly from fossil fuels (6.5 Gt C yr−1), together with about 1.6 Gt C yr−1 from deforestation. The atmospheric increase is only 3.4 Gt C yr−1, however, due to a net sink in terrestrial ecosystems of about 2 Gt C yr−1, and another in the oceans. Increasing net carbon sequestration by afforestation of previously non-forested land is one way of reducing net national emissions of CO2 that is permitted under the Kyoto Protocol. Future modifications may also allow the inclusion of carbon sequestration brought about by other forestry and agricultural land management practices. However, associated changes in net fluxes of two other greenhouse gases identified in the Protocol — nitrous oxide (N2O) and methane (CH4) — will have to be taken into account. Growth of biomass crops can increase N2O emissions, and drainage of wetlands for forestry or agriculture also increases them, as well as emissions of CO2, while decreasing those of CH4. The problems of how to quantify these soil sources and sinks, to maximize soil C sequestration, and to minimize soil emissions of CH4 and N2O, will present a major scientific challenge over the next few years — one in which the soil science community will have a significant part to play.

Notes: Abstract. The effectiveness of Festuca ovina and Poa pratensis as contour grass strips for erosion control was examined in a laboratory experiment for an crodible sandy loam soil on 21, 25 and 29% slopes. No significant differences P〈0.05 were observed in runoff between the plots with grass strips and bare soil but significant differences in soil loss were recorded. Both grasses reduced crosion in the early part of the simulated storms by ponding water behind the barrier, filtering sediment and causing deposition within the ponded area. The P. pratensis barrier was less rigid and became flattened under submergence in the later part of the storms. Runoff flowed over the grass strip forming rills on the slope below, which then cut back and undermined the barrier. These barriers resulted in as much soil loss as bare soil towards the end of the storms on all three slopes. The F. ovina was effective in controlling erosion on the 21% and 25% slopes but not on the 29% slope.

Notes: Abstract. The recommended method of reducing the emission of NH3 while spreading manure is to plough or harrow the manure into the soil. This in turn increases the possibility of N2O emission. At two sites in southern Sweden emissions of NH3 and N2O were measured after spreading pig slurry by broadcasting and band spreading. The band spreading technique can be used in growing crops i.e. when nitrogen is most needed, and it is thought that the NH3 emission is smaller with this technique compared to broadcasting. The average NH3 loss was 50% of applied NH4+ during warm/dry conditions and 10% during cold/wet conditions. The N2O emission was always less than 1% of applied NH4+. When the NH3 emission decreased, the direct N2O emission increased. However, when taking into account the indirect N2O emission due to deposition of NH3 outside the field, the spreading techniques all produced similar total N2O emissions. The ammonia emission was not much lower for the band spreading technique compared to broadcasting, when compared on seven occasions.

Notes: Book reviewed in this article: Soil Erosion at Multiple Scales: Principles and Methods for Assessing Causes and Impacts Edited by F. W. T. Penning de Yries, F. Agus & J. Kerr

Notes: Abstract. Methane (CH4) is an important greenhouse gas. Flooded rice fields (paddies) are a significant source of atmospheric CH4; estimates of the annual emission from paddies range from less than 20 to 100 million Tg, with best estimates of 50 × 20 Tg. The emission is the net result of opposing bacterial processes: production in anaerobic microenvironments, and consumption and oxidation in aerobic microenvironments, both of which occur sequentially and concurrently in flooded rice soils. With current technologies, CH4 emission from rice fields will increase as production increases. Over the next 25 years rice production will have to increase by 65% from the present 460 Mt/y to 760 Mt/y in 2020. The current understanding of the processes controlling CH4 fluxes, rice growth and rice production is sufficient to develop mitigation technologies. Promising candidates are changes in water management, rice cultivars, fertilization, and cultural practices. A significant reduction of CH4 emission from rice fields, at the same time that rice production and productivity increase at the farm level, is feasible, although the regions where particular practices can be applied, and the trade-offs that are possible, have still to be identified.

Notes: Abstract. Increases in the emissions of globally important nitrogen (N) oxide gases have coincided with significant changes in land use in the tropics. Clearing of tropical forests and savannas for agriculture currently represents the most extensive alteration of land cover on the planet. Over the last several decades, N fertilizer use has increased globally, and in China and the developing world, use has recently surpassed that in the developed world. The potential contribution of land-use change in the tropics to the increase in N oxides is great, yet only a few studies have measured N oxide emissions after tropical land conversion. Our summary of available research shows some conversions to pastures and a few management practices, especially those using N fertilizers, increase emissions beyond those found in undisturbed ecosystems. However, not all studies show unequivocal increases in emissions. Accordingly, we call for a mechanistic understanding of the processes controlling trace gas fluxes to adequately predict under what conditions increased emissions may occur. More measurements are needed to build and test models that may improve management of N fertilizer use in tropical agricultural systems. Given the expected expansion of agriculture and increased use of N fertilizers in the tropics, increased emissions of N oxides from the tropics are likely.

Notes: Abstract. Grazing animals on managed pastures and rangelands have been identified recently as significant contributors to the global N2O budget. This paper summarizes relevant literature data on N2O emissions from dung, urine and grazed grassland, and provides an estimate of the contribution of grazing animals to the global N2O budget.The effects of grazing animals on N2O emission are brought about by the concentration of herbage N in urine and dung patches, and by the compaction of the soil due to treading and trampling. The limited amount of experimental data indicates that 0.1 to 0.7% of the N in dung and 0.1 to 3.8% of the N in urine is emitted to the atmosphere as N2O. There are no pertinent data about the effects of compaction by treading cattle on N2O emission yet. Integral effects of grazing animals have been obtained by comparing grazed pastures with mown-only grassland. Grazing derived emissions, expressed as per cent of the amount of N excreted by grazing animals in dung and urine, range from 0.2 to 9.9%, with an overall mean of 2%. Using this emission factor and data statistics from FAO for numbers of animals, the global contribution of grazing animals was estimated at 1.55 Tg N2O-N per year. This is slightly more than 10% of the global budget.

Notes: Abstract. Increases in the atmospheric concentrations of nitrous oxide (N2O) contribute to global warming and to ozone depletion in the stratosphere. Nitric oxide (NO) is a cause of acid rain and tropospheric ozone. The use of N fertilizers in agriculture has direct and indirect effects on the emissions of both these gases, which are the result of microbial nitrification and denitrification in the soil, and which are controlled principally by soil water and mineral N contents, temperature and labile organic matter.The global emission of N2O from cultivated land is now estimated at 3.5 TgN annually, of which 1.5 Tg has been directly attributed to synthetic N fertilizers, out of a total quantity applied in 1990 of about 77Tg N. This amount was 150% above the 1970 figure. The total fertilizer-induced emissions of NO are somewhere in the range 0.5-5 Tg N. Mineral N fertilizers can also be indirect as well as direct sources of N2O and NO emissions, via deposition of volatilized NH3 on natural ecosystems and denitrification of leached nitrate in subsoils, waters and sediments.IPCC currently assume an N2O emission factor of 1.25 ± 1.0% of fertilizer N applied. No allowance is made for different fertilizer types, on the basis that soil management and cropping systems, and unpredictable rainfall inputs, are more important variables. However, recent results show substantial reductions in emissions from grassland by matching fertilizer type to environmental conditions, and in arable systems by using controlled release fertilizers and nitrification inhibitors. Also, better timing and placement of N, application of the minimum amount of N to achieve satisfactory yield, and optimization of soil physical conditions, particularly avoidance of excessive wetness and compaction, would be expected to reduce the average emission factor for N2O. Some of these adjustments would also reduce NO emissions. However, increasing global fertilizer use is likely to cause an upward trend in total emissions even if these mitigating practices become widely adopted.

Notes: Abstract. The validity of the model described in Greenwood & Karpinets (1997) was tested against the results of single year, multi level K fertilizer experiments. Measurements of plant mass, %K in the plant and K activity ratio in soil had been made at harvest and at intervals during the growing season on spring wheat, summer cabbage and turnips. Reasonably good agreement was obtained between these measurements and simulated values when the two ‘crop’ parameters (defining the dependence of critical and maximum possible %K on plant mass) were adjusted for each crop. Also good agreement was generally obtained for plant weight and plant %K at harvest in less detailed experiments on 10 other crops. Values of the two ‘crop’ parameters for 12 of the crops were strongly correlated with one another suggesting that a single ‘crop’ parameter may be all that is required to define most inter-species differences in plant-K demand.Simulations with the model indicate that, in central England, no response of 10 crops to K fertilizer would be likely on soils containing more than 170 mg of 1 M ammonium nitrate extractable-K/kg of soil and having clay contents of between 15 and 45%. Shortcomings of the model and opportunities for advance are discussed.A simplified version of the model runs on the Internet at:

Notes: Abstract. As part of a study of recession farming on the ‘fadama’ lands on a segment of the Komadugu-Yobe floodplain, a survey was carried out to investigate the local farmers’ perception of soil types and management practices. The farmers are clearly aware of the differences in soil type on the fadama and they possess unique skills in managing their farm lands. The farmers classify fadama soils for recession farming by assessing soil texture and soil drainage conditions by feel and observation. Integrating such local knowledge into soil surveys will lead to better practical definition of mapping units and give soil names that have more meaning for the farmers.

Notes: Abstract. The large boreal peatland ecosystems sequester carbon and nitrogen from the atmosphere due to a low oxygen pressure in waterlogged peat. Consequently they are sinks for CO2 and strong emitters of CH4. Drainage and cultivation of peatlands allows oxygen to enter the soil, which initiates decomposition of the stored organic material, and in turn CO2 and N2O emissions increase while CH4 emissions decrease. Compared to undrained peat, draining of organic soils for agricultural purposes increases the emissions of greenhouse gases (CO2, CH4, and N2O) by roughly 1t CO2 equivalents/ha per year. Although farmed organic soils in most European countries represent a minor part of the total agricultural area, these soils contribute significantly to national greenhouse gas budgets. Consequently, farmed organic soils are potential targets for policy makers in search of socially acceptable and economically cost-efficient measures to mitigate climate gas emissions from agriculture. Despite a scarcity of knowledge about greenhouse gas emissions from these soils, this paper addresses the emissions and possible control of the three greenhouse gases by different managements of organic soils. More precise information is needed regarding the present trace gas fluxes from these soils, as well as predictions of future emissions under alternative management regimes, before any definite policies can be devised.

Notes: Abstract. The projected increase in sewage sludge used on land within many countries in the European Community will provide a major source of entry for several heavy metals into the soil. Although the application rate of sewage sludge to agricultural land is constrained by maximum annual additions of heavy metals, there is a need to know the sensitivity of those soils to heavy metal inputs which are physically suited for application. A rulebased classification using weighted parameters designed to assess the metal binding capacity of soil and the risk of groundwater pollution has been applied to soils data held within the Macaulay Land Use Research Institute's National Soils Inventory The classification uses soil pH, organic matter content, texture and soil colour as a surrogate for iron oxide concentration. The results indicate that some metals, for example cadmium and zinc are potentially more mobile in soils than others such as lead, but that the majority of soils display a strong or very strong binding capacity for all the metals. However this pattern can only be sustained if the soil pH values are maintained at their present values; a fall of one pH unit marks a dramatic shift towards the weak and moderate binding classes. The approach is largely unvalidated but does provide a useful framework for incorporating our mechanistic understanding of processes into wide area soil quality assessments and in identifying future research opportunities.

Notes: Abstract. Kriging is used to provide detailed quantitative information for a range of soil characteristics across the floodplain of the River Gambia. Application of spatial statistics to a large area with a coarse grid of data points produces spurious patterns unless the area is first partitioned into soil-geomorphic mapping units, each of which has a unique pattern of spatial variation. Even combining classical soil survey method with spatial statistics, the large short-range variability of acid sulphate soils means that single factor maps conceal a large element of uncertainty. A more robust procedure is to map the probability of occurrence of critical values of key characteristics.

Notes: Abstract. Field experiments undertaken at 14 sites, on a range of soil types, in lowland England, during the cropping years 1989–1993, tested the effectiveness of cattle or pig slurry as a source of nitrogen for cereal cropping. Slurry was applied in autumn, winter and spring, to autumn and spring sown cereal crops. Assessments included slurry nitrogen efficiency relative to N in spring applied fertilizer in terms of both grain yield and grain protein production, apparent crop recovery and content of mineral nitrogen in soil profiles. Crop response to nitrogen was poor at seven sites where high residues of soil mineral nitrogen (SMN) were present. On the seven responsive sites, spring slurry applications proved more efficient (mean 40%) as a source of N than autumn (mean 24%) or winter applications (mean 32%). These differences were smaller than reported in a number of other studies, probably as a result of relatively low excess winter rainfall, resulting in less nitrate leaching during the period of the investigation. Rapid incorporation into the topsoil of slurry applied in autumn, increased (28 kgN/ha) the SMN of samples taken early in the winter. However this increase did not lead to a consistent improvement in crop N uptake. Slurry dressings, whenever applied, can be expected to make a significant contribution to the N requirement of the succeeding crop and need to be taken into account when calculating the appropriate spring fertilizer application.

Notes: Abstract. Soils in areas with high livestock density contribute to the eutrophication of aquatic ecosystems through loss of nutrients, especially phosphorus (P). In order to identify the potential for P loss from such soils we determined phosphorus extracted by water (H2O-P), by double lactate (DL-P), and P sorption capacity (PSC) and degree of P saturation (DPS) in soil samples from two counties, one with low (Harle-catchment) and the other with very high livestock density (Vechta). Both catchments are hydrologically connected with the tidal areas of the North Sea.The mean concentrations of H2O-P (0.4mmol/kg) and DL-P (3.9 mmol/kg) were lower in the Harle-catchment than in the Vechta area (1.2 mmol/kg, 6.8mmol/kg). Although oxalate-extractable Al (Alox) and Fe (Feox) and the derived PSCs varied according to soil type and to land use, the livestock density and the resulting high concentrations of oxalate-extractable P (Pox) were shown to be the main reason for the very high DPS of up to 179% in the county of Vechta. These values exceeded DPS reported from other intensive pig feeding areas in western Europe and indicate the potential for significant P loss. Less than 40% of the variation in Pox could be explained by the routinely determined H2O-Por DL-P. Geostatistical analyses indicated that the spatial variability of Pox depended on manurial history of fields and Alox, showed still smaller-scale variability. These were the major constraints for regional assessments of P losses and eutrophication risk from agricultural soils using available soil P-test values, digital maps and geostatistical methods.

Notes: Abstract. Although gypsiferous soils cover approximately 100 million ha in the world, it is only in the past two decades that their pedogenic and agronomic properties have been better understood and their classification improved. There is still no method to assess adequately their production potential.This paper focuses on gypsum accumulation forms as diagnostic criteria for a rapid soil suitability appraisal in the field. Pseudomycelia, gypsum spots, powdery coatings and other localized in situ precipitations usually indicate soils with less than 15% gypsum. Depending on their intensity and depth of occurrence in the root zone, they define a soil environment which is suitable for semi-sensitive and semi-tolerant crops. Continuous gypsum accumulations characterize soils or horizons with high (e.g. more than 25%) gypsum contents, and these can be used only for tolerant crops.The land use potential of gypsiferous soils is primarily determined by: (a) the depth of the impermeable layer, (b)the gypsum content within the root zone, and (c) the crop tolerance level. A method is proposed to assess the land suitability of gypsiferous soils on the basis of these criteria.

Notes: A standardized dataset of derived soil properties for the 106 soil units considered on FAO-UNESCO's 1:5 million scale Soil Map of the World is presented. It was derived from a statistical analysis of the 4353 soil profiles held in the WISE (World Inventory of Soil Emission) database, which was developed at the International Soil Reference and Information Centre (ISRIC) for the geographic quantification of soil factors that control processes of global change. Median values are presented by soil unit for selected soil properties including: pH(H2O); organic carbon content; cation exchange capacity; sum of exchangeable Ca2+, Mg2+ and K+; exchangeable sodium percentage; bulk density; total porosity; available water capacity; soil drainage class; and gravel content class. Medians for these variables are presented both for the topsoil (0–30 cm) and subsoil (30–100 cm), where applicable. The data set can help to refine ratings for soil quality in global environmental models pending the availability of comprehensive georeferenced databases on soil and terrain resources such as SOTER, the World Soil and Terrain Database. In a Geographical Information System (GIS) it can be linked to the units shown on the digital Soil Map of the World through the legend code.

Notes: Abstract. The effect of grazing pressure on infiltration, runoff, and soil loss was studied on a natural pasture during the rainy season of 1995 in the Ethiopian highlands. The study was conducted at two sites with 0–4% and 4–8% slopes at the International Livestock Research Institute (ILRI) Debre Zeit research station, 50 km south of Addis Ababa. The grazing regimes were: light grazing stocked at 0.6 animal-unit-months (AUM)/ha; moderate grazing stocked at 1.8 AUM/ha; heavy grazing stocked at 3.0 AUM/ha; very heavy grazing stocked at 4.2 AUM/ha; very heavy grazing on ploughed soil stocked at 4.2 AUM/ha; and a control with no grazing. Heavy to very heavy grazing pressure significantly reduced biomass amounts, ground vegetative cover, increased surface runoff and soil loss, and reduced infiltrability of the soil. Reduction in infiltration rates was greater on soils which had been ploughed and exposed to very heavy trampling. It was observed that, for the same % vegetative cover, more soil loss occurred from plots on steep than gentle slopes, and that gentle slopes could withstand more grazing pressure without seriously affecting the ground biomass regeneration compared to steeper slopes. Thus, there is a need for developing ‘slope-specific’ grazing management schedules particularly in the highland ecozones rather than making blanket recommendations for all slopes. More research is needed to quantify annual biophysical changes in order to assess cumulative long-term effects of grazing and trampling on vegetation, soil, and hydrology of grazing lands. Modelling such effects is essential for land use planning in this fragile highland environment.

Notes: Abstract. Solutions collected from lysimeters of acid soils can show pH values close to or even above neutral. Laboratory experiments on an acid soil from Burundi were planned to test if denitrification or CO2 degassing might explain such a paradox. In the first experiment, soil profiles were reconstituted in columns and leached with 55 μm Ca(NO3)2 solutions at 30 °C and 4 °C. Two drainage regimes were applied: intermittent suction or no suction at the bottom of the columns. In the second experiment, pH values were measured in solutions drained from different horizons at 30 °C, before and after equilibration with ambient air. Sterilized soil was also tested in the same way. Results from experiment 1 showed that despite the accumulation of water in the bottom of soil profiles when no suction was applied, aeration still existed so that reduction reactions, namely denitrification, are not expected to affect greatly the percolate composition. Indeed nitrate concentration was similar in both drainage regimes and was close to the input value. The pH values in percolates were close to 7 at 30 °C and they dropped to about 5.5 when the columns were at 4 °C. In experiment 2, equilibration of percolates with ambient air resulted in pH increase which was greater for the top horizon (C-rich) but negligible when the soil was first sterilized. These convergent results illustrate the very important effect of CO2 degassing on pH of drained solutions when microbial activity is stimulated at high temperatures, in C-rich soil. This is of prime importance when interpreting results from lysimeter experiments. By chance, this study also showed that large quantities of nitrate can be produced in soil at low temperatures.

Notes: Abstract. As leaching of nutrients and agrochemicals can occur readily in cracking clay soils, which are important to UK agriculture, it is essential to identify management systems for them that can minimize the risk of contaminants reaching surface waters. The long-term Brimstone Farm study has provided considerable evidence on the movement of water and solutes through such soils and offers a unique opportunity to determine the factors influencing these processes. Management procedures, such as subsurface drainage and tillage, which are widely used for the production of cereals in these soil types, greatly influence the risk of contamination. At Brimstone Farm, tillage has been shown to change the hydrology in terms of both water table control and the route of water movement, and to increase the mineralization of nitrogen and the consequent risk of nitrate leaching. Drainage, essential in these soils, also creates a risk of solute losses, especially pesticides. Ways to retain effective drainage yet decrease losses to surface waters are discussed.

Notes: Abstract. Sustaining soil fertility under agricultural intensification and expansion onto marginal lands is a significant challenge in the Nepalese Middle Mountains. In a detailed watershed study it was shown that the overall soil fertility is poor, forest soils display the poorest conditions as a result of biomass removal, and sustaining agriculture is questionable due to the transformation from traditional to multiple cropping systems. Parent material is a significant factor influencing low phosphorus status while insufficient inputs create deficiencies in total carbon, nitrogen and bases. A nutrient budget model was developed to assess inputs, redistribution and losses relative to soil fertility. Yield, input and management data obtained from farm interviews, and soil analysis data were used in the calculation of nutrient budgets. Results from modelling indicate declining soil fertility under rainfed agriculture, forest and rangelands, and marginal conditions under irrigated agriculture subject to intensive cultivation. Nutrient deficits were relatively low for irrigated rice-wheat systems, which benefit from nutrient inputs via sediments and irrigation waters, but the introduction of triple cropping showed greater deficits. Nutrient balances were most critical under rainfed maize production where 94% of the farms were in deficit. Current shortages of organic matter make elimination of nutrient deficits problematic but improvement of composting, biological N-fixation and fertilizer efficiency and reducing erosion were found to be potential options.

Notes: Abstract. During three consecutive years (1993–1995) a split-plot design with three replications was used to study the biological and physical role of mulch in the improvement of crusted soil water balance and its productivity in the north of Burkina Faso. The main treatment was the use of an insecticide, to obtain plots with and without soil fauna (SF and NSF). The subsidiary treatment consisted of four mulch types randomly applied on subplots. These were straw of Pennisetum pedicellatum applied at 3 t ha−1, woody material of Pterocarpus lucens applied at 6 t ha−1 and composite (woody material and straw) treatments applied at 4 t ha−1. In addition there was a control, with no mulch (bare plot). Data on soil faunal activity, runoff, sediment accumulation from wind blown soil, vegetation cover and vegetation dry matter yield were collected on all plots.The biological activity (mainly termites) in mulched plots was the key element in the efficacy of mulching to rehabilitate crusted soil. Water infiltration and dry matter yield were statistically lower on NSF plots than on SF plots and runoff and dry matter yield were not different from the values obtained on bare plots. A significant correlation was found between runoff, all vegetation data and termite-voids. Sediment accumulation due to the physical barrier of the mulch was not found to be a significant factor in the improvement of vegetation performance and the reduction of runoff.

Notes: Abstract. Ammonia volatilization with and without gypsum incorporation was measured in Gujranwala soil (Udic Haplustalf) in an incubation study using different nitrogen fertilizers e.g. urea, ammonium sulphate (AS), calcium ammonium nitrate (CAN), and urea nitrophos (UNP). Nitrogen from different fertilizers was applied at the rate of 200 mg N kg−1 to two sets of soils in plastic bags (1.0 kg soil) and plastic jars (0.5 kg soil). Soil moisture was maintained at field capacity. Application of urea increased soil pH to 9, three hours after its addition. Ammonium sulphate and calcium ammonium nitrate had little effect on soil pH. Ammonium volatilization losses from fertilizers were related to the increase in soil pH caused by the fertilizers. Consequently maximum losses were recorded due to application of urea. Losses through ammonia volatilization were significantly lower with AS, CAN and UNP in descending order. Gypsum incorporation significantly reduced the losses. Therefore, application of gypsum to soil before urea may substantially improve N use efficiency for crop production by reducing N losses.

Notes: Abstract. Precision farming is the process of adjusting husbandry practices within a field according to measured spatial variability. In this review, we explore the prospects for precision farming using the principles that underly conventional soil management and agronomy.The cost-effectiveness of precision farming is determined by the cost of defining zones within fields, the stability of zones through time, the difference in treatment between zones in terms of cost, and the responsiveness of the crop in terms of yield and quality to changes in treatment. Cost-effective precision farming is most likely where prior knowledge indicates large heterogeneity and where treatment zones can be predicted, for example from soil type or field history.Soil related factors are likely to provide the main basis for precision farming because they tend to be stable through time and influence crop performance. In particular, soil mapping may usefully indicate the moisture available for crop growth, organic matter maps may be utilized for precision application of fertilizers and soil acting herbicides, and variation in soil pH can be mapped and used as a basis for variable lime application. However, comprehensive nutrient mapping is less likely to be economic with existing techniques of chemical analysis. The value of yield mapping lies in identifying zones which are sufficiently stable to be of use in determining future practices. Maps of grain quality and nutrient content would significantly augment the value of yield maps in guiding marketing decisions and future agronomy. Interactions between soil differences and seasonal weather are large, so yield maps show considerable differences from season to season. Interpretation of such maps needs to follow a careful, informed, analytical process.Extensive and thorough field experimentation by crop scientists over many years has shown that yield variation arises as a result of a large and complex range of factors. It is highly improbable that simple explanations will be appropriate for much in-field yield variation. However, the capacity to sense yield variability within fields as opposed to between fields, where there are many confounding differences, provides an opportunity for the industry to improve its understanding of soil-based effects on crop performance. This should support its decision taking, whether through precision farming or through field-by-field agronomy.The main obstacle to the adoption of precision farming is the lack of appropriate sensors. Optimal sensor configurations that will measure the specific needs identified by end-users need to be developed.The conclusions reached in this paper probably apply to farming throughout northern Europe.

Notes: Abstract. A lysimeter experiment showed a decrease in maximum concentrations and total losses of the herbicide isoproturon leached from a heavy clay soil where the topsoil had a finer, deeper tilth than with a standard agricultural tilth. Volumes of leachate for the first flow event of the season were also smaller and leaching of bromide was slower. The isoproturon was radiolabelled so that its movement could be assessed using a novel radio-scanning technique. Bypass flow began close to the surface as a scan at 8 cm depth showed that only 0.5% of the total soil area had an activity more than four times the nominal background level. At depths of 10–20 cm, isoproturon was preferentially retained within areas of very fine aggregates. No radioactivity was detected in the scans below 20 cm depth, suggesting little or no retention of isoproturon during transport through the subsoil to the bottom of the lysimeter. Rhodamine-B dye injected to the base of the topsoil (approximately 20 cm depth) was also used to assess flow pathways through the subsoil. The dye spread laterally across the interface between topsoil and subsoil and then penetrated the subsoil through cracks and fissures. Even within cracks, transport of dye frequently occurred through only a very small proportion of the total crack area. The macropore flow model MACRO 4.0 was used to simulate results from the lysimeter experiment. The fourfold decrease in maximum concentrations of herbicide from the finer tilth lysimeter could be predicted by varying only a parameter describing aggregate sizes at depths of 6–24 cm, suggesting that transfer of herbicide between macropore and micropore regions was faster in the finer tilth. Differences in concentrations of bromide could be simulated only by adjusting the soil hydraulic parameters for the fine tilth to reflect a slight decrease in the predominance of bypass flow relative to matrix flow.

Notes: Abstract. Degradation of isoproturon in a heavy clay soil followed first-order reaction kinetics with half-lives at 15 °C of 27 and 208 days in the topsoil and subsoil, respectively. Adsorption when shaken with 3 mm sieved samples of the soil fitted the empirical Freundlich relationship with k values of 3.25 in the topsoil and 1.06 in the subsoil. Adsorption in a static system with different sized aggregates of soil did not reach equilibrium, even after 24 hours contact, and the rate of adsorption was slower with larger aggregates. Following an adsorption period of 24 hours, desorption equilibrium was reached more rapidly with larger (6–10 mm) than with smaller (〈3 mm) aggregates. Adsorption isotherms measured in a static system with a soil:water ratio typical of field conditions in winter also indicated less adsorption than that measured in shaken, laboratory systems with low soil:water ratios. The rate of change in water extractable residues of the herbicide was more rapid than that of total extract-able residues following application of isoproturon to the heavy clay soil in the field. The implications of the results for isoproturon leaching under field conditions are discussed.

Notes: Book reviewed in this article: Land Resources: Now and for the future By A. Young.

Notes: Abstract. In order to optimize the management of the N-fertilizer inputs with drip fertigation on sandy-silt soil under apple tree orchard cultivation, we observed in situ: (i) the N and water soil transfers, (ii) the N levels in all leaves, fruits and annual shoots, and (iii) the root distribution. Then we used a mechanistic one-dimensional model (WAVE, Vanclooster et al., 1994) to quantify the annual parameters of the water and nitrogen balance on a daily basis. The horizontal heterogeneity along the row of the tree-soil-dripper system has been treated with two adjacent compartments: one under the dripper and receiving fertigation and the other outside this zone. N transfers in the tree make it impossible to estimate directly N uptake by roots over time.The simulated N losses were due to equal amounts of N leaching below 0.9 m deep (9 g N tree−1year−1 and denitrification (7 g N tree−1year−1. The simulated losses of gaseous N were localized predominantly in the compartment under the dripper and showed a higher rate of leaching during the period of N input when the wet conditions and the high NO3− concentrations were favourable to denitrification. The N-leaching at 0.9 m depth was greatest outside the growing season and was caused by the extension of the N-inputs after the harvest date. This practice, based on the objective to store nitrogen before the period of dormancy does not seem to be justified.

Notes: Abstract. People in the Southern Highlands of Papua New Guinea cultivate some land semi-continuously within a regime of shifting cultivation; the staple crop is sweet potato (Ipomoea batatas). The fertility of Tropepts, variably affected by falls of volcanic ash, was investigated to give further understanding of how subsistence farmers avoid the soil constraints that commonly prompt abandonment. While organic matter, N and K all decrease significantly with time under cultivation, they do not reach critical levels. Phosphorus also decreases significantly over time, although contents are small throughout. Other nutrients show no significant variation with period of use or abandonment. These findings comply with the diversity of crops cultivated early in the life of ‘gardens’, followed by sweet potato, cultivated as a virtual monocrop in long established ‘gardens’. It continues yielding adequately regardless of decrease in nutrient availabilities, notably because nutrient ratios remain favourable for tuberisation and because of sweet potato's tolerance of small phosphorus concentrations. It appears that burning of vegetation significantly increases available minerals and helps maintain a supply which is adequate for longterm sweet potato monoculture. Similar situations are postulated for other areas of less-weathered soils within the tropics.

Notes: Abstract. An effective fertilizer recommendation system requires information on seasonal, soil-related and cultural variations in soil mineral nitrogen (N) and nutrient requirements of the crop. This can be provided by dynamic N turnover models, such as listed by Plentinger & Penning De Vries (1996). In this paper, we describe a survey of farmer opinion designed to ascertain what farmers want from such a decision support system. Over 100 farmers were surveyed. Surveyed farmers requested that default values be available for all model inputs. Inputs should be entered both by windows-based menu (for clarity) and tabular format (for speed), have user-selected units, and be fully supported by context-sensitive help. The system should have a hierarchical structure allowing access to fixed parameters, and be compatible with commonly used farm recording packages. Recommendations should be provided both for the field (single and optional application rates), and in tabular format across the whole farm. Simulations should be easily rerun using more recent crop and weather data. Turnover processes underlying recommendations should be illustrated by flow diagrams of flux between pools, pie charts of fertilizer fate, bar charts of movement down the soil profile and graphical plots of changes in N status against time.

Notes: Abstract. Ten chalk topsoils (0-25 cm) were repacked into columns in the laboratory. After leaching similar to one year's throughflow in the field, loss of K was equivalent to between 9 and 74kg K/ha. This represented between 3 and 30% of the initial exchangeable K with which loss was poorly correlated. Loss was dependant on the soil solution concentration and was inversely proportional to potassium buffer power.The loss of magnesium in the same columns was between 10 and 22 kg Mg/ha (6-21% of the initial exchangeable Mg). Magnesium loss was poorly correlated with exchangeable Mg.When KCl fertilizer was incorporated into the soils, the increase in leaching of potassium was 1–35% of the K addition. Application to the top of the column resulted in less leaching than when the K was incorporated. Leaching of magnesium was increased by up to 5 kg Mg/ha.Potassium leaching may be delayed by the underlying A/C horizon but pure chalk, with an extremely low buffer power for K, has little ability to retain K. Extremely calcareous topsoils were the most leaky although in practice it is the organic chalk soils on which it is most difficult to attain adequate K levels. On all chalk soils, maintenance of a high K level with K fertilizer is likely to cause unnecessary long-term leaching losses. Annual, rather than biennial, fertilizer applications are to be preferred.

Notes: Abstract. The effects of straw disposal by burning and incorporation on soil and crop nitrogen (N) supply, were investigated on two light textured soils in central (ADAS Gleadthorpe) and eastern England (Morley Research Centre) over the period 1984 to 1995. Nitrogen balance calculations showed that after 11 years of contrasting straw incorporation versus burn treatments, the cumulative N returns in straw were c. 570kg/ha at Gleadthorpe and c. 330 kg/ha at Morley However, these N returns via straw incorporation were not reflected in increased total soil N levels in autumn 1994. There were no differences (P 〉 0.05) between straw disposal treatments in autumn soil mineral N supply, readily mineralizable N or organic carbon. Similarly, there were no consistent differences between the treatments in terms of crop yield, crop N uptake or optimum fertilizer N rates. Fertilizer N applications of 200 kg N/ha/y increased topsoil organic carbon from 1.18 to 1.28% and total N content from 0.091 to 0.102% on the loamy sand textured soil at ADAS Gleadthorpe, but not at Morley. Previous fertilizer N applications increased the quantity of nitrate-N leached in drainage water by c. 20 kg/ha at Gleadthorpe and c. 60 kg/ha at Morley overwinter 1994/95, and by 10–20 kg/ha at both sites overwinter 1995/96. There was some indication overwinter 1994/95 that straw incorporation reduced nitrate-N leaching by 10–25 kg/ha, but there were no differences between treatments overwinter 1995/96.

Notes: Abstract. Formulation of nitrogen balances on farms requires accurate information on all inputs of the nutrient. N2-fixation by legumes, particularly forage legumes, is an important input which is difficult to measure. Simple regression models have been established from the literature for predicting N2-fixation by grass–white clover (Trifolium repens) mixtures using dry matter yields.Linear relationships were obtained between the N2- fixation (Nfix) and the extra dry matter production of mixed swards (Md) compared with pure grass swards. Nitrogen fixation was given by Nfix= A + 0.067Md where A is the intercept having a value of 6.8 for cut swards and -168.1 for grazed swards. A common slope was adopted because the F statistics showed that slopes fitted separately were not significantly different. The value of the negative intercept represents the supply of N to the grazed sward from soil and excreta-derived N. The regression equation for the cut sward gave reasonable predictions (r2= 0.953) of values of N2-fixed for experimental data not used in establishing the relationship. For grazed grass, the approach over-estimated the N2- fixation by an average of 15%.

Notes: Book reviewed in this article: Agricultural Recycling of Sewage Sludge and the Environment By S. R. Smith.

Notes: Book reviewed in this article: No-tillage seeding: science and practice By C. J. Baker, K. E. Saxton & W. R. Ritchie.

Notes: Abstract. The rates of CO2 production and decomposition of 13C-enriched Lolium perenne leaves and roots in soil from the surface five cm of two upland stagnohumic gley soils were measured in laboratory experiments. One of the soils had been limed (pH 6.8) 13 years earlier. The other was unlimed (pH 3.7). Liming increased the rate of CO2 release from soil to which no L. perenne had been added. About 30% of the 13C in L. perenne leaves remained in both limed and unlimed soil after 224 days. By contrast, less 13C-remained in the limed soil amended with L. perenne roots (44%) than in the limed soils (55%). Although the daily rate of CO2 from the plant material-amended soils was initially greater in the improved than in the unimproved soil, it subsequently declined more rapidly.

Notes: Abstract. The characteristics and variability of soils within a 30 ha experimental site in N. E. Nigeria are analysed in relation to tree establishment. Profile description and analyses for some 480 surface samples of the sandy to clayey surface soils from Lake Chad lacustrine sediments provide baseline properties against which any subsequent modifications resulting from agroforestry practices can be assessed and to which initial tree performance can be related. This has been undertaken using principal component and spatial analyses. Inherited soil properties show spatial variations across the site which can be related to the soil textural parameters. The initial survival of trees planted for agroforestry experimentation shows strong correlations with the inherited characteristics of the soil rather than with acquired soil properties.

Notes: Abstract. Field measurements of cumulative infiltration and of the matric potential prior to infiltration were made with double-ring infiltrometers and tensiometers, respectively, on two sandy loams in north-east Scotland. The time to ponding for constant-rate infiltration was also measured in the same infiltrometers by applying water at a constant rate until ponding commenced. Under the range of initial potentials studied (-2 to - 17 kPa), an exponential relation was adequate to describe the relation between sorptivity and initial matric potential. The time to ponding was also strongly dependent on initial matric potential and increased dramatically as the soil became drier. Measurements of time to ponding were in good agreement with values predicted from the theory of Clothier et al. (1981) using values for sorptivity and the A parameter obtained from the cumulative infiltration experiments. Measurements and predictions clearly showed the importance of the sorptivity versus initial matric potential relation in controlling the time to ponding of such sandy soils. These results have implications for determining the generation of runoff and the establishment of stream flows, as well as determining optimum rates and design of irrigation.

Notes: Abstract. Use of either three or six occasions to spread similar total amounts of slurry was investigated over the late winter/early spring period in two years, on plots with underdrainage. Slurry was spread on four 7 m by 25 m plots which were instrumented to allow collection of drainflow and runoff. The ‘mobile water’ pore space allowed transport of a small proportion of applied slurry through the 0.75 m soil profile. Evidence of a polluted ‘mobile water’ pulse occurred after periods of up to 48 hours following spreading, suggesting subsurface rather than overland flow. Timing of the pulse depended on whether subsequent rainfall accelerated the flow The contaminated flow persisted for 6–12 hours. The worst contamination of 39 mg/l NH4+ -N occurred under ‘bypass flow’ conditions, when 52 mm of rain fell during the 48 hours after a 5.2 mm application. Two contributory factors appeared important. The first was the long duration of the high intensity storm and the second was an extended period of severe frost believed to have created fissures associated with frost heave. Making several applications of slurry in amounts less than 35 m3/ha is preferable to fewer larger applications during spring, for cereals on medium to heavy soils. This recognises the likelihood of there being underdrainage on arable land and the optimal use of well-drained, partially frozen ground to avoid compaction by slurry tankers.

Notes: Abstract. The mean extractable sulphur (S) concentration in 315 upland topsoil samples collected in 1988/89 from beneath pasture in NE Scotland was 13 μg S g−1 (range 2–77 μg S g−1). More than two thirds of the samples had S concentrations less than that acceptable for productive soils. Continued decreases in atmospheric S inputs may have increased this proportion subsequently. The analysis of herbage S also indicated that two-thirds of the samples were below 0.2% S. A ‘respirometric index’, namely CO2 produced during cellulose decomposition without added S as a percentage of that produced with added S, was significantly less than 100% in a quarter of the soils. Results of three different extraction procedures suggested that sulphate in the soils was present mainly as free plus adsorbed rather than precipitated forms. Soil extraction identified a significant non-sulphate S fraction, presumably organic S. The variability in extractable S stemmed from a combination of geographical, depositional and local site and soil factors. Extractable S was significantly correlated with soil organic matter content and inversely with soil pH and together these factors explained 37% of the variability. While significant differences in mean concentrations between geographical area, soil association and drainage status were evident, no trends could be observed between the major soil subgroups or with altitude.

Notes: Abstract. We investigated whether a polyacrylate polymer could be used to remediate a soil which had been contaminated with copper for many years. Perennial ryegrass was grown in a loamy sand containing 230 mg ammonium-acetate-EDTA extractable Cu kg−1 and amended with 0, 0.1 and 0.2% of polymer. Growth of perennial ryegrass was stimulated in the polymer-amended soil, especially in the soil with 0.1% of polymer. After plant growth for 177 days, the amount of water extractable copper present in the unamended soil was 17 times that of the original soil. In the soil amended with 0.1% of polymer the level of copper after plant growth was only 0.11 times the amount present in the unamended soil. When the soil was incubated with polymer in the absence of plants, the level of water extractable copper was not reduced. The polymer seems to compete with plants for copper, and to prevent the increase of copper in soil solution brought about by root exudates.

Notes: Abstract. Soils developed on volcanic parent materials have many intrinsic qualities favourable to cropping. However, fertility decreases dramatically when they are badly managed. A short review and case studies from Réunion and Guadeloupe highlight the special characteristics of these soils, and their response to management.The interplay of cropping systems and physical characteristics of Andisols is first considered through the example of Pelargonium and food crop systems in Réunion. Progressive decrease in production and cropping potential shows in falling yields as well as in the overall decline of the system. The example of banana production in Guadeloupe highlights the increase in inputs needed to realise the land's potential and to maintain yields, in particular more tillage and pest treatment.In both cases, these trends are connected to the co-evolution of soil characteristics and cropping systems. They lead to an increase of risks with less security and less scope in the choice of cropping systems. Technical solutions in the form of erosion-control measures, rotation and planting techniques have been developed and prove to be relevant and consistent in their benefit.

Notes: Abstract. Soil classification is a tool for stratifying and generalizing information on soil resources but most systems are tailored to handle only slightly disturbed soil. We tested the applicability of the legend of the FAO-Unesco Soil Map of the World and the new World Reference Base for Soil Resources by classifying at the highest order 831 profiles from a nationwide 7 km grid survey in Denmark, where soils are developed in Quaternary glacial and marine sediments and intensively farmed. Comparison of the variability of pH and % clay +% silt of the master horizons (A, E, B, and C) within and between the major well-drained soil groupings shows that liming, fertilizing and ploughing have produced significantly deeper A-horizons with higher pH, lower % humus and C:N ratios on the two-thirds of the country that is cultivated. ‘Anthropogenic’ mollic and umbric horizons are a common result but the liming causes a random final classification of these surface horizons and, hence, random allocation of the soils in both systems. It separates cultivated soils and their undisturbed equivalents, and results in considerable within-group variation in soil texture. Grouping of cultivated and undisturbed soils, on the other hand, results in wide within-horizon pH ranges for most groups, again compromising the advantage of making useful general statements on the basis of classification.We propose that anthropogenic mollic and umbric horizons should be allowed in any soil group and that ‘anthric properties’ should be used to distinguish between profoundly changed cultivated soils and largely undisturbed soils, hereby constructing a two-tier system within each highest-order soil group. We classified the soils according to this proposal. The results show generally narrower ranges for both pH and % clay +% silt. We evaluated the within-group homogeneity by multivariate analysis of variance of pH, % clay +% silt, % clay, % humus, C:N ratio, exchangeable cations, and CEC. The results (Wilks's Lamda) show a higher degree of group compactness compared to the original FAO and World Reference Base systems.

Notes: Abstract. In dairy farming systems the risk of nitrate leaching is increased by mixed rotations (pasture/arable) and the use of organic manure. We investigated the effect of four organic farming systems with different livestock densities and different types of organic manure on crop yields, nitrate leaching and N balance in an organic dairy/crop rotation (barley–grass-clover–grass-clover–barley/pea–winter wheat–fodder beet) from 1994 to 1998. Nitrate concentrations in soil water extracted by ceramic suction cups ranged from below 1 mg NO3-N l−1 in 1st year grass-clover to 20–50 mg NO3-N l−1 in the winter following barley/pea and winter wheat. Peaks of high nitrate concentrations were observed in 2nd year grass-clover, probably due to urination by grazing cattle. Nitrate leaching was affected by climatic conditions (drainage volume), livestock density and time since ploughing in of grass-clover. No difference in nitrate leaching was observed between the use of slurry alone and farmyard manure from deep litter housing in combination with slurry. Increasing the total-N input to the rotation by 40 kg N ha−1 year−1 (from 0.9 to 1.4 livestock units ha−1) only increased leaching by 6 kg NO3-N ha−1. Nitrate leaching was highest in the second winter (after winter wheat) following ploughing in of the grass-clover (61 kg NO3-N ha−1). Leaching losses were lowest in 1st year grass-clover (20 kg NO3-N ha−1). Averaged over the four years, nitrate concentration in drainage water was 57 mg l−1. Minimizing leaching losses requires improved utilization of organic N accumulated in grazed grass-clover pastures. The N balance for the crop rotation as a whole indicated that accumulation of N in soil organic matter in the fields of these systems was small.

Notes: Abstract. Eight lysimeters, each with a surface area of 0.5 m2 and a length of 60 cm, were taken over mole drains from a Denchworth soil and divided into two groups with either a standard agricultural tilth or a finer, deeper topsoil tilth. They were variously instrumented to measure soil moisture content at three depths and losses of nitrate, a bromide tracer and radiolabelled isoproturon, all of which were followed over a year. Leaching of isoproturon was initiated by artificial irrigation either 1 or 39 days after application. The finer tilth seemed to increase the water-holding capacity of the topsoil, and this resulted in slower wetting of the subsoil, decreased flow volumes from the first events of the season and a delay of approximately four weeks in the time to the maximum concentration of the bromide tracer in leachate. The finer topsoil tilth also decreased maximum concentrations of isoproturon from 29 to 15 μg l−1 following irrigation 1 day after treatment and from 43 to 9 μg l−1 following irrigation 39 days after treatment. Total losses of isoproturon were three times larger with the standard agricultural tilth. Differences were attributed to a decrease in bypass flow through the topsoil with the finer tilth, particularly during events early in the season. There was a small decrease in total losses of nitrate in leachate from the finer tilth compared to that from the standard tilth.

Notes: Abstract. The effects of afforestation on potential nitrification, nitrification and ammonification rates were studied at an experimental site in NE Scotland 4½ years after afforestation of former arable land. The site had been planted with three tree species (Sitka spruce, sycamore and hybrid larch) at three different planting densities, with half the plots treated with inorganic NPK fertilizer. Laboratory measurements of potential nitrification, nitrification and ammonification rates, measured using a perfusion system, were compared between the unforested control and combinations of the various treatments. Differences in soil pH and soil moisture content were also investigated.Potential nitrification rates measured in plantation soils were significantly lower than in the unplanted control soil. Nitrification and ammonification rates were also consistently lower, although these differences were only significant in a few of the treatments. Soils planted with a normal tree density had a tendency to show higher nitrification rates compared to soils planted with a high tree density.The results suggest that afforestation of former agricultural soils may cause changes in important parts of the soil N cycle soon after planting. At this early stage in the life of the plantation this appears to be unrelated to changes in soil pH or moisture content, even though soils beneath the trees are drier. The apparent change may be the result of differences in the soil microbial community associated with the type of organic matter substrate present in the unplanted and planted soils.

Notes: Abstract. Increasing concerns for the financial and environmental impact of the use of broadcast fertilizer by the UK horticultural industry is leading to the development of alternative application techniques, which aim to reduce inputs through improved efficiency. One such technique, ‘starter’ fertilizer, was investigated with drilled and transplanted crisp lettuce (Lactuca sativa) on two fertile peaty soils. Starter fertilizers injected below the seed of the drilled crop, or as spot applications around the planting module, were tested alone and in various combinations with different rates of broadcast fertilizer. The work extended previous findings, based largely on mineral soils, and demonstrated that high yields of iceberg quality lettuce can be achieved with reduced inputs of broadcast fertilizer, and that there can be additional benefits of earlier maturity and improved quality. It is concluded that starter fertilizer can contribute to the development of environmentally beneficial farming practices whilst maintaining the productivity and competitiveness of the horticultural industry.

Notes: Abstract. Ancient forests which have never been under agriculture often have larger ecological and pedological value than later established forests. We made a reconstruction of the land use history of the Meerdaal forest complex in central Belgium since 1759. Soil profiles of 33 recent forest sites and of contiguous forest parcels were examined morphologically by augering to 120 cm depth. pHKC1 was determined on samples from every horizon. The data were analysed by Principal Component Analysis, and the axes were used as a basis for derivation of horizon parameters. Former agricultural land use since 1759 can still be recognized in three soil morphological characteristics: colour of the eluviation horizon, intactness of the horizon containing illuviated clay and thickness of the organic layer. These parameters were combined into a ‘naturalness index’, which differs significantly between ancient and recent forest and can be easily and cost-effectively obtained to assess the degree of man-made disturbance of forests on loess-derived soils.

Notes: Abstract. A long-term lysimeter experiment with undisturbed monoliths studied leaching behaviour and balances of phosphorus (P), potassium (K) and nitrogen (N) during a seven year crop rotation on four types of soil receiving inorganic fertilizers, manure and grass compost respectively. It was shown that application of manure did not lead to any direct change in nutrient leaching, unlike the application of fertilizers to soils of normal fertility. However, soil type considerably affected the nutrient concentrations in the drainage water.Manure applied in amounts equal to the maximum animal density allowed by Swedish legislation slightly oversupplied P and N (0.5–3.5 and 18–38 kg ha−1 y−1 respectively) compared to the crop requirement and leaching losses for most of the soils. The relationship between lactate-soluble P in the topsoil and the concentrations of dissolved P in the drainage water was very strong. However the strength of this relationship was dependent on just one or two soils. P losses from a fertile sandy soil were large (1–11 kg ha−1 y−1) throughout the crop rotation and average crop removal (13 kg ha−1 y−1) plus the leaching losses were not balanced (average deficit 3–6 kg ha−1 y−1) by the addition of fertilizer, manure or grass compost. No decreasing trend was found in the P losses during seven years. However, the K deficit (average 26 kg ha−1 y−1) led to a significant reduction in the leaching trend from this soil. The other soils that had a smaller K deficit showed no significant reduction in the leaching of K.

Notes: Abstract. Guizhou province has one of the most severe soil erosion problems in China, with 44% of its total area affected. Within the province, Bijie prefecture is the most severely eroded with 63% of the total area affected. In recent decades this erosion is mainly caused by man's agricultural and industrial development. Not only is erosion restricting crop production, it is the cause of disastrous floods which recur with a frequency far greater than in the past. Reduced infiltration of rain has led to a third of the wells and a fifth of the streams running dry, depriving people and livestock of drinking water.This unsustainable use of land can only be corrected by a combination of population control, prevention of slash and burn cultivation and return of steeply sloping land to forest and grassland. Greater appreciation of the need for soil and water conservation is an essential part of this process.

Notes: Abstract. When Albania emerged from its seclusion in 1991, the scientific community had its first opportunity to interact with its international counterparts. Soil resource assessment was made with systems developed in the early 1950s, laboratory facilities to provide supporting data were poor, and it was recognized that a new assessment was urgently needed.The country faces a major challenge in reforestation and soil conservation against a background of overgrazing by sheep and goats and clearing of trees and scrubs for fuelwood. Even orchard and olive trees were used as fuelwood during the winters of 1990 and 1991. Since then, gully and rill erosion has accelerated on many of the sloping lands. In addition to reforestation and conservation measures to reduce the pressures on the sloping land, it is necessary to enhance productivity on the fertile valley bottom soils where most of the agriculture is confined. In the recent past, grain yields have declined due to reduced fertilizer use (low purchasing capacity), and poor management practices. More recently productivity has slowly improved, but land degradation, particularly erosion, has visibly increased.USDA Natural Resources Conservation Service in collaboration with the Land Resources Institute of Albania, initiated work on a new national soil map through collation of existing information and field studies. The land unit for land use planning, evaluation, and general management decisions, is the Major Land Resource Area (MLRA). Each MLRA encompasses geographically associated soils, the majority of which have broadly similar patterns ofclimate, water resources, and land uses. The MLRAs presented here are based on the soil map of Albania at 1 : 200 000 scale. The MLRA information provides an overview of the landscape and natural resources. It can be used to assess land suitability for various crops, opportunities to achieve self sufficiency in food production, selection of areas for both field crops and highvalue crops for export, and identification of appropriate farming system technologies. Each MLRA will have a set of degradation processes which can be flagged, therefore each of them becomes a unit for decision making with respect to investments in research and mitigating technologies. The task is far from complete. Appropriate databases are needed to support the decisions that are being made at national level. To complement the MLRA and related database, decision support systems are needed for the important task of developing policy options.

Notes: The binding of metal to humic substances is problematical. The approaches for studying metal binding to organic matter are briefly reviewed. Ion-selective electrodes (Cu2+ and Pb2+) were used to measure metal complexation by a whole peat and an extracted humic acid (HA) fraction. Scatchard plots and calculation of incremental formation constants were used to obtain values for the binding constants for the metals onto both peat and HA. Both the peat and the humic acid had a larger maximum binding capacity for Pb2+ than for Cu2+ (e.g. at pH = 5 HA gave 0·188 mmol Cu2+ g−1 and 0·564 mmol Pb2+ g−1: peat gave 0·111 mmol Cu2+ g−1 and 0·391 mmol Pb2+ g−1). Overall, the humic acid had a larger metal binding capacity, suggesting that extraction caused conformational or chemical changes. The binding constants (K1) for Cu2+ increased with increasing pH in both peat and humic acid, and were larger in the peat at any given pH (e.g. at pH = 5 HA gave log K1= 2·63, and peat gave log K1= 4·47 for Cu2+). The values for Pb2+ showed little change with pH or between peat and humic acid (e.g. at pH = 5 HA gave log K1= 3·03 and peat gave log K1= 3·00 for Pb2+). In the peat, Cu2+ may be more able to bind in a 2:1 stoichiometric arrangement, resulting in greater stability but smaller binding capacity, whereas Pb2+ binds predominantly in a 1:1 arrangement, with more metal being bound less strongly. Whole peat is considered to be more appropriate than an extracted humic acid fraction for the study of heavy metal binding in organic soils, as this is the material with which metals introduced into an organic soil would interact under natural conditions.

Notes: Excess salts may be removed from soil by leaching, but ponding water on the soil's surface and allowing infiltration requires large quantities of water. During such leaching water flows preferentially through macropores between aggregates, while the flow within aggregates is much less. Consequently, solute within aggregates is removed much more slowly, thus decreasing overall leaching efficiency. For this reason intermittent ponding can be more efficient because it allows time for solute to diffuse to the surfaces of aggregates during the rest period and subsequently be removed in macropore flow. We explored solute transport in aggregated soils under intermittent leaching in three ways: theoretically, by laboratory experiments on columns of porous ceramic spheres as analogues of aggregates, and by simulation. Solute movement during displacement is described by the mobile-immobile convection-dispersion equation. During the rest period flow ceases, and solute redistributes within the aggregates by diffusion, the key variable being the effective diffusion coefficient, De of the solute in the aggregates, and longitudinally by diffusion within macropores (though this was ignored in the simulation). We estimated De for our porous spheres from observations of solute outflow into finite volumes of stirred distilled water. The theory was validated against experiments on saturated columns for different aggregate-size distributions, flow velocities, and displacement and rest periods, with most parameters estimated independently. Experiments and simulations showed that water savings of 25% were possible under our laboratory conditions, increasing as aggregate size, flow velocity and duration of rest period increased. The potential of intermittent leaching in the field is considered.