Grain legume effects on soil nitrogen mineralization potential and wheat productivity in a Mediterranean environment

The objective of this work was to provide evidence on the effects of faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) on the dynamics of soil N availability and yield parameters of wheat (Triticum turgidum L. var. durum) in a legume–wheat rotation in comparison with the effects of the more extensively studied common vetch (Vicia sativa L.). Soil samples were taken from field plots just before wheat sowing and incubated in the laboratory to assess N mineralization potential, soil respiration and N immobilization after incorporation of legume residues. Soil after vetch cultivation showed the highest residual N and mineralization potential (120 mg N kg^?1 soil), the greatest CO₂ release and the smallest N immobilization. Smaller mineral N release (80 mg N kg^?1 soil) was shown by soil after faba bean cultivation, which, however, would be capable to support an average wheat production without fertilization. Soil after chickpea and wheat cultivation manifested no differences in residual N and mineralization or immobilization potential. Laboratory results were well correlated with grain yield and N uptake during the second season of rotation in the field. All legumes resulted in significant yield surpluses and provided N credit to the following unfertilized wheat.     

Comparing surface erosion processes in four soils from the Loess Plateau under extreme rainfall events

This research aims to improve erosion control practice in the Loess Plateau, by studying the surface erosion processes, including splash, sheet/interrill and rill erosion in four contrasting soils under high rainfall intensity (120 mm h⁻¹) with three-scale indoor artificial experiments. Four contrasting soils as sandy loam, sandy clay loam, clay loam and loamy clay were collected from different parts of the Loess Plateau. The results showed that sediment load was significantly impacted by soil properties in all three sub-processes. Splash rate (4.0–21.6 g m⁻²∙min⁻¹) was highest in sandy loam from the north part of the Loess Plateau and showed a negative power relation with the mean weight diameter of aggregates after 20 min of rainfall duration. The average sediment load by sheet/interrill erosion (6.94–42.86 g m⁻²∙min⁻¹) was highest in clay loam from middle part of the Loess Plateau, and the stable sediment load after 20 min showed a positive power relation with the silt content in soil. The average sediment load increased dramatically by rill and interrill erosion (21.03–432.16 g m⁻²∙min⁻¹), which was highest in loamy clay from south part of the Loess Plateau. The average sediment load after the occurrence of rill showed a positive power relation with clay content and a negative power relation with soil organic matter content. The impacts of slope gradient on the runoff rate and sediment load also changed with soil properties. The critical factors varied for different processes, which were the aggregate size for splash erosion, the content of silt particles and slope gradient for sheet/interrill erosion, and the content of clay particles, soil organic matter and slope gradient for rill erosion. Based on the results of the experiments, specific erosion control practices were proposed by targeting certain erosion processes in areas with different soil texture and different distribution of slope gradient. The findings from this study should support the improvement of erosion prediction and cropland management in different regions of the Loess Plateau.     

Spatial variation and interaction of runoff generation and erosion within a semi-arid, complex terrain catchment: a hierarchical approach

Purpose

Closed erosion plots have been used extensively to investigate soil loss and its spatial variation within a watershed. However, erosion rates measured on closed plots at various locations within a watershed may not reflect the “real world” conditions due to plot boundary problems. The purpose of this study was to identify runoff and sediment sources in a semi-arid, complex terrain catchment by using the data collected from open plots, nested catchments, and tunnel systems.

Materials and methods

The study catchment, in the Loess Plateau of China, was partitioned into various-level geomorphic units. Runoff and sediment discharges were measured from 55 storm events between 1963 and 1968 on open plots and nested catchments. Storm flows were also monitored in 14 rainfall events from the tunnel systems between 1989 and 1990. This study combined the data collected from the two periods to investigate runoff and sediment sources from the different geomorphic units of the catchment.

Results and discussion

On the four open plots (S1, S2, S3, and S4) of the hill slope, total runoff depths of 128.5 mm (S1), 84.3 mm (S2), 101.92 mm (S3), and 141.73 mm (S4) were recorded from all the events over the first period, which correspondingly produced total sediment yields of 3.056 kg m^?2 (S1), 9.058 kg m^?2 (S1), 42.848 kg m^?2 (S3), and 97.256 kg m^?2 (S4). The number of runoff events also varied due to a non-uniformity in runoff generation among the different geomorphic units of the catchment. Tunnel flows generally had higher mean sediment concentrations than catchment outflows. Three nested catchments located from the headwaters (C1) to the mouth of the catchment (C3) generated total runoff depths of 120.02 mm (C1), 143.92 mm (C2), and 149.43 mm (C3), and correspondingly produced sediments yields of 62.01 kg m^?2 (C1), 144.02 kg m^?2 (C2), and 123.92 kg m^?2 (C3) for the first period.

Conclusions

Significant variations in runoff and erosion existed within the catchment. The spatial variation of runoff generation on the hill slopes resulted from the variation of soil infiltration. Sediment produced from the lower hill slope zone was disproportionally higher than that from the upper hill slope zone. Nevertheless, a significant portion of the sediment eroded on the lower slope zone was caused by runoff generated from the upper slope zone. Tunnel erosion also played a significant role in sediment production.     

Effects of sheet and rill erosion on soil aggregates and organic carbon losses for a Mollisol hillslope under rainfall simulation

Purpose

Characterizations of soil aggregates and soil organic carbon (SOC) losses affected by different water erosion patterns at the hillslope scale are poorly understood. Therefore, the objective of this study was to quantify how sheet and rill erosion affect soil aggregates and soil organic carbon losses for a Mollisol hillslope in Northeast China under indoor simulated rainfall.

Materials and methods

The soil used in this study was a Mollisol (USDA Taxonomy), collected from a maize field (0–20 cm depth) in Northeast China. A soil pan with dimensions 8 m long, 1.5 m wide and 0.6 m deep was subjected to rainfall intensities of 50 and 100 mm h^?1. The experimental treatments included sheet erosion dominated (SED) and rill erosion dominated (RED) treatments. Runoff with sediment samples was collected during each experimental run, and then the samples were separated into six aggregate fractions (0–0.25, 0.25–0.5, 0.5–1, 1–2, 2–5, >?5 mm) to determine the soil aggregate and SOC losses.

Results and discussion

At rainfall intensities of 50 and 100 mm h^?1, soil losses from the RED treatment were 1.4 and 3.5 times higher than those from the SED treatment, and SOC losses were 1.7 and 3.8 times greater than those from the SED treatment, respectively. However, the SOC enrichment ratio in sediment from the SED treatment was 1.15 on average and higher than that from the RED treatment. Furthermore, the loss of <?0.25 mm aggregates occupied 41.1 to 73.1% of the total sediment aggregates for the SED treatment, whereas the loss of >?0.25 mm aggregates occupied 53.2 to 67.3% of the total sediment aggregates for the RED treatment. For the organic carbon loss among the six aggregate fractions, the loss of 0–0.25 mm aggregate organic carbon dominated for both treatments. When rainfall intensity increased from 50 to 100 mm h^?1, aggregate organic carbon loss increased from 1.04 to 5.87 times for six aggregate fractions under the SED treatment, whereas the loss increased from 3.82 to 27.84 times for six aggregate fractions under the RED treatment.

Conclusions

This study highlights the effects of sheet and rill erosion on soil and carbon losses at the hillslope scale, and further study should quantify the effects of erosion patterns on SOC loss at a larger scale to accurately estimate agricultural ecosystem carbon flux.

     

Organic manure input and straw cover improved the community structure of nitrogen cycle function microorganism driven by water erosion

Water erosion process induces differences to the nitrogen (N) functional microbial community structure, which is the driving force to key N processes at soil-water interface. However, how the soil N transformations associated with water erosion is affected by microorganisms, and how the microbial respond, are still unclear. The objective of this study is to investigate the changes of microbial diversity and community structure of the N-cycle function microorganisms as affected by water erosion under application of organic manure and straw cover. On the basis of iso-nitrogen substitution, four treatments were set up: 1) only chemical fertilizer with N 150 kg ha^?1, P₂O₅ 60 kg ha^?1 and K₂O 90 kg ha^?1 (CK); the N was substituted 20% by 2) organic manure (OM); 3) straw (SW); and 4) organic manure + straw (1:1) (OMSW). The results showed that applying organic manure and straw to sloping farmland can increase soil N contents, but reduce runoff depth, K_w, sediment yield and N loss, especially in the OMSW. Straw cover and straw + organic manure increased the diversity (Chao1) of nitrifier (AOB), and both diversity and uniformity (Shannon) of denitrifier (nirK/S) were increased in the OMSW. All erosion control measures reduced N-fixing bacteria diversity and increased their uniformity, and the combined application of organic manure and straw cover was a better erosion control measure than the single application of them. Improved soil chemistry and erodibility were the main drives for the changes of N-functional microbial community structure and the appearance of dominant bacteria with different organic materials.     

Effects of postfire seeding and fertilizing on hillslope erosion in north-central Washington,USA

After the 1998 North 25 Fire in the Wenatchee National Forest, eight study sites were established on steep, severely burned hillslopes to examine the effectiveness of postfire seeding and fertilizing treatments in increasing cover to reduce hillslope erosion, and to measure the nutrient content of the eroded sediment. At each site, four 4 by 9 m plots were located with four randomly applied treatments: seed (winter wheat, Triticum estivum) at 34 kg ha^− 1, fertilizer (75% ammonium nitrate and 25% ammonium sulfate) at 31 kg ha^− 1, seed and fertilizer, and untreated control. Sediment fences were installed at the base of each plot to measure erosion rates and sample the eroded sediments. In addition, precipitation amounts and intensities, surface cover, canopy cover, and nutrient concentrations in the eroded sediments were measured for four years after the fire. Total precipitation was below average during the four-year study period, and most erosion occurred during short duration, moderate intensity summer rainfall events. The overall first year mean erosion rate was 16 Mg ha^− 1 yr^− 1, and this decreased significantly in the second year to 0.66 Mg ha^− 1 yr^− 1. There were no significant differences in erosion rates between treatments. In the first year, the seeded winter wheat provided 4.5% canopy cover, about a fourth of the total canopy cover, on the seeded plots; however, the total canopy cover on the seeded plots did not differ from the unseeded plots. The below average precipitation in the spring after seeding may have affected the winter wheat survival rate. In the fourth year of the study, the mean canopy cover in the fertilization treatment plots was 74%, and this was greater than the 55% mean canopy cover in the unfertilized plots (p = 0.04); however, there was no accompanying reduction in erosion rate for either the seeding or fertilization treatments. Revegetation by naturally occurring species was apparently not impacted by seeding during the four years of this study. The pH of the sediment as well as the concentrations of NO₃–N, NH₄–N, and K was not affected by seeding or fertilizing. The nutrient loads in the eroded sediment were minimal, with most of the nutrient loss occurring in the first postfire year. These results confirm that seeding success is highly dependent on rainfall intensity, amounts, and timing, and that soil nutrients lost in eroded sediments are unlikely to impair the site productivity.     

Runoff- and erosion-reducing effects of vegetation on the loess hillslopes of China under concentrated flow

Evaluating the effects of revegetation on runoff and erosion reduction is essential for studying soil and water conservation on the Loess Plateau after implementation of China's Grain for Green Project. However, quantifying the influence of revegetation on the erosion caused by concentrated runoff in extreme rainstorms is still challenging. To evaluate this influence, scouring-erosion experiments were implemented in situ on the vegetated hillslope plots (GR) and bare hillslope plots (CK). The runoff-reducing effects of grass (GRR) averaged 31%, 20% and 8%, and the erosion-reducing effects of grass (GER) averaged 93%, 95% and 93% on the 5°-plots, 10°-plots and 18°-plots, respectively. The ratios of GRR to GER were 0.09–0.33, implying that the ability of vegetation to reduce erosion was greater than its ability to reduce runoff. The GRR and GER obviously decreased as the inflow rate increased, and the GRR decreased as the hillslope gradient increased, but there were no obvious differences in the GER between hillslope gradients. Vegetation could decrease the ability of the concentrated flow to carry and transport sediment and increase the energy consumption of the concentrated flow in response to hydraulic resistance. Vegetation also significantly reduced the degree of rill development. The degree of rill dissection on the GR (0.054–0.087 m² m^?2) was lower than that on the CK (0.061–0.184 m² m^?2). Our findings provide an essential reference for ecological environment and vegetation restoration on loess hillslopes.     

Slope and rainfall effects on the volume of sediment yield by gully erosion in the Souar lithologic formation (Tunisia)

The Souar lithologic formation in semi-arid Tunisia is undergoing severe gully erosion which is threatening soil and water resources. Soil conservation strategies have focused more on terracing than on gully control techniques, since the contribution of gully sediment yield in the overall soil loss from watersheds is unknown. The paper reports investigations into the sediment yield provided by head-cut as well as sidewall–floor erosion of first order gullies on gentle and steep slope catchments underlined by the Souar lithologic formation. We measured mean field sediment volumes evacuated by different headward reaches of 10 and 9 gullies located on gentle and steep slope catchments, respectively. Two equations between the length of the gully head cutting and the corresponding volume of evacuated sediment were established. The treatment with a Geographic Information System (Arc View) of air photographs of six flights from 1952 to 2000 allowed the calculation of the volume of sediment provided both by head cutting and gully sidewalls–floor erosion through the following up of gully extension in eight catchments during the five periods separating the dates of these flights. Total gully erosion was on average 1.66 m³ ha^− 1 year^− 1 for the gentle slopes and 5.603 m³ ha^− 1 year^− 1 for the steep slopes. Sidewalls–floor contribution in total erosion was on average 81.5% for the gentle slopes and 77.8% for the steep slopes. We found out that the mean annual rainfall resulting from 40 mm daily rainfall threshold explained better the variation of annual head cutting sediment yield for these five periods than any other annual rainfall resulting from lower daily rainfall thresholds. Two equations between these two variables were established both for gentle and steep slope catchments.     

Interactions between soil properties and moisture content in crust formation, runoff and interrill erosion from tilled loess soils

Soil-surface seals and crusts resulting from aggregate breakdown reduce the soil infiltration rate and may induce erosion by increasing runoff. The cultivated loess areas of northwestern Europe are particularly prone to these processes.Surface samples of ten tilled silty loamy loess soils, ranging in clay content from 120 to 350 g kg⁻¹ and in organic carbon from 10 to 20 g kg⁻¹, were packed into 0.5 m² plots with 5% slopes and subjected to simulated rainfall applied at 30 mm h⁻¹. The 120 minutes rainfall events were applied to initially field-moist soil, air-dried soil and rewetted soil to investigate the effect of soil moisture content prior to rainfall. Runoff and eroded sediments were collected at 5 minutes intervals. Aggregate stability of the soils was assessed by measuring particle-size distribution after different treatments.All soils formed seals. Runoff rates were between 70 and 90% by the end of the rainfall event for field-moist plots. There were large differences between soil runoff rates for the air-dried and rewetted plots. Interrill erosion was associated with runoff, and sediment concentration in runoff readily reached a steady-state value. Measurements of aggregate stability for various treatments were in good agreement with sealing, runoff and erosion responses to rainfall. Runoff and erosion were lower for air-dried plots than for field-moist plots, and were either intermediate or lowest for rewetted plots, depending on soil characteristics. Soils with a high clay content had the lowest erosion rate when they were rewetted, whereas the soil with a high organic-carbon content had the lowest erosion rate in air-dry conditions. The results indicate the complexity of the effect of initial moisture content, and the interactions between soil properties and climate.     

Fingerprinting Sediment Sources After an Extreme Rainstorm Event in a Small Catchment on the Loess Plateau,PR China

Soil erosion is a severe problem on China's Loess Plateau due to its fine‐grained soils and the increasing frequency of extreme rainfall events. Accordingly, this study used a 100‐year frequency rainstorm dataset to analyse sediment deposition and sources in a 27‐km² catchment with a dam field area of 0·14 km² based on the hypothesis that sediments were intercepted by the dam (before collapse) during the rainstorm event and deposited in the dam field. This study applied composite fingerprinting, which revealed the sediment source contributions and estimated sediment deposition. Sediment deposition (626·4 kg m⁻²) decreased linearly or exponentially with increasing distance from the dam. Composite fingerprints based on the optimal parameters revealed relative sediment contributions of 44·1% ± 25·5%, 37·7% ± 35·0%, 9·0% ± 11·4% and 9·2% ± 11·5% by bare ground, croplands, grassland and forests, respectively. The 5‐year cumulative sediment deposition from normal rainfall was 2·3 × 10⁴ t less than the extreme rainstorm. Bare grounds and croplands were the dominant sediment sources following both the extreme rainstorm and normal erosive rainfall events but varied at different areas of the check‐dam. Erosion patterns and start times depended on land use type, thereby affecting sediment profiles in the dam field. Furthermore, severe erosion from bare ground that were all gully slopes and gully walls occurred throughout the rainfall, whereas grasslands and forest erosion occurred earlier and croplands later. Finally, extreme rainfall promoted mass wasting on slopes, gully slopes and gully walls, which are important in determining extreme rainstorm erosion pattern variation. This study aimed to reveal erosion pattern variation under extreme rainstorm events. Copyright © 2017 John Wiley & Sons, Ltd.     

坡度与种植方式对紫色土侵蚀与养分流失的影响研究

在涪陵区水土保持监测分站内建立6个径流小区,对紫色土坡耕地水土流失进行试验监测,结果表明:各小区径流量、产沙量总体随降雨量的增大而增大.自然生态修复措施防治水土流失效果显著,3.66 m3的径流量仅有0.41 kg·m3的产沙量,可有效防治紫色土坡耕地的水土流失.采用顺坡耕作措施的小区径流量与降雨量达显著正相关,而产沙量与降雨量未显著相关.径流量和产沙量大小顺序均为25°坡耕地>20°坡耕地>10°坡耕地>15°坡耕地,在15°耕地上径流量与产沙量均为最小,但15°是否是涪陵区最适宜的耕地坡度,仍有待今后收集更多的降雨资料加以分析说明.对一次强降雨进行养分流失观测,养分流失量与径流量及产沙量大小顺序基本一致.开发建设项目弃土弃渣监测点径流量与产沙量均大大高于其他小区,说明开发建设水土保持项目中防治水土流失的重要性.     

黄土丘陵区植被类型和降雨对坡面侵蚀产沙的影响

基于定西市安家沟流域2014―2016年连续3年侵蚀性降雨产流产沙资料,研究了植被类型和降雨对坡面侵蚀产沙的影响。结果表明,侵蚀性降雨可分为3类:A雨型(短历时、中高雨强)、B雨型(中雨量、小雨强)和C雨型(大雨量、小雨强),产流产沙频次为B雨型C雨型A雨型。径流系数油松林(6.915%～9.379%)、小麦地(5.838%～9.034%)和苜蓿地(6.610%～9.671%)分别是冰草地(2.724%～5.246%)的1.7～2.5倍,是沙棘林(2.296%～3.863%)的2～3倍。A雨型的径流系数大于B雨型和C雨型,B雨型和C雨型是产流的主要降雨类型。年均土壤流失量为小麦地(1.478～3.478 t/hm~2)苜蓿地(0.558～2.079 t/hm~2)油松林(0.459～0.887 t/hm~2)冰草地(0.097～0.253 t/hm~2)沙棘林(0.012～0.038 t/hm~2)。小麦地的土壤流失量分别是油松林的3～5倍,是冰草地的14倍,在坡度10°,15°,20°年均土壤流失量分别是沙棘林的123,130,92倍。C雨型对油松林产沙量的贡献率最大,B雨型次之,A雨型最小。A雨型对沙棘林产沙量的贡献率高达79%～86%,高强度、短历时降雨是沙棘林产沙的主要雨型。A雨型对小麦地和苜蓿地产沙量贡献率随着坡度的增大而增大,在坡度20°中、高雨强是小麦地和苜蓿地产沙量增加的主要雨型。小麦地、苜蓿地、油松林、冰草地的径流深与土壤流失量之间呈极显著线性正相关关系(P0.01),土壤流失量的增速为小麦地苜蓿地油松林冰草地,随着坡度的增大产沙速度加快。研究结果可为坡面侵蚀预报模型的建立提供重要的理论依据,同时对科学指导坡面水土保持措施配置有重要的实践意义。     

东北薄层黑土区作物轮作防治坡面侵蚀的效果与C值研究

作物轮作通过影响通用土壤流失方程(USLE)中作物覆盖和管理因子C值的变化和改良土壤性质而减少坡面土壤侵蚀。基于东北薄层黑土区连续6年大豆—红小豆轮作和裸露休闲坡面小区的径流泥沙和降雨资料,分析了2011—2016年研究区侵蚀性降雨特征,探讨了作物轮作防治坡面土壤侵蚀的效果,研究了作物轮作C值的年内和年际动态变化。结果表明:研究区所有侵蚀性降雨皆发生在5—10月,其降雨量占全年降水量的32.5%～68.1%,且年内和年际分布不均。对于5°坡度的裸露小区,土壤侵蚀主要发生在6—8月,坡面径流量和土壤流失量分别为48.4mm和1 388.2t/(km~2·a);对于5°坡度的作物轮作小区,土壤侵蚀主要发生在5—7月,坡面径流量和土壤流失量分别为19.5mm和166.7t/(km~2·a)。与裸露休闲小区相比,作物轮作小区可使黑土坡面年径流量和土壤流失量减少59.7%和88.0%。大豆—红小豆轮作措施的多年平均C值为0.12,其中大豆作物的C值为0.04,变化范围0.007～0.080;红小豆作物的C值为0.38,变化范围0.28～0.46。大豆和红小豆作物的C值月变化分别为0.01～0.24和0.01～0.80,呈先减少后增加的变化趋势。大豆—红小豆轮作对东北薄层黑土区坡面土壤侵蚀防治有明显效果,研究结果可为薄层黑土区土壤侵蚀定量评价和预报模型的建立提供基础数据。     

Soil infiltration, runoff and sediment yield from a shallow soil with varied stone cover and intensity of rain

Stones on the surface of the soil enhance infiltration and protect the soil against erosion. They are often removed in modern mechanized agriculture, with unfortunate side‐effects. We evaluated experimentally the influence of surface stones on infiltration, runoff and erosion under field conditions using a portable rainfall simulator on bare natural soil in semi‐arid tropical India, because modernization and mechanization often lead to removal of these stones in this region. Four fields with varied cover of stones from 3 to 65% were exposed to three rainfall intensities (48.5, 89.2 and 136.8 mm hour^?1). Surface stones retarded surface runoff, increased final infiltration rates, and diminished sediment concentration and soil loss. The final infiltration ranged from 26 to 83% of rainfall when the rainfall intensity was 136.8 mm hour^?1. The reduction in runoff and soil erosion and increase in infiltration were more pronounced where stones rested on the soil surface than where they were buried in the surface layer. The sediment yield increased from 2 g l^?1 for 64.7% stone cover with rainfall of 48.5 mm hour^?1 to 70 g l^?1 for 3.5% stone cover with rain falling at 136.8 mm hour^?1. The soil loss rate was less than 2 t ha^?1 hour^?1 for the field with stone cover of 64.7% even when the rainfall intensity was increased to 136.8 mm hour^?1. The effects of stones on soil loss under the varied rainfall intensities were expressed mathematically. The particles in the sediment that ran off were mostly of silt size.     

Simulated rainfall evaluation of revegetation/mulch erosion control in the Lake Tahoe Basin—1: method assessment

Revegetation of road cuts and fills is intended to stabilize those drastically disturbed areas so that sediment is not transported to adjacent waterways. Sediment has resulted in water quality degradation, an extremely critical issue in the Lake Tahoe Basin. Many revegetation efforts in this semiarid, subalpine environment have resulted in low levels of plant cover, thus failing to meet project goals. Further, no adequate physical method of assessing project effectiveness has been developed, relative to runoff or sediment movement. This paper describes the use of a portable rainfall simulator (RS) to conduct a preliminary assessment of the effectiveness of a variety of erosion‐control treatments and treatment effects on hydrologic parameters and erosion. The particular goal of this paper is to determine whether the RS method can measure revegetation treatment effects on infiltration and erosion. The RS‐plot studies were used to determine slope, cover (mulch and vegetation) and surface roughness effects on infiltration, runoff and erosion rates at several roadcuts across the basin. A rainfall rate of ≈60 mm h⁻¹, approximating the 100‐yr, 15‐min design storm, was applied over replicated 0·64 m² plots in each treatment type and over bare‐soil plots for comparison. Simulated rainfall had a mean drop size of ≈2·1 mm and approximately 70% of ‘natural’ kinetic energy. Measured parameters included time to runoff, infiltration, runoff/infiltration rate, sediment discharge rate and average sediment concentration as well as analysis of total Kjeldahl nitrogen (TKN) and dissolved phosphorus (TDP) from filtered (0·45 μm) runoff samples. Runoff rates, sediment concentrations and yields were greater from volcanic soils as compared to that from granitic soils for nearly all cover conditions. For example, bare soil sediment yields from volcanic soils ranged from 2–12 as compared to 0·3–3 g m⁻² mm⁻¹ for granitic soils. Pine‐needle mulch cover treatments substantially reduced sediment yields from all plots. Plot microtopography or roughness and cross‐slope had no effect on sediment concentrations in runoff or sediment yield. RS measurements showed discernible differences in runoff, infiltration, and sediment yields between treatments. Runoff nutrient concentrations were not distinguishable from that in the rainwater used. Copyright © 2004 John Wiley & Sons, Ltd.     

Spatial variability of soil organic carbon stock in an olive orchard at catchment scale in Southern Spain

Orchards have a high potential for carbon sequestration. However, little research is available on the spatial variability at catchment scale and on the difference between the tree area and the lanes. We analyzed theik spatial variability of soil organic carbon stock, SOC_stock at 90 cm depth in an 8-ha catchment in Southern Spain with olives on a vertic soil. Results showed higher soil organic carbon concentration, SOC, in the tree area as compared to the lane up to 60 cm depth, but its impact on SOC_stock was negligible since it was compensated by the higher soil bulk density in the lane. SOC at different depths was correlated with that in the top 0–5 cm. The overall SOC_stock of the orchard was 4.14 kg m⁻², ranging between 1.8 and 6.0 kg m⁻². This SOC_stock is in the mid-lower range of values reported for olive orchards, measured at smaller scale, and similar to those other intensive field crops and agroforestry under comparable rainfall conditions. The spatial variability in SOC_stock was correlated to several geomorphological variables: elevation, cumulative upstream area, topographic wetness index, sediment transport index, and tillage erosion. Differences in SOC and SOC_stock are driven by the sediment redistribution downslope, mainly by tillage erosion, and higher soil water availability in lower areas allowing higher biomass production. These topographic indexes and the correlation between SOC in the topsoil and SOC_stock up to 90 cm should be further explored in other typology of olive orchards for facilitating the mapping of SOC_stock.     

Effect of ground‐cover type on surface runoff and subsequent soil erosion in Champagne vineyards in France

This study was conducted in Champagne vineyards in France, and the objectives were to compare the main cultivation practices in Champagne vineyards and to specify the conditions required for the optimum effect of inter‐row grass cover on runoff and erosion in experimental plots of 0.25 m² under simulated rainfall. Three types of ground cover were studied. In the bark‐and‐vine‐prunings plots, the runoff coefficient (RC) ranged from 1.3 to 4.0% and soil losses were <1 g/m²/h. In the bare soil (BS) plot, the highest RC of the study was found (80.0%) and soil losses reached 7.4 g/m²/h. In the grass cover plots, the RC and amount of eroded soil were highly variable: the RCs ranged from 0.4 to 77.0%, and soil losses were between less than 1 and 13.4 g/m²/h. Soil type, soil moisture, slope and agricultural practices did not account for the variability. In fact, the density of grass cover in the wheel tracks explained a portion of this variability. The lack of grass in the centre of the inter‐row allowed for a preferential flow and created an erosion line in the wheel tracks where the soil was compacted. This study showed that grass cover in a vineyard was not necessarily sufficient to reduce surface runoff and prevent soil erosion. To be effective, the grass cover must be dense enough in the wheel tracks of agricultural machinery to avoid RCs close to the RC achieved with BS.     

A semi-empirical model to assess uncertainty of spatial patterns of erosion

Distributed erosion models are potentially good tools for locating soil sediment sources and guiding efficient Soil and Water Conservation (SWC) planning, but the uncertainty of model predictions may be high. In this study, the distribution of erosion within a catchment was predicted with a semi-empirical erosion model that combined a semi-distributed hydrological model with the Morgan, Morgan and Finney (MMF) empirical erosion model. The model was tested in a small catchment of the West Usambara Mountains (Kwalei catchment, Tanzania). Soil detachability rates measured in splash cups (0.48–1.16 g J^− 1) were close to model simulations (0.30–0.35 g J^− 1). Net erosion rates measured in Gerlach troughs (0.01–1.05 kg m^− 2 per event) were used to calibrate the sediment transport capacity of overland flow. Uncertainties of model simulations due to parameterisation of overland flow sediment transport capacity were assessed with the Generalized Likelihood Uncertainty Estimation (GLUE) methodology. The quality of the spatial predictions was assessed by comparing the simulated erosion pattern with the field-observed erosion pattern, measuring the agreement with the weighted Kappa coefficient of the contingency table. Behavioural parameter sets (weighted Kappa > 0.50) were those with short reinfiltration length (< 1.5 m) and ratio of overland flow power α to local topography power γ close to 0.5. In the dynamic Hortonian hydrologic regime and the dissected terrain of Kwalei catchment, topography controlled the distribution of erosion more than overland flow. Simulated erosion rates varied from − 4 to + 2 kg m^− 2 per season. The model simulated correctly around 75% of erosion pattern. The uncertainty of model predictions due to sediment transport capacity was high; around 10% of the fields were attributed to either slight or severe erosion. The difficult characterisation of catchment-scale effective sediment transport capacity parameters poses a major limit to distributed erosion modelling predicting capabilities.     

Contribution of sewage sludge to erosion control in the rehabilitation of limestone quarries

The aim of this study was to evaluate the effects of high doses of municipal sludge on soil aggregation and to assess its value for soil erosion reduction, both under natural and in simulated rainfall conditions. Doses of 200 and 400 Mg ha⁻¹ sewage sludge (dry weight) were applied to the soil of experimental plots situated on a 28 degree slope. Two sludge application procedures were tested: pre-mixing into the soil before disposal on the slope, and direct application on the soil surface. Sheet erosion was measured by collecting the sediment carried down to a Gerlach trough situated at the base of the plots. Simulated rainfall, with an intensity of 64 mm h⁻¹, was applied to evaluate soil erodibility. When the soil had no vegetation, the erosion measured on plots treated with sludge represented less than 10 per cent of the erosion from the control plot. Even when the vegetation was well developed, the erosion was also lower in the plots where sludge had been applied. In simulated rainfall, the soil loss was inversely proportional to the sludge dose, and when sludge was applied directly on the soil surface the erosion rates and particle mobilization caused by raindrop impact were minimal. Sludge amendments increase infiltration rates and improve soil structure, increasing the mean weight diameter of aggregates and their water resistance.     

Influence of crop residue management, cropping system and N fertilizer on soil N and C dynamics and sustainable wheat (Triticum aestivum L.) production

Management of N is the key for sustainable and profitable wheat production in a low N soil. We report results of irrigated crop rotation experiment, conducted in the North West Frontier Province (NWFP), Pakistan, during 1999–2002 to evaluate effects of residue retention, fertilizer N application and mung bean (Vigna radiata) on crop and N yields of wheat and soil organic fertility in a mung bean–wheat sequence. Treatments were (a) crop residue retained (+residue) or (b) removed (−residue), (c) 120 kg N ha⁻¹ applied to wheat, (d) 160 kg N ha⁻¹ to maize or (e) no nitrogen applied. The cropping system was rotation of wheat with maize or wheat with mung bean. The experiment was laid out in a spit plot design. Postharvest incorporation of crop residues significantly (p < 0.05) increased the grain and straw yields of wheat during both years. On average, crop residues incorporation increased the wheat grain yield by 1.31 times and straw yield by 1.39 times. The wheat crop also responded strongly to the previous legume (mung bean) in terms of enhanced grain yield by 2.09 times and straw yield by 2.16 times over the previous cereal (maize) treatment. Application of fertilizer N to previous maize exerted strong carry over effect on grain (1.32 times) and straw yield (1.38 times) of the following wheat. Application of N fertilizer to current wheat produced on average 1.59 times more grain and 1.77 times more straw yield over the 0 N kg ha⁻¹ treatment. The N uptake in wheat grain and straw was increased 1.31 and 1.64 times by residues treatment, 2.08 and 2.49 times by mung bean and 1.71 and 1.86 times by fertilizer N applied to wheat, respectively. The soil mineral N was increased 1.23 times by residues, 1.34 times by mung bean and 2.49 times by the application of fertilizer N to wheat. Similarly, the soil organic C was increased 1.04-fold by residues, 1.08 times by mung bean and 1.00 times by the application of fertilizer N. We concluded that retention of residues, application of fertilizer N and involvement of legumes in crop rotation greatly improves the N economy of the cropping system and enhances crop productivity in low N soils.