ALBERT

Notizen: 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.

Notizen: 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.

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

Notizen: 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.

Notizen: 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:

Notizen: 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.

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

Notizen: 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.

Notizen: 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.

Notizen: Abstract. England and Wales have 155 314 1 × 1 km squares, of which 140049 have more than 50% soil cover. The total soil organic carbon content, based on the dominant soil series and dominant land cover type, is estimated to be 2773 × 106 t C. Scotland has 84929 1 × 1 km squares, of which 82 420 have a nominated dominant soil series. The total soil organic carbon content is estimated to be 19011 × 106 t C, 6.85 times the total organic carbon content of the soil of England and Wales. The total organic carbon content of the soil of Great Britain is estimated to be 21 784 × 106 t C, of which 87% is in Scottish soils and 75% is in Scottish peats.A map of the mean soil organic carbon content of 10 × 10 km squares of the National Grid using classes of equal range illustrates the narrow range of organic carbon contents of the soils of England and Wales and the dominance of organic carbon in Scottish soils. A map using the same data, but with classes of unequal ranges increasing in size with increasing carbon content, is better for showing detailed differences within England and Wales.

Notizen: Abstract. Land cover data from the June agricultural census of England and Wales have historically been published annually at the parish level. This level of spatial resolution masks heterogeneity of land use within parishes, limiting the value of the data for detailed spatial analyses. However, variation in land characteristics across parishes can be used to model variation in land cover, thereby allowing the spatial basis of the census data to be transformed. This procedure, referred to as areal interpolation, is illustrated using two land classification systems based on soils for a study area in northern England. The results indicate that the spatially transformed data offer a better description of the distribution of land covers than that provided by the raw census data. They also demonstrate the extra value that can be obtained by combining extant data sources within a GIS framework. Potential roles for areal interpolation in environmental modelling and policy formulation are discussed briefly.

Notizen: Abstract. The disposal of water treatment sludge produced when turbid water is treated with flocculants (alum and polyDADMAC) and filtered for clarification is becoming increasingly expensive in South Australia. The physical and chemical properties of the sludge suggest that it might be used as a plant growth medium, and a glasshouse experiment compared the growth and elemental composition of broad beans in both alum and polyDADMAC sludge applied at different rates.Dry matter production differed significantly between treatments. Poly + Fertilizer (F) and Poly 4%+ F produced the most dry matter. The Alum + F treatment produced significantly less dry matter than the Poly + F treatment but it was not significantly different from the control. The difference in plant growth between the pure poly and pure alum treatments resulted from increased availability of the fertilizer phosphorus in the poly sludge and the supply of some potassium and nitrogen by the poly sludge. Fertilizer was required for optimum plant growth. Greater rates of fertilizer may be required if alum sludge is to be used as a growth medium, than if poly sludge is used.There was no evidence that aluminium toxicity would be a problem if water treatment sludges are used as growth media. The physical properties of the sludges (i.e. water holding capacity, drainage characteristics and structural stability) are probably more important than their inherent nutrient levels, although poly sludge does supply some nitrogen and does not fix phosphorus to the same extent as alum sludge.

Notizen: Abstract. Four field experiments were carried out on cultivated shallow fen peat overlying acid gyttja (lake mud) soil. The accessibility of the generally ample supply of physically available water was restricted by a limited root depth caused by low pH and high levels of aluminium in the subsoil. In order to improve the nutrient status and the crop water supply of the soils liming, deep cultivation, P-fertilization and irrigation were tested in field experiments comprising these four main treatments and their combinations. Liming and P-fertilization of the topsoil, irrigation and deep cultivation in combination with deep liming improved crop yields. Deep cultivation without liming had a negative effect on yield in most years.

Notizen: Abstract. The effect of liming and deep cultivation on soil properties and root development was investigated in two cultivated shallow fen peats resting on acid gyttja (lake mud) soils. Root growth was in general dependent on soil pH and aluminium content of the soil. A soil pH (H2O) below 5 adversely affected roots and a pH below 4 severely restricted root growth. Liming of the topsoil or the subsoil and to some extent deep cultivation improved root growth. Increased rooting depth made it possible for plants to utilize soil water to a greater depth in the profile and to support a larger crop yield.

Notizen: Abstract. Flow and nitrate concentrations were measured weekly for four years at twelve stream-water monitoring sites in a catchment in the English Midlands designated as a Nitrate Advisory Area. Farm surveys and satellite images have provided soil and land use information. Measurements show the nitrate load to be dominated by discharge, with large variability due to differing weather conditions from year to year. Within-year variability in nitrate concentrations is also related to weather conditions, with high concentrations when field capacity is reached if this occurs late in the year. There is also clear evidence of dilution of nitrate during intense storms. The effect of changing weather conditions makes it impossible to identify catchment-scale changes in leaching due to changes in agricultural practice over a period as short as four years. Measurements from a major spring in the catchment show an increasing trend in nitrate concentrations through the period. There is some evidence that the greatest N leaching to streams in the catchment is associated with intensive grassland on soils which are naturally poorly drained.

Notizen: Abstract. At De Marke experimental farm, data on water and nitrogen flows in the unsaturated zone were gathered on two grazed pastures on sandy soils during the years 1991 to 1994. These provided a basis for calibration and validation of simulation models. The different levels of nitrate-N concentrations of the two plots could largely be explained by differences in crop uptake and simulated denitrification as influenced by different groundwater levels. The irregular distribution of excreta was taken into account by a simulation study quantifying the variability of nitrate-N concentrations under a grazed field. The resulting distribution of simulated nitrate-N concentrations explained the average and peak values of the measured concentrations. Temporal variability of weather was used to assess the nitrate leaching risk under urine patches deposited in either July or September. At site A the probability of exceeding the EC-directive by drinking water (11.3 mg/1 nitrate-N) under a urination deposited in either July or September was respectively 10 and 25%. The average field concentration at this site will hardly ever be a high risk for the environment under the current farm management. At site B the EC-directive will be exceeded under any urine patch in almost 100% of the years, affecting the field average concentration. In field B careful grazing management would result in less nitrate leaching, but the environmental goals would not be reached.

Notizen: Abstract. A field experiment on a coarse sand (1987–92) was conducted with spring barley (Hordeum vulgare L.), in order to evaluate the effects of increasing N fertilization on nitrate leaching under temperate coastal climate conditions. The N fertilizer levels were 60 and 120 kg N/ha. The experiment was conducted on a 19-year old permanent field trial with continuous spring barley, initiated in 1968, and included treatments with ploughing in autumn or spring, with or without perennial ryegrass (Lolium perenne L.) as a catch crop undersown in spring. Prior to 1987, the low and high levels of N fertilizer were 70 and 150 kg N/ha, respectively. To calculate nitrate leaching, soil water samples were taken from a depth of 0.8 m using ceramic cups. The average annual nitrate leaching from plots with 60 and 120 kg N/ha was 38 and 52 kg N/ha/y, respectively. The increased leaching associated with increasing fertilizer application was not caused by inorganic N in the soil at harvest, but rather by greater mineralization, mainly in autumn. Growing of a catch crop was relatively more efficient for reducing nitrate leaching than a long-term low fertilizer application. A 50% reduction in N application decreased average yield by 26%, while nitrate leaching decreased by 27%.

Notizen: Abstract. Whey, the liquid byproduct of cheese production, can improve the physical condition of sodic soils or those susceptible to erosion by increasing their aggregate stability. The effects of whey on soil hydraulic properties, however, are not known. In this experiment, we used tension infiltrometers to determine whey effects on infiltration rates of water (at suctions ≥ 30 mm of water) and unsaturated hydraulic conductivities of Ap horizons of a Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthid) after a winter wheat crop. In the summer of 1993 near Kimberly, ID, USA, liquid whey was flood-applied at either 0, 200,400, or 800 t/ha to plots planted to wheat the previous September. At suctions of 60 and 150 mm, infiltration rates decreased linearly by about 0.7 μm/s with each additional 100 t/ha of whey applied. As whey applications increased, hydraulic conductivities at 60 mm suction increased slightly but as applications exceeded 400 t/ha decreased significantly. We concluded that summer whey applications up to 400 t/ha would not adversely affect surface hydraulic properties.

Notizen: Abstract. The potential for using coal-derived humic substances to improve the available water holding capacity (AWC) and aggregate stability of typical Mediterranean soils was evaluated in the laboratory using an agricultural surface (0–20 cm) soil from each of three regions of Italy, (Sicily, Tuscany and Venetia) and five rates of humic acids (HA), 0,0.05,0.10,0.50 and 1.00 g/kg. There were significant (P 〈 0.05) differences between the field capacity (FC), permanent wilting point (PWP), and available water capacity (AWC) values of the controls and those treated with 0.05 g/kg of the HA. Beyond this rate, differences in these properties were not significant. At the 1.00 g/kg HA rate, the relative improvements in AWC over the three controls were 30%, 10% and 26%. Low rates (0.05 to 0.10 g/kg) of HA were also needed to obtain a 40 to 120% improvement in aggregate stability of these soils relative to the controls. These results indicate that the addition of highly humified organic matter such as coal-derived humic substances can improve the structural and water retention properties of degraded arable soils. However, since there is not yet any direct evidence that these humic materials can ameliorate soils under field conditions, field studies will be needed to validate these results.

Notizen: Abstract. A study of soil water erosion was undertaken between 1982 and 1986 in 17 areas of lowland England and Wales. Air photographs were taken annually, these were checked to identify erosion events and a sample of 392 eroded fields visited between 1983 and 1986. Erosion was most common in fields drilled with winter cereals (39% of cases), which was the crop considered by farmers to be at greatest risk of erosion. Estimated crop losses were greater than 10% for only 5% of fields. ‘Clean up’ costs were incurred on 15% of the fields studied. Attempts at contour ploughing and planting/drilling appeared to result in more severe erosion, than working up and down the slope. Farmers considered that the main reason for erosion on their farms was arable cropping, and the presence of compacted wheelings/tramlines. Fields where hedges had been removed in the last 20 years suffered from erosion marginally more frequently than other fields. Field slope alone was not found to be a major factor in the occurrence of erosion, with almost 60% of erosion events on slopes of less than 7°. Erosion occurred at least every other year in half the fields studied.

Notizen: Book reviews in this article: Soil Resilience and Sustainable Land Use Edited by D. J. Greenland and I. Szabolcs.

Notizen: Abstract. Using the simulation model MACRO, this paper investigates the likely consequences of reduced irrigation inputs on the water and salt balance and crop growth in a drained, saline clay in a Mediterranean climate (Marismas, SW Spain). The model was first successfully validated against field measurements of the soil water and chloride balance, water table depths and drain outflows in the 1989 growing season. Three-year simulations were then performed assuming two different irrigation applications (60 and 75% reductions from the 1989 amount) and two different frequencies (12 or 6 irrigations per growing season). The model predictions suggested that reduced irrigation may lead to up to a 15%) increase in the chloride content of the soil profile after 3 years. Also, despite overall reductions in water discharge, slight increases in chloride leaching via field drains (c. 4 to 8%) were predicted. The model demonstrated that encroachment of salt into the soil profile may he exacerbated by the non-equilibrium nature of water flow and solute transport (‘by-passing flow’) in structured clays. With reduced water supply for irrigation, more frequent applications may give marginally better crop yields for the same quantity of irrigation but at the expense of slightly increasing salt concentration in the root zone.

Notizen: Abstract. A model was developed to estimate daily evapotranspiration and root zone soil moisture changes appropriate for scheduling irrigation, incorporating a modified version of the Penman-Monteith equation.The model was field tested during 1992–94, for potatoes and sugarbeet, by comparing modelled root zone soil moisture changes with field measurements taken using neutron probes. The study confirmed the accuracy of the model when predicting crop water use and soil moisture change. Linear regression of measured versus modelled data exhibited a slope of 0.99 and an intercept close to and not significantly different from zero. The relationship accounted for 80% of the variation.

Notizen: Abstract. Regular application of slurry manure in large quantities is thought to degrade soil structure and increase erodibility. One hypothesis links this to the large input of potassium which increases the exchangeable potassium percentage (EPP) and, thereby, dispersion. The effect of EPP on erodibility was quantified in three experiments. In the laboratory, eleven rainfall experiments were conducted using a silty topsoil from a typic Hapludalf which was fertilized to EPPs of 4 to 18%. Field rainfall experiments on 22 Inceptisols and Alfisols were used to examine whether the long-term application of monovalent cations (Na+, K+ and NH4+) with slurry manure had changed soil properties, especially erodibility. In addition, erodibilities of 32 soils determined with natural and simulated rains were taken from literature. The experiments on these 65 soils together covered a wide range of soils, slopes and rainfalls. Dispersion by a large percentage of highly hydrated ions (K+, Na+) reduced the infiltration rate faster, caused runoff up to 5 min earlier, and increased sediment concentrations by 15g/l compared to low EPP soils. These changes increased soil erodibility of the Universal Soil Loss Equation (USLE) by 0.021 t × h/N × ha (where N = Newtons) for each 1% increase in EPP + ESP (exchangeable sodium percentage). The ESP contributed little to this increase as ESP was less than 1/10 of EPP in the experiments.Fields with long-term manure application had similar chemical, physical and microbiological soil properties as fields without slurry manure except for slightly greater pH (+ 0.6) and P (+ 17 mg/kg) values. We conclude that, as long as the potassium input and output are balanced, the long-term use of slurry manure does not increase erodibility.

Notizen: Abstract. A model was developed to predict evapotranspiration and soil moisture changes, which could be used either for scheduling irrigation or crop water-use studies. The general form of the model is reported here, and its validation for sugarbeet and potatoes is described in a subsequent paper. The soil characteristics required are depth of topsoil, texture or available water capacity of topsoil and subsoil, and whether a significant slope exists. The plant characteristics required are species and planting date. Meteorological data used to calculate potential evapotranspiration are obtained from the Meteorological Office synoptic network, but local rainfall data are preferred.The model estimates potential evapotranspiration of a reference crop, and uses this to model canopy and root development for all crops at each location. Available options allow for observed data on canopy or root development to be incorporated into the simulations. Estimates of potential evapotranspiration for each crop are then adjusted to allow for the effects of water stress, taking soil characteristics, root depth and evapotranspiration demand into account.The model enables growers to reduce the risks of under- or over-watering their crops and has proved successful in irrigation management.

Notizen: Abstract. A land evaluation using unsophisticated data successfully predicted yield ranges of various crops in Burundi. Yields of wheat, pea, bean, maize and potato predicted from data for climate, soil and land use technology were compared with observed yields from farm trials and from seed station and research station trials. The predicted range of yield for each crop suitability class enclosed the mean farm yields 13 times out of 16 and yields on seed stations and research stations 10 times out of 15 and 14 times out of 21 respectively. The variability of the observed yields exceeded the predicted range of yields. The method is considered as validated. The method appears to be applicable for multi-year studies at a broad scale, but yield variation according to the weather from year to year is not accounted for. The variances of the yields on farms are greater than the variances in seed station and research station trials.Since the method predicts correctly the mean regional farm yields, it could be useful for land use planning, research into optimal regional cropping specialisation, studies on food policy, and for evaluation of economic return and sustainability of different crops.

Notizen: Abstract. Usual residue-management options are to remove the residue, use it as mulch with or without undercutting or to incorporate it into the soil. While the role of surface mulch in evaporation has been widely studied, the information on the effect on evaporation of mulch with undercutting or residue incorporated into soil, particularly in relation to soil type and evaporativity (Eo) is lacking. We studied the effect of wheat straw used in various ways on the course of evaporation loss from soil columns with three soils at Ludhiana, India and one soil at Bushland, Texas, USA, under two Eo's Energy-limited evaporation rates under mulch (Eom) followed the soil-specific relation Eom/Eo= a e(bRes+cEo), where Res is residue rate t/ha and a, b and c are constants; Eo, is expressed in mm/d. In an effort to model the total evaporation (CE) during the energy-limited stage ‘U’ was obtained from appropriate CE versus time curves and (CE-U) was regressed over (t - ti)0.5 to obtain the slope ‘α’ (Ritchie 1972) for the soil-limited evaporation stage. The observed ‘U’ was independent of mulch rate and Eo but was strongly affected by soil type, Values of ‘α’ decreased with increase in mulch rate and decrease in Eo and coarseness of soil.The otherwise short lived benefit of evaporation reduction with mulch per se, which peaked after a few days was maintained when residue was mixed with soil at the stage when evaporation reduction reached a maximum; this benefit continued for several weeks. Cumulative evaporation values computed from ‘U’ and ‘α’ agreed closely with the observed values under straw mulch for loamy sand and clay loam soils and for ‘undercut’ and ‘residue mixed’ treatments on all soils regardless of Eo, and for all situations under small Eo. However, for sandy loam and silt loam soils under Eo of 10 mm/d, the modified square root of the time function of Jalota et al. (1988) gave a better fit.

Notizen: Abstract. Soil microstructures and biological activity were studied in thin sections of Culluna heathland soils subject to periodic burning. Freely drained Brown Podzolic soils from a species-rich heath at Dinnet Muir, Aberdeenshire, Scotland were compared with shallow Humo-ferric Podzols with a thick humus layer (5–10 cm) supporting a species-poor heath at Balmenach, Aberdeenshire.Structures with greater porosity occurred in all Dinnet soils and the most recently burned Balmenach soil. Burning led to an increase in soil porosity which gradually disappeared after a period of 2–3 years. Soils of the recently burned site had more enchytraeid worms than those burned ten years previously. Most of the Dinnet soil samples were dominated by extremely fine granular structure which could have been produced by flocculation of well decomposed organic matter or by enchytraeid worms. In recently burned sites the increase in soil macro- and microbial activities may lead to the formation of composite structures.Regular burning every 10–15 years has been the land management practice in Scottish heathlands to ensure the production of fresh browse of nutritious heather shoots for herbivores. The near-ground microclimate and regeneration mechanisms of heathland plants are well adjusted to the periodic disturbance by fire. We found that the gradual decrease in surface soil porosity over time can be restored by prescribed burning. Soil structure and the distribution and continuity of pores in the soil profile directly affect soil water movement and retention. These factors have important ecological implications for post-fire vegetation recovery.

Notizen: Abstract. Simulated estimates of crop yield were made for rainfed rice in a 50 ha dryland rice area. The aim was to investigate how soil units and management units of different sizes with different yields could be used to obtain values for areas of land. Two procedures were applied. First, yields were simulated at six sites, that were representative of six soil mapping units. Second, yields were simulated using soil information from 133 auger sites, and were interpolated over management units using block kriging. Differences between the two procedures for the total area and for a test set of 22 additionally sampled locations were small. A 60% increase in precision was achieved when relatively large management units were defined.A Geographical Information System was used to identify areas with greatest yield potential for rainfed dryland rice. Statistical analysis showed that the six soil units could be grouped into three yield classes. The largest yields were obtained for a sub-area comprising 11% of the survey area which was associated with a slowly permeable Bg horizon in the soil profile.It was concluded that the best procedure for the spatial interpolation of simulated rice yield should be based on preliminary simulation of crop yields. A sensitivity analysis of the impact of weather variability and soil heterogeneity on the variation of yield was useful to detect the importance of their contributions. The procedures developed in this study are of value in obtaining a reliable estimate of average yield, and can consequently be used for associated cost-benefit calculations.

Notizen: Book reviews in this article: Soil Conservation and Silviculture By J. Dvořák & L. Novák (editors). Translated by V. Sochor. Environmental Soil Biology – 2nd Edition By M. Wood.

Notizen: Abstract. Soil profiles, first sampled between 1963 and 1973, were resampled in 1991 in an upland area with modertely high deposition of pollutants. One hundred horizons from 32 profiles, representing 10 different soil subgroups were analysed for pH and seven variables related to pH, using the same laboratory methods on both sampling occasions. To allow comparisons to be made with results obtained with these old methods, analysis of the 1991 samples was repeated for some determinands using the methods currently used in the analytical laboratory. Organic and A horizons show a consistent increase in acidity between samplings. Although brown soils and lithomorphic soils have increased in acidity throughout their depth, gleys and podzols have decreased in acidity at depth, probably because of poor water transmission downwards into these horizons. Correlations with other determinands suggest that the dominant process in the soils is leaching of basic cations and their replacement on exchange sites by protons and probably aluminium ions. A cause of the increase in soil acidity is likely to be the deposition of atmospherically transported pollutants.

Notizen: Abstract. Currently there is growing interest in the restoration of drained peatlands in Britain. In order to investigate some of the effects of changes in land management practices on the biogeochemistry of peatlands, a field experiment was designed to manipulate the hydrological conditions in a naturally drained acid gully mire in Mid-Wales. We report preliminary results of the effects of experimentally rewetting the mire on the hydrochemistry of bromide in the peat-water. Results show that rewetting had a dramatic effect on the concentrations of bromide, which increased substantially. Peak values approached 1 mg/dm3 in some samples following rewetting, compared with typical values 〈 0.05 mg/dm3 under the drained conditions. Bromide was positively and significantly correlated with Dissolved Organic Carbon (DOC) in the peat-water, which suggests that Br- is derived from breakdown of organic matter in the reducing conditions following rewetting. The bromide mobilized by rewetting may be leached out of the system and/or re-assimilated by the wetland vegetation. Further monitoring is needed to determine whether the observed hydrochemical response of bromide to rewetting of the mire has any longer-term effects.

Notizen: Abstract. Monoculture winter barley was grown for 5 years with 80 or 160 kg/ha of fertilizer nitrogen (N) and established by either shallow cultivation (straw removed) or ploughing (straw incorporated) in a replicated 2 ± 2 split plot experiment. The lower N rate reduced average grain yield from 6.85 t/ha to 5.61 t/ha. The cultivation/straw disposal system had no effect on yield. Halving the N rate reduced the amount of N removed in the crop by an average of 40 kg/ha and reduced the amount of nitrogen leached by 11 kg/ha per year. Using a shallow cultivation system for crop establishment, following the removal of straw, initially reduced N leaching compared to ploughing in the straw, but in the later years of the experiment losses were similar. Over the five years the full N rate with ploughing system resulted in a small positive nitrogen balance of 66 kg/ha, but all other treatment combinations resulted in a negative balance.

Notizen: Nine different techniques were used to record the initial change in the physical and hydrological properties of a freshly tilled soil surface following successive cycles of wetting and drying. The study was made in the field on a sandy clay loam soil ploughed and harrowed and then exposed to three simulated rainfall events of 76 mm/h for 15 minutes. Although the degradation of the soil surface increased with each successive rainfall, the most significant changes were observed after the first rainfall. Qualitative observations of clod size distribution and crust development provide a good indication of the early stages of soil surface degradation. Complementary physical data were quickly obtained using a hand held shear vane. These techniques are simple and robust enough that they can be used in on-farm research programmes, where resources, both human and technical are at a premium. Tension infiltrometry provided hydrological information that complemented the physical information provided by the above techniques, but is not as simple.

Notizen: Abstract. To study the change in soil organic carbon (SOC) since it was recorded during the Belgian National Soil Survey some 40 years ago, we recently revisited 939 locations still under use as arable land. The study area comprised almost the entire province of West Flanders (about 3000 km2) characterized by profound changes in its arable land management.Taking the increased ploughing depth (by 9.8 cm on average) into account, a significant (P= 0.001) increase of the SOC content by 0.2% on average was found. Expressed as an amount, the SOC in the topsoil rose by 9.3 t/ha on average, representing an increase of 25%. This is comparable with the conversion of arable land into grassland for 2 to 3 decades.Geostatistical tools were used to map the SOC at the two times of observation. These showed that most of the spatial variation occurred within about 4 km. Since the community level is the smallest spatial resolution on which agricultural statistics are gathered officially, a detailed modelling of the change in SOC was impossible. However, by selecting communities with extreme changes in SOC, we found indications that the major source of increase in SOC was due to the large increase in pig breeding.

Notizen: Abstract. The understanding of nitrogen mineralization is central to providing good advice to ensure that nitrogen (N), from whatever source, is utilized by crops as efficiently as possible to minimize pollution. We have reviewed how mineralization is accounted for in current advice. It is clear that there is at least a qualitative understanding of the effects of soil and crop management on N mineralization and N supply, which has enabled the development of Codes of Good Agricultural Practice and fertilizer recommendations systems, based on sound scientific principles. However, to refine advice there is a need for a better quantitative understanding.Although soil organic matter (SOM) is a major source of N for crops, we are unable adequately to predict fertilizer requirement as affected by mineralization of SOM. Nitrogen returns from crop residues can vary considerably between fields; the provision of better field specific advice is restricted by our inability accurately to quantify this variability. The qualitative controls on the amount and timing of N release from ploughed grass are known, but better quantification of mineralization/immobilization over both the short- and long-term and better understanding of the relationship with sward age, inputs and management are essential. Much N can also be released from pasture and lost to the environment, especially where long-term leys have been grazed and there is a need to quantify the changing balance of mineralization and immobilization with the age of sward and N input. Whilst the overall principle of cultivation affecting mineralization is well known and appreciated, little is known about the mechanisms and quantification is only possible for a comparison of such extremes as ploughing and direct drilling.

Notizen: Book Review in this ArticlesSoil Conservation (Third Edition) By N. Hudson.Conserving soil resources: European perspectives. Selected papers from the First International Congress of the European Society for Soil Conservation Edited by R.J. Rickson.Soil and water management systems, 4th edition By G.O. Schwab, D.D. Fangmeier & W.J. Elliot.

Notizen: Abstract. In response to the European Community Nitrate Directive (91/676) a catchment scale Geographical Information System (GIS) model of nitrate leaching has been developed to map nitrate vulnerability and predict average weekly fluxes of nitrate from agricultural land units to surface water. This paper presents a pilot study which investigated the spatial variability of soil nitrates in order to: (1) define an appropriate pixel size for modelling N leaching; (2) quantify the within-unit variability of soil nitrate concentrations for pasture and arable fields; and (3) assist in the design of an efficient sampling strategy for estimating mean nitrate concentrations. Soil samples, taken from two 800 m transects in early September 1994, were analysed for water soluble nitrate. The arable soils had a mean nitrate-nitrogen concentration of 0.693 μg/g (S.E. 0.054 μg/g) and the pasture soils had a higher mean nitrate-nitrogen concentration of 0.86 μg/g (S.E. 0.085 μg/g). Spatial variability was investigated using variograms. The pasture data had a weak spatial relationship, whereas the arable data exhibited a strong spatial relationship which fitted a spherical variogram model (r2 0.87), with a range of 40 m. A pixel size of 40 m is suggested for nitrate modelling within the GIS based on the arable variogram and an improved sampling strategy for model validation is suggested, involving bulking sub-samples over a 40 m grid for estimating mean nitrate concentrations in combined land use and soil units.

Notizen: Abstract. An area of about 24 km2 in arable East Lothian, Scotland, was examined for soil erosion by water following a severe rainstorm in October 1990. Significant erosion was found in only 10 fields out of 26.5 in an area where topography, soils and cropping suggest a high erosion risk. Doubt is cast on some assessments of the widespread risk of significant soil erosion by water in arable areas of the UK.

Notizen: Abstract. Proposed restrictions on the disposal of sewage to the marine environment means that alternative land based outlets are required in the UK. Commercial forestry represents a significant land use that could receive and benefit from the application of sewage sludge, to overcome the generally poor soil nutrient status. The oligotrophic and sensitive nature of surface waters in many afforested areas requires that the environmental consequences of the widespread use of organic fertilizers in forestry are carefully considered. This paper compares the effects of an N and P fertilizer with that of sewage sludge on the nutrient content of foliage in a pole stage Scots pine (Pinus sylvestris) forest and of nutrient fluxes in soil. Both conventional fertilizer and sewage treatments had significant but differing effects on the availability and leaching of the major nutrients, especially N and P. Evidence for increased nitrification and nitrate production with time was apparent for both treatments. Fluxes of N and P in mineral horizon leachate were consistently smaller than those from the overlying organic horizon. Foliar nutrient concentrations after one year were significantly higher (P 〈 0.01) in all of the treatments, and conventional fertilization with urea produced a significantly higher foliar N concentration than that measured in the sludge-treated plots. There was no evidence for appreciable N or P leaching from the site within a year of sludge application.

Notizen: Abstract. An easy-to-use simulation model was developed with the aim of improving fertilizer practice when crop residues are incorporated instead of removed. It was tested against data from a well-monitored N fertilizer experiment in which three successive brassica crops were grown followed by barley.Experimental findings included: (a) that fertilizer-N greatly increased yield of 3 crops without increasing residual soil mineral-N at harvest unless supply exceeded crop demand; (b) that, by contrast, fertilizer-N increased both yield of and residual soil mineral-N left by the remaining crop throughout the range of applications; and (c) that at each harvest the apparent disappearance of fertilizer-N by immobilization and other processes was almost proportional to fertilizer-N. These phenomena were simulated by the model.Overall the model gave estimates of soil mineral-N, plant weight and % N in the crop for each crop that were either in close agreement with or linearly related to the measured values. Deviations from this pattern are shown to result almost entirely from experimental error. In addition the model gave simulations of the time course of soil mineral-N and soil water that were in good agreement with measurement.Simulations with the model indicate that appreciable benefits from residue incorporation of crops will only be obtained when fertilizer-N is also applied, unless plant masses at harvest are small.

Notizen: Abstract. The MACROS crop model was evaluated for its utility to generate information on land suitability for dry season peanut cropping based on water availability at the regional scale in Khon Kaen Province, Northeast Thailand. The model was specific for the condition where crop growth is limited by water stress, and evaluated using both calibration and validation phases in sequence. In the model calibration, data sets from one peanut field experiment were used to calibrate some parameters to obtain the best agreement between experimental and simulated results. The model validation, in this study, consisted of a ‘validation A’, with emphasis on the accuracy and a ‘validation B’, with emphasis on the usefulness and relevance of the model. In the model validation A, data sets from peanut field experiments were used to validate the model under different conditions. Satisfactory agreements were found between the dynamics of observed and corresponding simulated values of shoot dry weight in every condition involved in this validation study. Also the simulated pod yields agree well with the field data. For the validation R, the model was further validated using data from 36 farm trials conducted at 5 different test sites. A high positive correlation (r= 0.91) existed between observed and simulated pod yields. Because of these satisfactory agreements between observed and corresponding simulated values, it was concluded that the model is valid and can be applied to Khon Kaen Province.

Notizen: Book reviews in this article: Soils and Environment By S. Ellis & A. Mellor. Soil Erosion Research Methods Edited by R. Lal. Agriculture and Environment: Bridging Food Production and Environmental Protection in Developing Countries Edited by Anthony S.R. Juo and Russell D. Freed. Soil Management in Sustainable Agriculture Edited by H.F. Cook and H.C. Lee. Soil Nutrient Bioavailability—2nd Edition By Stanley A. Barber. Soil fertility decline under sisal cultivation in Tanzania By Alfred E. Hartemink.

Notizen: Abstract. Information about the soil fertility status in irrigated ricelands at regional scales (1:50 000–1:250 000) is commonly not contained in classical soil maps. To assess the agronomic suitability of two different reconnaissance soil maps, we conducted a detailed soil survey in the Nueva Ecija province, Philippines. Soil samples were collected from 384 farmers' fields, and soil properties were measured for topsoil and subsoil samples. For most soil properties, a soil map made in 1940 (1:125 000) had within-map unit variances that were smaller than the total variance, whereas a new soil map of 1992 (1:50 000) did not significantly reduce the within-class variance. In both soil maps, classification into mapping units accounted for 0–40% of the variance of 14 agronomically important soil properties and large within-map unit variabilities were found. Underlying strategies of classical soil survey supported the partition of variance for relatively stable soil properties, such as soil texture, CEC, and organic matter. If reconnaissance soil maps are used in quantitative land evaluation studies, existing maps require upgrading by adding quantitative information about relevant soil properties and their within-map unit variability The sampling demand for upgrading a reconnaissance soil map was large, but pedotransfer functions can be used as cost-saving tools. Measures of soil nutrient status were highly variable within all mapping units and differences among farmers were much greater than the differences between soil types. Therefore, nutrient management in the study region should be based on individual field or farm recommendations rather than on soil-map based recommendations.

Notizen: Abstract. The spatial distribution of agricultural grassland in England and Wales has been assessed using a land evaluation model applied to information describing soils, climate and topography on a 5 × 5 km grid. The model calculates land suitability for grassland from assessments of trafficability/poaching risk and yield class. The spatial distribution of agricultural grassland was modelled for a 30 year climatic baseline (1941–1970) and for incremental changes in temperature and proportional changes in precipitation relative to that baseline.Model estimates for the current distribution of grassland suitability agree well with observed data of actual grassland distribution. The best suited land occurs in south west England, Wales, the Welsh borders and Cheshire with fragmented areas of well suited land in north west England and on the Pens and Humberhead levels.The climatic sensitivity analysis suggests that grassland production in England and Wales is resilient to small perturbations in mean temperature (up to +2°C) and precipitation (±10%). The effect of increasing temperature by 1°C is almost completely offset by precipitation increases of 10% resulting in little change to the distribution of grassland suitability. However, greater temperature changes (+ 4°C) have a major influence on the ability of land to support intensively managed grassland because of increased drought stress. Results indicate that a change in the climate comparable with current best estimates for the future would benefit grassland on good quality land at higher altitudes.

Notizen: Abstract. Soil productivity, the intrinsic ability of land to yield useful products, can be affected by soil erosion. While much research has been carried out on the processes, there is as yet little information on the impact of soil erosion on in situ productivity of agricultural land in the British Isles.This paper reports the results of a de-surfacing experiment on deep sandy soils in East Anglia. Grain yields of fertilized barley planted immediately after de-surfacing were at least 15 and 45% less on 15 and 25 cm de-surfaced plots than on non-desurfaced soils. There was strong evidence pointing to an acceleration of soil erosion itself on the de-surfaced plots. Both the amount of water stored in the topsoil and water use by the crop decreased with increasing severity of simulated erosion. We observed a drop in organic matter and readily available nitrogen with erosion. Nitrogen mineralization and leaching losses were also affected by simulated soil erosion.The experiment showed that sudden severe erosion may induce substantial barley production losses on deep sandy soils. The size and effect of de-surfacing depends on a number of factors such as soil depth, subsoil type, precipitation and crop type.

Notizen: Abstract. The objective of the present study was to investigate the potential of undersown catch crops to counteract soil degradation after autumn ploughing. Italian ryegrass (Lolium multiflorum Lam.) and white clover (Trifolium repens L.) were undersown in spring wheat on a loam soil in southern Norway, allowed to grow as cover crops after grain harvest and ploughed in to 20 cm depth as green manure in late October. Ryegrass prevented a collapse of the ridged plough furrow profile during winter, which occurred on grain monoculture and white-clover plots. Also, it tended to improve the water stability of aggregates, aggregate size distribution, bulk density, and pore volume in soil sampled in May. The preservation of the plough furrow profile was mainly attributed to enmeshment by an extensive system of fine roots and less to rhizosphere and microbial effects on aggregate stability. The results showed that ryegrass catch crops may give rapid structure improvements that are likely to contribute appreciably to easier seedbed preparation and less soil degradation in arable farming systems, even if the soil is ploughed in autumn.

Notizen: Abstract. Drainage hydrographs from mole-drained plots having different tillage treatments (tractor tined, gantry tined, tractor ploughed and gantry ploughed) were measured for different rain events over a growing season. In the autumn just after tillage, a large rainfall produced peaky drain flows on the tined plots but a rather flat response from the ploughed plots. In the winter, the drain response to a small rain event showed less differences in peak flows between the treatments. The recession time constant of the hydrographs was used as an index of the structural macropore development in the soil above the water table. Hydrographs from the gantry plots recessed more quickly than those on the tractor plots and those on the tined plots recessed more quickly than those on the ploughed plots. Lack of soil compaction on the gantry plots and continuous vertical fissuring created by the non-inverting tillage tines resulted in the gantry tined treatment having the fastest drainage response. In the ploughed plots compaction and smearing of the soil at the base of the plough layer restricted the rate of downward movemenl of water. The work indicates that soil management practices can play an important role in the drainage and leaching of aggregated soils.

Notizen: Abstract. Trafficked and non-trafficked (12 m gantry) crop production systems, which had been maintained on an Evesham series 60% clay soil since 1986, were used again in 1993 during the cultivation and sowing of winter wheat. After a one year set-aside break, mouldboard ploughing, tine cultivation and rotary digging were compared. Measurements were made of tillage energy, soil tilth, cone penetration resistance, biological activity and crop performance, and on specific plots, soil density, seedbed tilth and water release characteristics.Despite the one year's set-aside break, the effect of the previously applied traffic treatments remained and resulted in a smaller specific plough resistance and tillage energy on the non-trafficked soil. Tine cultivator draught however was greater on the non-trafficked compared with the trafficked plots. The specific energy required for rotary digging on non-trafficked soil was similar to that required during the ploughing of similar plots.A measure of indefinite biotic activity indicated that this was apparently greater on the non-traffficked soil, while soil density was decreased by up to 18% in these conditions compared with the trafficked land. Average cone resistance over the depth range 0 to 0.5 m was 1.51 MPa on the trafficked, compared with 1.24 MPa on the non-trafficked soil. Cone resistance also tended to be greater after tine cultivation compared with that after ploughing. Water release curves were interpreted as showing more macropores within the topsoil of the non-trafficked compared with the trafficked plots. Tine cultivation on trafficked soil had more smaller pores than mouldboard plough cultivation. Winter wheat yield was increased by 25% (from 8 to 10 t/ha) on non-trafficked compared with trafficked soil.

Notizen: Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils.

Notizen: Abstract. Data from 143 nitrogen (N) response trials on winter cereals carried out at sites across England during the period 1981–1988 were reviewed. Linear regression models for the relationship between optimum N requirements and soil mineral nitrogen (SMN) were evaluated. Multiple regression analyses and F tests were used to determine whether separate regression lines for different combinations of soil group and N Index, substituting for cropping history, were justified, and whether the additional terms used to account for SMN in the 30–60 cm and 60–90 cm depth bands significantly improved the regression model used to fit the data.The results indicated that optimum N requirement can be predicted from SMN 0–30 cm and 30–60 cm data. However, although the slope of the regression line does not change for different combinations of soil group and N Index, the intercept does. If no allowance is made for differences between sites which alter this intercept, the amount of variation in optimum N requirement accounted for by the regression models is considerably reduced. Factors which should be considered are mineralization of previous crop residues, organic manures and indigenous organic N, and the depth to which SMN is accessible by plant roots.

Notizen: Abstract. A laboratory study was designed to provide data on the decomposition of rape, sunflower and soyabean residues put in bags buried in soil. The residue bags were removed at intervals during 1 year, analysed for remaining total mass, organic and water-soluble C, water-soluble sugars, as well as for volatile acids and phenolic compounds. The decomposition dynamics of total mass, total organic and water-soluble organic C, and water-soluble sugars were reproduced satisfactorily by a double-exponential model of the first-order type.Generally, no large differences in the rate and magnitude of decomposition among the residues were observed; the greatest losses of both total mass and chemical components occurred in the first month of the study, during which the volatile acids and phenolic compounds disappeared almost completely. Of the three residues, soyabean showed the lowest loss of organic carbon, losing 66% of the original content over the course of the year compared with 73 and 75% for sunflower and rape, respectively.

Notizen: Book Review in this ArticleSoil Microbiology By R.L. Tate.

Notizen: Abstract. Because of the observed variability in soil available P (Olsen) contents, phosphorus budgets were used to predict changes in the soil P status of an intensively managed 6 ha grassland catchment in Northern Ireland. The P accumulation rate of approximately 24 kg/ha/y suggested an increase of soil available P (Olsen) of 1.0 mg P/kg/y. Soluble reactive phosphorus concentrations in drainflow measured on a daily basis for a two year period (January 1981 — December 1982) were compared with the two year period January 1990 — December 1991. The median concentration had increased by 10.0 μg P/1 in 1990/91 compared with 1981/82. This difference was only apparent in mean concentrations for the two time periods, after data associated with high flow events, which were more frequent in 1981/82, were excluded from the comparison. This rate of increase of 1.1 μg P/1/y, which was interpreted as reflecting an increase in soluble reactive phosphorus concentration in soil solution, is comparable to the increase in background soluble reactive phosphorus of 1.5 ± 0.54 μg P/1/y which was reported recently over a 17 year period from diffuse sources in the much larger (4400 km2) Northern Ireland catchment of Lough Neagh.

Notizen: Abstract. A long-term field experiment was initiated in June 1988 in a silty clay loam soil to investigate the potential of Lantana camara, an obnoxious weed, for improving structural properties and productivity of soil in rice-wheat cropping. Lantana was incorporated into the soil 10–15 days before puddling at 10, 20 and 30 t/ha (fresh weight).At the end of the sixth cropping season, Lantana additions increased the organic carbon (OC) of the 0–15 cm soil layer by 11–24%, and of water-stable aggregates (WSA, 0.50–8.0 mm diameter) by 10–21%; OC of WSA 〈0.50 mm diameter remained unaffected. About 17–25% of the applied OC was retained in the soil. The OC increase resulted in a decrease in bulk density of the plough layer (0–15 cm) by 7%, a decrease in aggregates of 2–8 mm diameter and of clods by 4% and 6%, respectively. There was an increase in water-stable aggregates and aggregate porosity, and a decrease in clod-breaking strength from 420 to 216 kPa. Soil cracking at the surface changed from wide, deep cracks in hexagonal pattern to a close-spaced network of fine cracks. Lantana additions increased 〈5mm wide cracks at the expense of 10–20 mm wide cracks; 5–10 mm wide cracks remained unchanged. Total volume of cracks decreased by 36% and surface area of cracks by 55% compared with the control plots.

Notizen: Abstract. Five soils from the South of England were incubated with additions of magnesium fertilizers; two also received magnesian limestone. After two years, the recovery of the added magnesium by 0.5 h extraction with 1 m ammonium nitrate was 75–89% for kieserite granules, 64–84% for calcined magnesite powder (〈 1 mm), but only 20–41% for calcined magnesite granules (1–3 mm) and 26–32% for ground magnesian limestone. These were all much greater than the Mg dissolved by extracting the fertilizers directly in 1 m ammonium nitrate.In calcareous soils, recovery of Mg was less from the calcined magnesite but most of this reduction was due to its particle size rather than to soil pH.The four magnesium sources are evaluated as fertilizers for agriculture. Kieserite is the most reliable means of raising low soil Mg status.

Notizen: Abstract. A qualitative model was used to assess the risk of S deficiency in cereals in Britain. A risk index was generated for each of 6301 soil data points by considering the inputs of S from atmospheric deposition, the content of soil organic matter, and factors influencing the potential leaching of sulphate, i.e. soil type, texture, pH and annual rainfall. The results show that currently 11% of the British land area is at high risk of S deficiency, and a further 22% at medium risk. The high risk areas are in south-east Scotland, the Scottish Borders, East Anglia, the Welsh Borders and south-west England. These agree well with the distribution of reported incidences of S deficiency in cereals. If the UK target for reduction in SO2 emissions by the year 2003 is met, the model predicts that the high and medium risk areas will increase to 23 and 27%, respectively. Thus, agricultural use of S-containing fertilizers is likely to increase in importance in the near future.

Notizen: Abstract. The effects of different sizes, amounts, and positions of rock fragments on soil properties and erosion were studied in experimental plots (10 treatments including bare soils and soils under natural vegetation, with 3 replicates each) installed on a hillslope.Over five events, the largest amounts of runoff were from bare soils containing abundant rock fragments, either partially embedded on the surface or incorporated in the upper part of the soil. Stoneless soils gave smaller amounts, and the smallest runoffs were measured on soils under natural vegetation. Generally, large rock fragments (cobbles) caused greater runoff than smaller fragments (coarse gravel). However, soils with appreciable amounts of coarse gravel on the surface generated considerable runoff under rainfalls of low intensity and long duration, but smaller amounts at greater rainfall intensities.Sediment loss was greater from soils with cobbles than from soils containing coarse gravel; vegetation greatly decreased sediment loss from both.In a 12-month period, the organic matter content of the soils decreased by 15.5 to 23.0%, decreasing soil aggregate stability. The organic matter content was greater in the collected sediments than in the soil.

Notizen: Abstract. The effects of rock fragments on soil temperature, soil moisture conservation, night time water vapour absorption and wheat biomass production were investigated. Under conditions of moderate water stress, water conservation was generally greater in the stony soils. Under conditions of pronounced drought the opposite occurred, with stony soils conserving less water than soils free of stones, though soils with large cobbles on the surface conserved the most water.Stony soils were generally warmer during daytime and cooler at night than soils free of rock fragments. In the warmest month (July) the diurnal amplitude reached 14.3 °C in the control soil and 24.1 °C in the stony soils. Night time absorption of water vapour in the upper 15–20 cm was less for the stony soil (17.8% cobble cover), than for the stone-free soil. Cobbles on the soil surface increased biomass production by increasing moisture conservation. After removing all the stones from the surface of 16 plots, total dry matter yield of rainfed wheat was on average 20% less than from plots with stones on the surface.

Notizen: Abstract. Economic land evaluation is a method for predicting the micro-economic value of implementing a given land-use system on a given land area. This is a more useful prediction of land performance than a purely physical evaluation, since many land-use decisions are made on the basis of economic value. Measures of economic suitability include the gross margin, net present value, internal rate of return, benefit:cost ratio, and utility functions based on these. The economic value of the in-situ resource quality of a land area may be inferred directly from land characteristics or from Land Qualities which, when less than optimum, result in decreased yields or increased costs. The economic value of geographic land characteristics may be determined by spatial analysis. Single or multi-criteria economic optimization and risk analysis can extend the economic land evaluation from a natural resource or management unit to a production or planning unit. Computerized tools may be used to assist in economic land evaluation.

Notizen: Abstract. A coarse urban compost, low in organic matter but mature, was tested for agricultural use. The response of Tewera ryegrass to this compost (applied at 12 and 48 t/ha) was evaluated in a field trial over two years. For a satisfactory yield the larger dose was necessary. This dose also gave greater values for the apparent recovery of N in both years. However, the N concentration in ryegrass was always below the sufficiency ranges proposed for N. The values of the potentially mineralizable N of the compost showed that the applied N at the greater rate of compost application was not sufficient to cover crop removal of N. In contrast, concentrations of P, S, K, Mn and Zn were within their corresponding sufficiency ranges. The dose of 48 t/ha did not increase Cu, Ni, Pb and Cd concentrations in the ryegrass.

Notizen: Abstract. The relationships between vegetation and acid properties of soils from a mangrove swamp in southeastern Nigeria were examined. Field moist soils were moderately acidic with pH ranging from 5.3 to 6.8. Air dry pH ranged from 2.9 to 4.9 indicating strong acidity; the values increased with profile depth and were related to decreasing fibrous root content. Less acidic conditions (air dry pH 4.3–4.9) were associated with the less fibrous soils under Avicennia africana and Pandanus candelabrum; more acidic conditions (air dry pH 2.9–3.8) occurred in the more fibrous Rhizophora spp. and Nypa fruticans soils. Species occurrences and levels of aluminium and sulphate in the profiles were related, suggesting that hydrogen ions, aluminium and sulphate were the main contributors to exchangeable acidity. Unless crops are known to tolerate very acidic conditions, the fibrous Rhizophora and Nypa soils should not be drained for cultivation.

Notizen: Book Reviewed in this article:Flame Spectrometry in Environmental Chemical Analysis: a practical guide By Malcolm S. Cresser.Soil compaction i n crop production Edited by B.D. Soane and C. van Ouerkerk.

Notizen: Abstract. The production of CO2 in the field and the contribution of carbon from crops to the soil were evaluated for the double crop wheat-soyabean rotation on a typical soil of the Rolling Pampa to assess the effects of two tillage systems, mouldboard ploughing and shallow discing, on the soil carbon balance. Microbial biomass and respiration under controlled conditions were also determined.No differences in soil microbial biomass contents were detected between tillage systems after two years, but the biological activity of incubated soils and the mineralized fraction of organic carbon were greater (P= 0.05) at the 0–5 cm depth in disc tillage. This suggested an increase in the labile fraction of organic matter in that layer, though the total carbon content of the soil did not vary significantly.Soil moisture was not a limiting factor at any time of the year and production of CO2 in the field was regulated by temperature (r 〉 0.89, P= 0.01). There were no differences between tillage systems in the emission of CO2 to the atmosphere, which was estimated at 11.6 t C/ha/yr. The contribution in dry matter from the crops ranged from 15.3 to 17.0 t/ha/yr, and the carbon input was approximately 7.0 t/ha/yr. Consequently, the soil lost carbon with the wheat—soyabean rotation but tillage systems did not affect carbon inputs and losses from the agrosystem.

Notizen: Abstract. Erosion was surveyed in Strath Earn, Scotland, following severe weather conditions during the first 18 days of January, 1993. A rapid field mapping system was devised to record the nature of erosion. A total of 208 fields was surveyed and 76 exhibited erosion. Most fields with erosional features were either ploughed or in autumn cereals. The most common form of erosion was ephemeral gullies along topographic hollows. This erosion was primarily associated with ploughed land whereas sheetwash and rill erosion occurred more on autumn sown land. Land use change and climatic variability, especially increasing rainfall over the last 20 years, account for the incidence of erosion. Individual erosion events rarely cause major problems for farmers, but the increasing frequency of erosion events raises important questions for sustainable land use in the arable areas of Scotland.

Notizen: Abstract. A forage model (FORYLD) was used to estimate average potential (constraint-free) yields (By) and yields under rainfed conditions (Bya) of alfalfa and wheatgrasses for the prairie region of Western Canada. Yield estimates were determined using 30-year climatic means (monthly values) and assumed available water-holding capacities (AWC) of soils ranging from 50 to 280 mm as inputs to the model. Calculations were made for 252 areas or zones known as Agroecological Resource Areas (ARAs) for the region. Estimates of By for alfalfa ranged from over 17.5 t/ha, in areas where three cuts of alfalfa were feasible if the crop were fully irrigated, to less than 10 t/ha in some northern ARAs where restricted length of the growing season limited potential to only one cut. For wheatgrasses By ranged from 15 to 17.5 t/ha in most areas where two cuts are possible. Estimates of Bya for alfalfa, based on the predominant AWC for soils in each ARA, ranged from less than 2 t/ha in the driest portion of the prairie region to more than 8 t/ha in the more humid areas. Yields of wheatgrasses were very similar to those of alfalfa in the driest zones but slightly more in some of the more humid regions. Effects of varying soil AWC on yield estimates are presented for the major soil groups of the prairies.

Notizen: Abstract. A 15-year field experiment investigated crop residue management practices, with crop residue removal, burning and incorporation as the main treatments and nitrogen levels as subtreatments. The effects of crop residue management practices on rice and wheat yield were measured for 11 years. Surface soil samples were taken to study nitrogen and phosphorus immobilization/adsorption and their release under laboratory conditions. The field experiment indicated that residue burning and residue removal resulted in greater grain yields of rice (5.57 and 5.53 t/ha, respectively) and wheat (4.12 and 4.02 t/ha, respectively) than residue incorporation (4.51 t/ha rice and 3.72 t/ha wheat). Laboratory experiments indicated that by the addition of crop residues nitrogen and phosphorus were converted to unavailable forms through immobilization and adsorption, respectively.Crop residue management practices were discontinued after 13 years and wheat and maize crops were grown in sequence. There were significantly greater yields of wheat (3.57 t/ha in 1992–93 and 3.6 t/ha in 1993–94) and of maize (2.1 t/ha in 1993) in plots where the residues had previously been incorporated than where the residues were previously either removed or burned. This is attributed to release of nitrogen and phosphorus from the incorporated residues.

Notizen: Abstract. Statistical techniques are used to test and re-interpret archival data from soil surveys of the tidal floodplain of the River Gambia. Key soil attributes include salinity, ripeness and the acid sulphate hazard. Soil taxonomic units derived by cluster analysis of all the validated data do not correspond with the intuitively-defined soil series of the original surveys. However they do correspond with practical soil mapping units, and distinguish areas of quite different geotechnical behaviour, kinds and degrees of salinity and acid sulphate hazard.

Notizen: Abstract. The effects of silt-laden Yellow River irrigation water on the properties of reclaimed dune sands were investigated at the Shapotou Research Station in Ningxia Autonomous Region, China. The practice resulted in distinct and rapid improvements in the physical and chemical properties of reclaimed desert soils. Irrigation led to the development of sandy loam topsoils, with up to 39 cm accumulating over 25 years of treatment. These topsoils had improved structure, greater soil organic matter contents and smaller bulk densities than buried desert sands. Geochemical analyses suggested river silt and sheep manure were making distinctive contributions to the improved soil fertility, with older topsoils having progressively greater concentrations of Ca, Mg, K, P, S, Fe, Mn and Zn. Soil Cr concentrations are increasing and it seems appropriate that changes in heavy metal concentrations in irrigated soils are monitored.

Notizen: Abstract. Changes in soil physical and chemical properties associated with different land uses including natural savannah were compared in Nigeria. The study was conducted on large unreplicated sites. There was a significant coarsening of texture, depletion of organic matter and nutrients and increase in bulk density under Eucalyptus camaldulensis and Mangifera indica (mango) plantations, and also under arable and fallow conditions compared with under natural vegetation. The soil conditions were slightly better under Mangifera than under Eucalyptus, and in the fallow land than the arable land and tree plantations, but the differences were mostly non-significant. The land uses studied were less efficient than the natural savannah in protecting the soil from loss of organic matter and nutrients by offtake or surface washing. The options open to Nigerian smallholder fanners are discussed in relation to sustaining soil fertility and productivity.

Notizen: Abstract. The agricultural implications of differences in soil physical properties along an Alfisol catena were evaluated. The properties studied were steady infiltration rate, saturated hydraulic conductivity (Ks), available water capacity, bulk density, field air capacity and soil texture. The catena consisted of Rhodustalfs, Haplustalfs and Tropaqualfs. A significant increase in clay content downslope was the major factor influencing the changes in associated soil physical properties. Steady state infiltration rate decreased significantly downslope. The Rhodustalfs occurring at the crest showed a steady infiltration rate of 1.91 cm/h which is optimum for surface irrigation. This decreased to 0.68 cm/h in the Haplustalfs and to 0.29 cm/h in the Tropaqualfs at the bottom of the catena; the last showing suitability for rice cultivation. Ks decreased downslope showing poor soil drainage and aeration in lower horizons of the Haplustalfs and Tropaqualfs. Available water increased downslope from 97 mm/m in the Rhodustalfs to 106 mm/m in the Haplustalfs and 122 mm/m in the Tropaqualfs. These results indicate the importance of the catena approach for soil characterization when planning agricultural projects.

Notizen: Abstract. Extraction and adsorption techniques were used to study the behaviour of Al, Fe, Mn, Co, Ni, Cu and Zn in soils from around Lake Nasser in the Eastern Desert of Egypt, to assess the potential of such areas for agricultural development and the risks of pollution of the lake. Soil metal contents were very variable, either because of particle size sorting by flowing water or through changes in redox resulting from flooding by lake water. Metal availability was low. Extraction using EDTA and oxalate suggested that mobility of copper was controlled by carbonate, whereas Co, Ni and Zn were controlled by Fe and Mn oxides. Adsorption studies confirmed the strong ability of these soils to remove Cu and Zn from solution, and suggested that Cu and Zn concentrations in solution were controlled by carbonate. Some trace metal fertilizers will probably be required for certain crops, but pollution of the lake by leaching of metals from soil is unlikely. The main process by which metals could be lost from the soil to lake water is a lowering of soil redox potential as a result of flooding by lake water.

Notizen: 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.

Notizen: 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.

Notizen: 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

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

Notizen: 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.

Notizen: 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.

Notizen: 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.

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

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

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.