Erosion rates and nutrient losses affected by composted cattle manure application in vineyard soils of NE Spain

Land preparation for mechanisation in vineyards of the Anoia–Alt Penedès region, NE Spain, has required major soil movements, which has enormous environmental implications not only due to changes in the landscape morphology but also due to soil degradation. The resulting cultivated soils are very poor in organic matter and highly susceptible to erosion, which reduces the possibilities of water intake as most of the rain is lost as runoff. In order to improve soil conditions, the application of organic wastes has been generalised in the area, not only before plantation but also every 3–4 years at rates of 30–50 Mg ha^− 1 mixed in the upper 30 cm.These organic materials are important sources of nutrients (N and P) and other elements, which could reduce further fertilisation cost. However, due to the high susceptibility to sealing of these soils, erosion rates are relatively high, so a higher nutrient concentration on the soil surface increases non-point pollution sources due to runoff.The aim of this study is to analyse the influence of applied composted cattle manure on infiltration, runoff and soil losses and on nutrients transported by runoff in vineyards of the Alt Penedès–Anoia region, NE Spain. In the two plots selected for the analysis, composted cattle manure had been applied in alternate rows 1 year previous to the study. In each plot soil surface samples (0–25 cm) were taken and compared to those of plots without manure application. The study was carried out at laboratory scale using simulated rainfall. Infiltration rates were calculated from the difference between rainfall intensity and runoff rates, and the sediment and total nitrogen and phosphorus were measured for each simulation. In addition, the influence of compost was investigated in the field under natural rainfall conditions by analysing the nutrient concentration in runoff samples collected in the field (in the same plots) after seven rainfall events, which amount different total precipitation and had different erosive character.Compost application increases infiltration rates by up to 26% and also increases the time when runoff starts. Sediment concentration in runoff was lower in treated (13.4 on average mg L^− 1) than in untreated soils (ranging from 16.8 to 23.4 mg L^− 1). However, the higher nutrient concentration in soils produces a higher mobilisation of N (7–17 mg L^− 1 in untreated soils and 20–26 mg L^− 1 in treated soils) and P (6–7 mg L^− 1 in untreated soils and 13–19 mg L^− 1 in treated soils). A major part of the P mobilised was attached to soil particles (about 90% on average) and only 10% was dissolved. Under natural conditions, higher nutrient concentrations were always recorded in treated vs. untreated soils in both plots, and the total amount of N and P mobilised by runoff was higher in treated soils, although without significant differences. Nutrient concentrations in runoff depend on rainfall erosivity but the average value in treated soils was twice that in untreated soils for both plots.     

Hydrological pathway and source area of nutrient losses identified by a multi-scale monitoring in an agricultural catchment

The objectives of the study were to identify principal hydrological pathways and source areas of N and P losses by multi-scale monitoring and to estimate total nutrient losses from the catchment. An agricultural catchment with rain-fed agriculture and irrigated paddy fields in subtropical China was monitored with regularly sampling, together with intensive sampling during and after rain storms. Regular weekly sampling showed that the N concentrations in the overland flows from the upland and paddy fields were higher than those from the streams, but lower than those in the subsurface waters. The N concentration, on average, was 10.0 mg L^− 1 in the well and 1.7 mg L^− 1 in the spring water, the former was 10.2 times as high as that in the stream waters (1.0–1.5 mg L^− 1). Nitrogen and P in the overland flows originated dominantly in particulate forms from the uplands (over 70%) and in dissolved forms from the paddy fields. Inorganic N and P dominated in the streams and subsurface waters. The intensive sampling allowed us to establish flow-nutrient concentration relationships and to extrapolate nutrient losses during rainstorms without regular sampling. The extrapolation increased the estimated nutrient losses by about 30% to 50%. The average total nutrient losses within three water years were estimated as 21 kg N ha^− 1 yr^− 1 and 1 kg P ha^− 1 yr^− 1, accounting for 9.5% and 1.4% of chemical N and P fertilizers applied to the catchment after subtracting the nutrient inputs with irrigation and rainfall. The estimation showed that paddy fields were as important as the uplands in terms of nutrient losses. These results suggest that control of soil erosion and excessive irrigation could be effective to reduce nutrient export through overland flow and subsurface flow.     

How does the first year tilling a long-term no-tillage field impact soluble nutrient losses in runoff?

Conservation tillage practices are commonly used to reduce erosion; however, in fields that have been in no-tillage (NT) for long periods, compaction from traffic can restrict infiltration. Rotational tillage (RT) is a common practice that producers use in the central corn-belt of the United States, and could potentially reduce soluble nutrient loads to surface waters. The objectives of this study were to determine the first year impacts of converting from long-term NT to (RT) on N and P losses through runoff. Plots (2 m × 1 m) were constructed in two fields that had been in NT corn–soybean rotation for the previous 15 years. One field remained in NT management, while RT was initiated prior to planting corn in the other field using a soil finisher. Variable-intensity rainfall simulations occurred before and after fertilization with urea (224 kg N ha⁻¹) and triple superphosphate (112 kg P ha⁻¹). Rainfall was simulated at (1) 50 mm h⁻¹ for 50 min; (2) 75 mm h⁻¹ for 15 min; (3) 25 mm h⁻¹ for 15 min; (4) 100 mm h⁻¹ for 15 min. Runoff volumes and nutrient (NH₄-N, NO₃-N and dissolved P [DP]) concentrations were greater from the NT field than the RT field before and after fertilization.Dissolved P concentrations in runoff prior to fertilization were greater during the 50 mm h⁻¹ rainfall period (0.09 mg L⁻¹) compared to the other periods (0.03 mg L⁻¹). Nutrient concentrations increased by 10–100-fold when comparing samples taken after fertilization to those taken prior to fertilization. Nutrient loads were greater prior to and after fertilization from the NT treatment. Prior to fertilization, NT resulted in 83 g ha⁻¹ greater NH₄-N and 32.4 g ha⁻¹ greater dissolved P losses than RT treatment. After fertilization, NT was observed to lose 5.3 kg ha⁻¹ more NH₄-N, 1.3 kg ha⁻¹ more NO₃-N, and 2.4 kg ha⁻¹ more dissolved P than RT. It is typically difficult to manage land to minimize P and N losses simultaneously; however, in the short term, tillage following long-term NT resulted in lowering the risk of transport of soluble N and P to surface water.     

Modelling of snowmelt erosion and sediment yield in a small low-mountain catchment in Germany

Temporal variability and spatial heterogeneity of surface runoff generation triggers the dynamics of source areas of sediment and sediment-associated nutrient transport. Reliable modelling of hydrological special situations i.e. snowmelt is of high importance for the quality of erosion and sediment yield modelling. Data from the research catchment Schäfertal demonstrate the individuality of snowmelt events in terms of runoff coefficient and delivery ratio. This 1.44 km² low mountain catchment is characterised by a high portion of arable land with a winter grain/winter rape crop rotation. The integrated winter erosion and nutrient load model (IWAN) considers these dynamic aspects by coupling a hydrological model with a sediment load model. Cell size of this raster-based approach is 10 × 10 m². Additionally, snowmelt rill erosion is simulated with a newly developed physically based model that is firstly applied on a catchment scale. A sensitivity analysis of this model system component demonstrates the plausibility of the model approach and the overall robustness of the model system IWAN. The results of the long-term hydrological modelling from 1991 to 2003 are reliable and form the basis for the simulation of six snowmelt events which were observed in the Schäfertal catchment. The estimated total runoff volumes for these events match the observations well. The modelled overland runoff coefficients vary from 0.001 to 0.72. The mean values of cell erosion, which were modelled with one set of parameters for all six events range from 0.0006 to 0.96 t ha^− 1. The total modelled erosion for the events with unfrozen soil and low amount of surface runoff is of a factor 50 below those with partly frozen soil. In addition to these distinctions, the major differences are caused by flow accumulation in shallow depressions in variable parts of the catchment. However, the validation of these results on the single event scale is restricted due to limited spatial data. Total simulated sediment yield at the catchment outlet was as high as 13.84 t which underestimates the observed values, with the exception of one event. Oversimplification of the modelled channel processes may be a reason. The temporal variability and spatial heterogeneity of the surface roughness parameter, which was identified to be sensitive, also causes uncertainty in the parameter estimation. Despite these findings, the model system IWAN was applied successfully on the catchment scale and the simulated results are reliable.     

Management of a previously eroded tropical Alfisol with herbaceous legumes: Soil loss and physical properties under mound tillage

A study was carried out on a previously eroded Oxic Paleustalf in Ibadan, southwestern Nigeria to determine the extent of soil degradation under mound tillage with some herbaceous legumes and residue management methods. A series of factorial experiments was carried out on 12 existing runoff plots. The study commenced in 1996 after a 5-year natural fallow. Mound tillage was introduced in 1997 till 1999. The legumes – Vigna unguiculata (cowpea), Mucuna pruriens and Pueraria phaseoloides – were intercropped with maize in 1996 and 1998 while yam was planted alone in 1997 and 1999. This paper covers 1997–1999. At the end of each year, residues were either burned or mulched on respective plots. Soil loss, runoff, variations in mound height, bulk density, soil water retention and sorptivity were measured. Cumulative runoff was similar among interactions of legume and residue management in 1997 (57–151 mm) and 1999 (206–397 mm). However, in 1998, cumulative runoff of 95 mm observed for Mucuna-burned residue was significantly greater than the 46 mm observed for cowpea-burned residue and the 39–51 mm observed for mulched residues of cowpea, Mucuna and Pueraria. Cumulative soil loss of 7.6 Mg ha⁻¹ observed for Mucuna-burned residue in 1997 was significantly greater than those for Pueraria-mulched (0.9 Mg ha⁻¹) and Mucuna-mulched (1.4 Mg ha⁻¹) residues whereas in 1999 it was similar to soil loss from cowpea treatments and Pueraria-burned residue (2.3–5.3 Mg ha⁻¹). There were no significant differences in soil loss in 1998 (1–3.2 Mg ha⁻¹) whereas Mucuna-burned residue had a greater soil loss (28.6 Mg ha⁻¹) than mulched cowpea (6.9 Mg ha⁻¹) and Pueraria (5.4 Mg ha⁻¹). Mound heights (23 cm average) decreased non-linearly with cumulative rainfall. A cumulative rainfall of 500 mm removed 0.3–2.3 cm of soil from mounds in 1997, 3.5–6.9 cm in 1998 and 2.3–4.6 cm in 1999, indicating that (detached but less transported) soil from mounds was far higher than observed soil loss in each year. Soil water retention was improved at potentials ranging from −1 to −1500 kPa by Mucuna-mulched residue compared to the various burned-residue treatments. Also, mound sorptivity at −1 cm water head (14.3 cm h^−1/2) was higher than furrow sorptivity (8.5 cm h^−1/2), indicating differences in hydraulic characteristics between mound and furrow. Pueraria-mulched residues for mounds had the highest sorptivity of 17.24 cm h^−1/2, whereas the least value of 6.96 cm h^−1/2 was observed in furrow of Mucuna-burned residue. Pueraria phas eoloides was considered the best option for soil conservation on the previously eroded soil, cultivated with mound tillage.     

Soil erosion and deposition rates in a cultivated catchment area in central Greece, estimated using the Cs technique

The spatial variation of soil erosion and deposition rates was studied in a small catchment cultivated by rainfed agriculture, in the Mouriki area, Viotia Greece, using the ¹³⁷Cs technique. A 25 m grid was established parallel to the slope and the ¹³⁷Cs inventories were defined for the grid points. After establishing the local reference inventory, the soil erosion and deposition rates were estimated using the ¹³⁷Cs residuals for individual points on the grid in conjunction with the four conversion (calibration) models described by Walling and He (2001) [Models for converting ¹³⁷Cs measurements to estimates of soils redistribution rates on cultivated and uncultivated soils]. The conversion models were validated by means of sensitivity analysis and using local experimental data. The resulting estimates of soil redistribution rates were interpolated by means of kriging, using Surfer Golden software. The magnitude of the soil erosion rates depend on many factors, including the location of the sampling point, the local slope, and the soil properties. The mass balance model 2 (MBM2) and mass balance model incorporating soil movement by tillage (MBM3) conversion models predict soil redistribution rates of the same order of magnitude as the experimental data and are able to take account of Chernobyl fallout. Predicted soil erosion rates for catchment grid varied from 6.71 to 85.55 t ha⁻¹ per year using MBM2 and from 3.54 to 95.78 t ha⁻¹ per year using MBM3. Deposition rates varied from 1.23 to 168.19 t ha⁻¹ per year using MBM2 and from 3.24 to 189.18 t ha⁻¹ per year using MBM3. High correlation was apparent between erosion/deposition rates (MBM2) and soil P (P<0.001), soil K (P<0.001), soil organic matter % (P<0.05), point slope (P<0.05), clay % (P=0.053) and altitude (P=0.057). The total soil losses from the catchment have been estimated at 18.34 t ha⁻¹ per year using MBM2 and 22.12 t ha⁻¹ per year using MBM3.     

Tillage and cropping sequence impacts on nitrogen cycling in dryland farming in eastern Montana, USA

Information on N cycling in dryland crops and soils as influenced by long-term tillage and cropping sequence is needed to quantify soil N sequestration, mineralization, and N balance to reduce N fertilization rate and N losses through soil processes. The 21-yr effects of the combinations of tillage and cropping sequences was evaluated on dryland crop grain and biomass (stems + leaves) N, soil surface residue N, soil N fractions, and N balance at the 0–20 cm depth in Dooley sandy loam (fine-loamy, mixed, frigid, Typic Argiboroll) in eastern Montana, USA. Treatments were no-tilled continuous spring wheat (Triticum aestivum L.) (NTCW), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat–barley (Hordeum vulgare L.) (1984–1999) followed by spring wheat–pea (Pisum sativum L.) (2000–2004) (FSTW-B/P), and spring-tilled spring wheat–fallow (STW-F). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH₄-N, and NO₃-N. Annualized crop grain and biomass N varied with treatments and years and mean grain and biomass N from 1984 to 2004 were 14.3–21.2 kg N ha⁻¹ greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. Soil surface residue N was 9.1–15.2 kg N ha⁻¹ greater in other treatments than in STW-F in 2004. The STN at 0–20 cm was 0.39–0.96 Mg N ha⁻¹, PON 0.10–0.30 Mg N ha⁻¹, and PNM 4.6–9.4 kg N ha⁻¹ greater in other treatments than in STW-F. At 0–5 cm, STN, PON, and MBN were greater in STCW than in FSTW-B/P and STW-F. At 5–20 cm, STN and PON were greater in NTCW and STCW than in STW-F, PNM and MBN were greater in STCW than in NTCW and STW-F, and NO₃-N was greater in FSTW-B/P than in NTCW and FSTCW. Estimated N loss through leaching, volatilization, or denitrification at 0–20 cm depth increased with increasing tillage frequency or greater with fallow than with continuous cropping and ranged from 9 kg N ha⁻¹ yr⁻¹ in NTCW to 46 kg N ha⁻¹ yr⁻¹ in STW-F. Long-term no-till or spring till with continuous cropping increased dryland crop grain and biomass N, soil surface residue N, N storage, and potential N mineralization, and reduced N loss compared with the conventional system, such as STW-F, at the surface 20 cm layer. Greater tillage frequency, followed by pea inclusion in the last 5 out of 21 yr in FSTW-B/P, however, increased N availability at the subsurface layer in 2004.     

Ex-post evaluation of erosion control measures in southern Mali

As part of an impact study of a soil and water conservation (SWC) project in southern Mali, the effect of erosion control measures on soil erosion was evaluated. In one village, a baseline situation from 1988 was compared with the situation in 2003, after farmers had installed stone rows, live fences and grass strips, and had started cultivating across to the slope. This comparison showed a spectacular decrease in gully volume in cultivated fields of 87%, from 58 to 8 m³ ha⁻¹. Estimated annual soil loss decreased with 77% from 42 to 10 t ha⁻¹ year⁻¹. However, baseline data on erosion gullies were not available for other villages. In the absence of baseline data, a simple ‘with–without’ comparison does not allow a correct evaluation because farmers install erosion control measures especially in fields with more erosion. Two alternative methods were used: a reconstructed baseline and a virtual time series. Using the reconstructed baseline, looking not only at active gullies but also at (partly) reclaimed gullies, we concluded that line interventions, gully interventions, and a combination of both, reduced the proportion of active gullies by 48%, 47% and 70%, respectively. Using a virtual time series, comparing erosion in fields with erosion control measures installed in different years, we concluded that erosion gradually decreased by 50% during the 3 years after installation of erosion control measures. In a separate study, we found a positive effect of gully interventions and sowing across to the slope in reducing sheet erosion. A reduction of the slope of the sowing direction by 1% reduced the cover of runoff deposit of coarse sand with 8%. Although a documented baseline is preferred, both a reconstructed baseline and a virtual time series are useful tools and make ex-post evaluations more relevant than a simple with–without comparison.     

Contour furrows for in situ soil and water conservation, Tigray, Northern Ethiopia

In Tigray (Northern Ethiopia), soil moisture has been identified as the most limiting factor in agricultural production; on the other hand, loss of rain water through runoff as well as the induced soil loss has been determined as a critical problem in the region in the last two to three decades. To alleviate the above paradox, the government has mobilized communities and resources for the construction of physical soil and water conservation structures (stone bunds, terraces) in almost all land uses. However, yield improvement was mainly concentrated within the vicinity of the structures and runoff continued to overtop the structures, as no measures for in situ soil conservation were taken. The terwah system, consisting of traditional ploughing followed by making every 1.5–2 m contour furrows, and permanent raised beds with contour furrows at 60–70 cm interval treatments, were considered and evaluated as practices that could increase the efficiency of in situ water utilization and soil conservation. An experiment was started in Gum Selasa, which is one of the drought prone areas in Tigray, whereby runoff volume and sediment load were measured after every rain event. Permanent raised beds with contour furrows at 60–70 cm interval significantly (P < 0.05) reduced runoff volume, runoff coefficient and soil loss as compared to traditional ploughing: 255, 381 and 653 m³ ha⁻¹ runoff was recorded from permanent bed, terwah and traditional ploughing, respectively during the whole cropping season. The above runoff induced 4.7 t ha⁻¹ soil loss from permanent bed, 7.6 t ha⁻¹ from terwah and 19.5 t ha⁻¹ from traditional ploughing. Overall, contour furrows and permanent raised beds can be part of the ongoing intensification process which includes physical soil and water conservation, slope reforestation, irrigation development and agro forestry in crop lands. Moreover, the use of permanent raised beds if combined with crop mulching and crop diversification is an important component for the development of sustainable conservation agriculture practices in the region.     

The utility of process-based models for simulating N2O emissions from soils: A case study based on Costa Rican coffee plantations

Soil moisture and gaseous N-flux (N₂O, N₂) dynamics in Costa Rican coffee plantations were successively simulated using a mechanistic model (PASTIS) and two process-based models (NGAS and NOE). Two fertilized (250 kg N ha⁻¹ y⁻¹) coffee plantations were considered, namely a monoculture and a system shaded by the N₂ fixing legume species Inga densiflora. In situ N₂O fluxes were previously measured in these plantations. NGAS and NOE used specific microbial activities for the soils. To parameterize NGAS, we estimated N mineralization via in situ incubations and the contribution of heterotrophic soil respiration to total soil respiration. Potential denitrification rates and the proportion of denitrified N emitted as N₂O were measured in the laboratory to define the values of NOE parameters, as well as nitrification rates and related N₂O production rates for parameterizing both models. Soil moisture and both NGAS and NOE N₂O fluxes were best modelled on an hourly time step. Soil moisture dynamics were satisfactorily simulated by PASTIS. Simulated N₂O fluxes by both NGAS and NOE (3.2 and 2.1 kg N ha⁻¹ y⁻¹ for NGAS; 7.1 and 3.7 kg N ha⁻¹ y⁻¹ for NOE, for the monoculture and shaded plantations respectively) were within a factor of about 2 of the observed annual fluxes (4.3 and 5.8 kg N ha⁻¹ y⁻¹, for the monoculture and shaded plantations respectively). Statistical indicators of association and coincidence between simulated and measured values were satisfactory for both models. Nevertheless, the two models differed greatly in describing the nitrification and denitrification processes. Some of the algorithms in the model NGAS were apparently not applicable to these tropical acidic Andosols. Therefore, more detailed information about microbial processes in different agroecosystems would be needed, notably if process-oriented models were to be used for testing strategies for mitigating N₂O emissions.     

Nutrient losses from rain‐fed bench terraced cultivation systems in high rainfall areas of the mid‐hills of Nepal

Between the elevations of 1000 and 2000 m in the mid‐hills of Nepal, over 12 million people subsist on land‐holdings of less than 0·5 ha. These farmers have limited access to commercial inputs such as fertilisers and are reliant on organic manures for soil fertility maintenance. Participatory research was conducted with farmers on bari land (upper slope rain‐fed crop terraces) in the hill community of Landruk (bench terraces 0–5° slope, 3000–3500 mm annual rainfall, which aimed to develop soil and water management interventions that controlled erosion without resulting in high leaching, and so were effective in minimising total nutrient losses. Interventions tested were the control of water movement through diversion of run‐on and planting fodder grasses on terrace risers on bench terraces. The interventions were effective in reducing soil loss from the bari land in comparison with existing farmer practices, but no effect was observed on nutrient losses in solution form through runoff and leaching. Losses of NO₃‐N in leachate ranged from 17·3 to 99·7 kg ha⁻¹ yr⁻¹, but only 0·7 to 5·6 kg ha⁻¹ yr⁻¹ in runoff. The overall nutrient balance suggests that the system is not sustainable. Fertility is heavily dependent on livestock inputs and if the current trends of declining livestock numbers due to labour constraints continue, further losses in productivity can be expected. However, farmers are interested in interventions that tie ecosystem services with productivity enhancement and farmers' priorities should be used as entry points for promoting interventions that are system compatible and harness niche opportunities. Copyright © 2007 John Wiley & Sons, Ltd.     

西班牙东南部旱作橄榄树果园水土保持措施: 植物带对土壤水分的动态影响

Sloping and mountainous olive production systems are widespread, occupying large parts of the Mediterranean landscape prone to water erosion. Soil erosion, runoff, and soil water content patterns over a three-year period were monitored in erosion plots on a mountainside with rainfed olive (Olea europaea cv. Picual) trees under: 1) non-tillage with barley strips of 4 m width (BS); 2) non-tillage with native vegetation strips of 4 m width (NVS); and 3) non-tillage without plant strips (NT). The erosion plots, located in Lanjaron (Granada, south-eastern Spain), on a 30% slope, were 192 m² in area. For assessing soil water dynamics in real-time and near-continuous soil water content measurements, multisensor capacitance probes were installed in the middle of plant strips and beneath the olive tree at five soil depths (10, 20, 30, 50, and 100 cm). The highest erosion and runoff rates were measured under NT, with a mean of 17.3 Mg ha^-1 year^-1 and 140.0 mm year^-1, respectively, over the entire study period. The BS and NVS with respect to the NT reduced erosion by 71% and 59% and runoff by 95% and 94%, respectively. In general, greater available soil water content was found under BS than NVS and NT, especially beneath the olive tree canopies. These results supported the recommendation of non-tillage with barley strips in order to reduce erosion and to preserve soil water for trees in traditional mountainous olive-producing areas, where orchards cover vast tracts of land.     

Characterization of soil profiles in a landscape affected by long-term tillage

Soil movement by tillage redistributes soil within the profile and throughout the landscape, resulting in soil removal from convex slope positions and soil accumulation in concave slope positions. Previous investigations of the spatial variability in surface soil properties and crop yield in a glacial till landscape in west central Minnesota indicated that wheat (Triticum aestivum) yields were decreased in upper hillslope positions affected by high soil erosion loss. In the present study, soil cores were collected and characterized to indicate the effects of long-term intensive tillage on soil properties as a function of depth and tillage erosion. This study provides quantitative measures of the chemical and physical properties of soil profiles in a landscape subject to prolonged tillage erosion, and compares the properties of soil profiles in areas of differing rates of tillage erosion and an uncultivated hillslope. These comparisons emphasize the influence of soil translocation within the landscape by tillage on soil profile characteristics. Soil profiles in areas subject to soil loss by tillage erosion >20 Mg ha⁻¹ year⁻¹ were characterized by truncated profiles, a shallow depth to the C horizon (mean upper boundary 75 cm from the soil surface), a calcic subsoil and a tilled layer containing 19 g kg⁻¹ of inorganic carbon. In contrast, profiles in areas of soil accumulation by tillage >10 Mg ha⁻¹ year⁻¹ exhibited thick sola with low inorganic carbon content (mean 3 g kg⁻¹) and a large depth to the C horizon (usually >1.5 m below the soil surface). When compared to areas of soil accumulation, organic carbon, total nitrogen and Olsen-extractable phosphorus contents measured lower, whereas inorganic carbon content, pH and soil strength measured higher throughout the profile in eroded landscape positions because of the reduced soil organic matter content and the influence of calcic subsoil material. The mean surface soil organic carbon and total nitrogen contents in cultivated areas (regardless of erosion status) were less than half that measured in an uncultivated area, indicating that intensive tillage and cropping has significantly depleted the surface soil organic matter in this landscape. Prolonged intensive tillage and cropping at this site has effectively removed at least 20 cm of soil from the upper hillslope positions.     

Planting methods and nitrogen effects on crop yield and soil quality under direct seeded rice in the Indo-Gangetic plains of eastern India

A field trial was conducted during the kharif (rainy) seasons of 2002 and 2003 at the Research Farm, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, India. The trial was carried out to study the effect of planting methods, sources and levels of nitrogen on soil properties, yield and NPK uptake by rice (Oryza sativa L.) under direct seeded condition. Planting methods significantly influenced the physical, chemical and biological properties of soil. Bulk density (1.385 g cm⁻³), organic carbon (0.43%) and soil moisture content (15.46%) were higher in zero till seeding plots than rotavator and conventional seeding. However, infiltration rate, soil temperature, pH and electrical conductivity showed a declining trend under this treatment and were found maximum (11.54 mm h⁻¹, 36.21 °C at 55 DAS, 30.65 °C at harvest, 7.59 and 0.47 ds m⁻¹) with conventional seeding. The maximum population of bacteria (25.60 × 10⁵), fungi (14.26 × 10⁴) and azotobactor (10.19 × 10³) were found in the plot with zero till seeding while in case of actinomycetes the highest population (25.61 × 10⁵) was found in conventional seeding. Nitrogen sources as well as levels failed to bring about any significant change in the soil properties. The highest grain (3825 kg ha⁻¹) and straw yields (5446 kg ha⁻¹) and N, P, K uptake were recorded in conventional seeding and were found significantly superior to zero till seeding (3144 kg ha⁻¹) but it remained at par with rotavator seeding (3585 kg ha⁻¹). Among the nitrogen sources, neem (Azadirachta indica) coated urea produced significantly higher grain (3761 kg ha⁻¹) and straw yields (5396 kg ha⁻¹) with greater NPK uptake than prilled urea and prilled urea + spent mentha. (The distillation waste of mint (Mentha arvensis) herbage is known as spent mentha.) Application of 150 kg N ha⁻¹ produced maximum grain (3828 kg ha⁻¹) and straw yields (5460 kg ha⁻¹) although it remained at par with 100 kg N ha⁻¹ (3738 and 5393 kg ha⁻¹).     

The WEELS model: methods, results and limitations

Within the European Union (EU)-funded Project ‘Wind Erosion on European Light Soils’ (WEELS), a model was designed and implemented with the aim of predicting the long-term spatial distribution of wind erosion risks in terms of erosion hours and wind-induced soil loss. In order to ensure wide applicability, the model structure consists of a modular combination of different approaches and algorithms, running on available or easily collected topographic and climatological data input. Whereas the ‘WIND’, ‘WIND EROSIVITY’ and ‘SOIL MOISTURE’ modules combine factors that contribute to the temporal variations of climatic erosivity, the ‘SOIL ERODIBILITY’, ‘SURFACE ROUGHNESS’ and ‘LAND USE’ modules predict the temporal soil and vegetation cover variables that control soil erodibility. Preliminary simulations over a 29-year period for the Barnham site (UK) (1970–1998) and a 13-year period for the Grönheim site (Germany) (1981–1993) generally resulted in a higher erosion risk for the English test site, where the total mean soil loss was estimated at 1.56 t ha⁻¹ year⁻¹ and mean maximum soil loss at about 15.5 t ha⁻¹ year⁻¹. The highest rates exceeded 3 t ha⁻¹ in March, September and November. On the northern German test site, the total mean soil loss was 0.43 t ha⁻¹ year⁻¹. The highest erosion rates were predicted in April when they can exceed 2.5 t ha⁻¹. The total mean maximum soil loss at this site of about 10.0 t ha⁻¹ year⁻¹ corresponds to a loss of about 0.65 mm. Predictions based on a land use scenario for the German site revealed that the erosion risk could be reduced significantly by changing land use strategies.     

Land-use impacts on surface runoff and soil detachment within agricultural sloping lands in Northern Vietnam

Two consecutive years of investigation on soil surface features, surface runoff and soil detachment within 1-m² microplots on 40% slope highlighted the effects of land-use change, vegetation cover and biological activity on the water pathways in Northern Vietnam. Three replicate plots were set up on each of five land-uses: cassava (CAS), grass fodder of Bracharia ruziziensis (BRA), a 3-year old fallow (FAL), tree stands of Acacia mangium and Venicia montana (FOR), and a fallow with regrowth of Eucalyptus regularly cut (EUC). The second year, two of the microplots under FAL and EUC were treated with herbicide (FALh, EUCh), one of them was burnt (FALh+b, EUCh+b). The highest yearly surface runoff coefficient of 16%, and soil detachment rate of 700 g m^− 2 yr^− 1 in average with a maximum of 1305 g m^− 2 yr^− 1 have been recorded under CAS. On FALh and FALh+b, runoff ratios were 8.7 and 13.5%, respectively and detachment rates were 86 and 389 g m^− 2. On FAL and BRA the yearly runoff ratio varied from 5.9 to 9.8% but the detachment rate was limited at 24 to 35 g m^− 2. FOR and EUC annual runoff was ≤ 3.1% and annual soil detachment ≤ 71 g m^− 2. These values were very low compared to the values reported on steep slopes in Laos within similar climate and vegetation cover.The runoff and detachment rates underlined the importance of rainfall intensities, soil physical properties, soil surface features, soil vegetation cover and biological activity. The annual surface runoff was highly correlated to the soil surface crusting. CAS and BRA plots were prone to crusting especially after weeding at the onset of the rainy season, when the soil surface was still uncovered. Soil bioturbation (earthworm casting activity) was the second factor that explains local variation of surface runoff and soil detachment. The continuous production of earthworms casts on soil surface, especially on FOR and EUC microplots, induced a marked surface roughness and reduced the surface runoff. The production of casts was very limited in FAL and completely absent in CAS microplots. So it is evident that our results confirm the deleterious effects of cassava on soil and water conservation.     

Effect of organic and inorganic nutrient sources on soil mineral nitrogen and maize yields in central highlands of Kenya

High population pressure in the central highlands of Kenya has led to continuous cultivation of land with minimal additional inputs leading to soil nutrient depletion. Research work has reported positive results from use of manure and biomass from Tithonia, Calliandra, Leucaena, Mucuna and Crotolaria for soil fertility replenishment. An experimental field was set up in Chuka Division to test different soil nutrient replenishment treatments. The experimental design was randomised complete block with 14 treatments replicated three times. At the beginning and end of the experiment, soil was sampled at 0–15 cm depth and analysed for pH, Ca, Mg, K, C, N and P. End of the 2000/2001 short rains (SR) season and 2001 long rains (LR) season, soil samples were taken at 0–30, 30–100 and 100–150 cm for nitrate and ammonium analysis. All the treatments received an equivalent of 60 kg N ha⁻¹, except herbaceous legume treatments, where N was determined by the amount of the biomass harvested and incorporated in soil and control treatment received no inputs. Results indicate soil fertility increased slightly in all treatments (except control) over the 2-year study period. Average maize grain yield across the treatments was 1.1, 5.4, 3.5 and 4.0 Mg ha⁻¹ during the 2000 LR, 2000/2001 SR, 2001 LR and 2001/2002 SR, respectively. The reduced yield in 2000 LR and 2001 LR are attributed to poor rainfall distribution during the two seasons. On average, Tithonia with half recommended rate of inorganic fertilizer recorded the highest (4.8 Mg ha⁻¹) maize yield followed by sole Tithonia (4.7 Mg ha⁻¹). Highest average concentration (144.8 and 115.5 kg N ha⁻¹) of mineral N was recorded at the 30–100 cm soil depth at the end of both 2000/2001 SR and LR, respectively. The lowest average concentration (67.1 kg N ha⁻¹) was recorded in the 100–150 cm soil depth in both seasons, while during the 2001 LR, the 0–30 cm soil depth recorded the lowest concentration (52.3 kg N ha⁻¹). The residual mineral N in the 100–150 cm soil depth doubled at the end of the LR 2001 compared to what was present and the end of the SR 2000/2001 season in all treatments. This shows that there is substantial amount of mineral N that is being leached below the rooting zone of maize in this region.     

Slope sediment yield in arid lowland continuous permafrost environments, Canadian Arctic Archipelago

Surface wash erosion was measured at runoff plots on low to moderate slopes in clayey and sandy silts underlain by continuous permafrost on the Fosheim Peninsula, Ellesmere Island. Due to snow redistribution in winter, total precipitation on the plots varied from 34 to 150 mm, with corresponding surface runoff values of 0 to 102 mm. Where runoff occurred, at least 80% of it was derived from snowmelt. Suspended sediment removal was <75 g m⁻² a⁻¹ at relatively well-vegetated sites but averaged more than 1200 g m⁻² a⁻¹ at a plot where the vegetation had been removed by landsliding. Niveo-aeolian deposition was greater than suspended sediment removal at some plots, indicating net accumulation. Solute removal ranged up to 80 g m⁻² a⁻¹ and exceeded clastic sediment transport at one vegetated site. Elevated rates of erosion at the sites of detachment slides that pre-date 1950 demonstrated that terrain disturbance in permafrost environments can affect slopewash processes for at least several decades.Plot data (precipitation, vegetation and surface grain-size) from the Fosheim Peninsula and Banks Island were used to develop a statistical model of suspended sediment removal by surface wash on undisturbed slopes. For any given grain-size, the model predicts a rise in erosion from zero precipitation (because of an absence of runoff) to a peak at about 50 mm, a decline as precipitation increases to 300 mm and a further increase in erosion beyond this inflection point. This non-linear response is due to the complex interaction of moisture (primarily snow) and vegetation cover. Erosion at any given precipitation value varies through three orders of magnitude depending on surface grain-size. The maximum erosion predicted is 1 kg m⁻² a⁻¹ for a runoff plot with 1100 mm of precipitation, a corresponding vegetation cover of 77% and a median surface grain-size of 7 φ.     

An Economic Analysis of the Potential for Precision Farming in UK Cereal Production

The results from alternative spatial nitrogen application studies are analysed in economic terms and compared to the costs of precision farming hardware, software and other services for cereal crops in the UK. At current prices, the benefits of variable rate application of nitrogen exceed the returns from a uniform application by an average of £22 ha⁻¹ The cost of the precision farming systems range from £5 to £18 ha⁻¹ depending upon the system chosen for an area of 250 ha. The benefits outweigh the associated costs for cereal farms in excess of 80 ha for the lowest price system to 200–300 ha for the more sophisticated systems. The scale of benefits obtained depends upon the magnitude of the response to the treatment and the proportion of the field that will respond. To be cost effective, a farmed area of 250 ha of cereals, where 30% of the area will respond to variable treatment, requires an increase in crop yield in the responsive areas of between 0·25 and 1.00 t ha⁻¹ (at £65 t⁻¹) for the basic and most expensive precision farming systems, respectively.     

Soil structure and organic carbon relationships following 10 years of wheat straw management in no-till

Crop residue retention is important for sequestering soil organic carbon (SOC), controlling soil erosion, and improving soil quality. Magnitude of residue management impacts on soil structural properties and SOC sequestration is, however, site specific. This study assessed long-term (10 year) impacts of three levels (0, 8, and 16 Mg ha⁻¹ on a dry matter basis) of wheat (Triticum aestivum L.) straw applied annually on SOC concentration and physical properties of the bulk soil and individual 5- to 8-mm aggregates for the 0- to 50-cm soil depth under no-till (NT) on a Crosby silt loam (fine, mixed, active, mesic Aeric Epiaqualfs) in central Ohio. This study also quantified relationships between soil properties and straw-induced changes in SOC concentration. Changes in soil properties due to straw mulching were mostly confined to the upper 5 cm of the soil. Mulching increased SOC concentration, but it did not significantly change cone index (CI) and shear strength (SHEAR). Within the upper 0–5-cm soil depth, mulching decreased bulk density (ρ_b) by 40–50%, aggregate density (ρ_agg) by 30–40%, and particle density (ρ_s) by 10–15%, and increased tensile strength (TS) of aggregates by up to 14 times as compared to unmulched soil. At the same depth, soil with mulch retained >30% more water than soil without mulch from 0 to −1500 kPa potentials. The SOC amount was 16.0 Mg ha⁻¹ under no straw, 25.3 Mg ha⁻¹ under 8 Mg ha⁻¹ straw, and 33.5 Mg ha⁻¹ under 16 Mg ha⁻¹ straw in the 0- to 10-cm depth. Below 10 cm, differences in SOC pool between mulched and unmulched soil were not significant. Overall, SOC from 0- to 50-cm depth was 82.5 Mg ha⁻¹ for unmulched soil, 94.1 Mg ha⁻¹ for 8 Mg ha⁻¹ mulch, and 104.9 Mg ha⁻¹ for 16 Mg ha⁻¹. About 33% of C added with straw over the 10-year period was sequestered in soil. This means that 2/3 of the wheat straw applied was not converted to SOC and most probably was lost as emissions of CO₂ and CH₄. The annual rate of total C accrual was 1.2 Mg ha⁻¹ in soil mulched with 8 Mg ha⁻¹ and 2.2 Mg ha⁻¹ in soil mulched with 16 Mg ha⁻¹ of straw in the 0- to 50-cm depth. The percentage of macroaggregates (>5-mm) was six times higher under 8 Mg ha⁻¹ of straw and 12 times higher under 16 Mg ha⁻¹ compared to unmulched treatments. Macroaggregates contained greater SOC than microaggregates in mulched soil. The SOC concentration explained the variability in aggregate properties by as much as 96%. Overall, long-term straw mulching increased SOC concentration and improved near-surface aggregate properties.