Highest Soil Loss Research Articles

Modelling land degradation in the Nepalese Himalaya

Land degradation is a crucial issue in mountainous areas and is manifested in a variety of processes. For its assessment, application of existing models is not straightforward. In addition, data availability might be a problem. In this paper, a procedure for land degradation assessment is described, which follows a four-step approach: (1) detection, inventory and mapping of land degradation features, (2) assessing the magnitude of soil loss, (3) study of causal factors, and (4) hazard assessment by applying decision trees. This approach is applied to a case study in the Middle Mountain region of Nepal. The study shows that individual mass movement features such as debris slides and slumps can be easily mapped by photo interpretation techniques. Application of soil loss estimation models helps get insight on the magnitude of soil losses. In the study area, soil losses are higher in rainfed crops on sloping terraces (highest soil loss is 32 tons/ha/year) and minimal under dense forest and in irrigated rice fields (less than 1 ton/ha/year). However, there is high frequency of slope failures in the form of slumps in the rice fields. Debris slides are more common on south-facing slopes under rainfed agriculture or in degraded forest. Field evidences and analysis of causal factors for land degradation helps in building decision trees, the use of which for modelling land degradation has the advantage that attributes can be ranked and tested according to their importance. In addition, decision trees are simple to construct, easy to implement and very flexible in adaptations.

Modelling land degradation in the Nepalese Himalaya

Land degradation is a crucial issue in mountainous areas and is manifested in a variety of processes. For its assessment, application of existing models is not straightforward. In addition, data availability might be a problem. In this paper, a procedure for land degradation assessment is described, which follows a four-step approach: (1) detection, inventory and mapping of land degradation features, (2) assessing the magnitude of soil loss, (3) study of causal factors, and (4) hazard assessment by applying decision trees. This approach is applied to a case study in the Middle Mountain region of Nepal. The study shows that individual mass movement features such as debris slides and slumps can be easily mapped by photo interpretation techniques. Application of soil loss estimation models helps get insight on the magnitude of soil losses. In the study area, soil losses are higher in rainfed crops on sloping terraces (highest soil loss is 32 tons/ha/year) and minimal under dense forest and in irrigated rice fields (less than 1 ton/ha/year). However, there is high frequency of slope failures in the form of slumps in the rice fields. Debris slides are more common on south-facing slopes under rainfed agriculture or in degraded forest. Field evidences and analysis of causal factors for land degradation helps in building decision trees, the use of which for modelling land degradation has the advantage that attributes can be ranked and tested according to their importance. In addition, decision trees are simple to construct, easy to implement and very flexible in adaptations.

Performance of grass and rainforest riparian buffers in the wet tropics, Far North Queensland. 2. Water quality

Riparian lands have the potential to buffer streams from hillslope sediment and nutrient transport. Most research on buffers has been conducted under laboratory or manipulated field experimental conditions. Few quantitative data exist on buffer performance under natural field conditions. This study reports measured soil loss and evaluates the effectiveness of riparian buffers on planar and convergent slopes under field hydrological conditions in Far North Queensland. The conditions are extreme for testing the effectiveness of riparian buffers as the land is steep, intensely cropped and receives high intensity rainfall. Hillslopes cropped with bananas were monitored using paired flumes. Runoff, bedload, and suspended loads were measured leaving the crop (upper sites) and leaving the riparian buffers (lower sites). Highly variable hillslope soil losses of <1 to >70 t/ha per wet season were recorded. High rates of hillslope soil loss were from areas of steep gradient with little ground cover experiencing high rainfall intensity. On planar slopes, even with high soil loss, grass buffer strips were able to trap >80% of the incoming bedload. Total N (TN), total P (TP) and suspended sediment (SS) loads were reduced between 25 and 65% by the planar slope grass buffer and within the first 15 m of the moderately convergent grass buffer. Loads leaving the moderately convergent buffer were often higher than those delivered from the crop, due to seepage after prolonged or high frequency rainfall. Under these conditions the buffer's main function is to prevent erosion rather than trap sediment and nutrients. Results from a highly convergent 5-ha hillslope, suggest that for buffers to be more effective in such topography, they should also be placed at the end of the crop rows, where contributing areas are smaller. Flow was able to concentrate within the crop and on at least one occasion was able to scour a 30-cm-wide channel through the entire width of the buffer releasing previously trapped material and making the buffer ineffective. A remnant rainforest buffer, receiving runoff from a planar slope, acted as a temporary store of sediment and nutrients that were reworked during subsequent events. This study demonstrates both a need for managed buffer strips on sloping tropical cropped land and identifies limitations on their potential effectiveness.

Land use and cover changes in the Likangala catchment of the Lake Chilwa basin, Malawi: implications for managing a tropical wetland

This study analyses land use and cover changes in the Likangala River catchment of Lake Chilwa, Malawi, an endorheic tropical African lake. It also examines how land use-related physico-chemical and hydrological parameters in two affluent rivers of the lake affect the migratory and reproductive behaviour of Barbus paludinosus and B. trimaculatus, which are migratory, ecologically and economically important fish species. Land use analysis indicated increasing deforestation and conversion of agricultural land to homestead development. High soil losses of 100t ha–1 yr–1 were estimated in the upper reaches of the catchment. High rainfall kinetic energy and poor vegetation cover were major determinants of soil loss. Sediment yield was high (374t km–2 yr–1) in the more degraded catchment of the Likangala River, compared to 315t km–2 yr–1 in the less degraded Domasi River catchment. A situation analysis for the Likangala River catchment showed that a marked reduction in soil loss occurred when a combined 20% increase of contour ridging, maize yield and tree canopy was assumed. Multiple regression analysis indicated that sediment yield, river flow rate, electrical conductivity and total suspended solids are significant predictors of the migration dynamics and reproductive status of both Barbus species. Our results suggest that the most critical soil loss factor should form an integral part of soil conservation measures in the catchment and that appropriate management actions that reduce fishing pressure on breeding Barbus females in the affluent rivers should be formulated to ensure the success of spawning migrations of breeding females into these rivers. The study further demonstrates how a combination of land use modelling, community outreach, river water quality analysis and fish population dynamics analysis can be used to identify factors useful for managing and monitoring the catchments of small tropical lakes.

Identification and Prioritisation of Critical Sub-watersheds for Soil Conservation Management using the SWAT Model

A few areas of the watershed are critical and responsible for high amount of soil and nutrient losses. Implementation of best management practices is required in those critical erosion prone areas of the watershed for controlling the soil and nutrient losses. Identification of these critical areas is essential for the effective and efficient implementation of watershed management programmes. In this study, a calibrated Soil and Water Assessment Tool (SWAT) model was verified for a small watershed (Nagwan) and used for identification and prioritisation of critical sub-watersheds to develop an effective management plan. Daily rainfall, runoff and sediment yield data of 7 years (1992–1998) were used in this study. Data related to nutrient losses for few storm events of 1997 were also used. Besides these data, the topographical map, soil map, land resources data and satellite imageries of the study watershed were used in this study. A geographical information system was used for generating the watershed and sub-watershed boundaries, drainage networks, slope, soil series and texture maps. Supervised classification method was used for land use/cover classification from satellite imageries. The weighted average values of parameters such as runoff curve number, surface slope, channel length, average slope length, channel width, channel depth, soil erodibility factor and other soil layer data were taken for each sub-watershed to verify the model. The calibrated SWAT model was verified for the monsoon season on daily basis for the year 1997 and monthly basis for the years 1992–1998 for both surface runoff and sediment yield. It was also tested for the available data on nutrient losses. Critical sub-watersheds were identified on the basis of average annual sediment yield and nutrient losses during the period of 3 years 1996–1998. The erosion rates and their classes were used as a criterion for identifying the critical sub-watersheds. Out of the 12 sub-watersheds, one sub-watershed fell under moderate soil loss group and five sub-watersheds fell under high soil loss group of soil erosion classes whereas other sub-watersheds fell under slight erosion classes. The study revealed that the SWAT model could successfully be used for identifying and prioritising critical sub-watersheds for management purposes.

Prediction of soil erosion in a Lake Victoria basin catchment using a GIS-based Universal Soil Loss model

Soil erosion patterns in watersheds are patchy, heterogeneous and therefore difficult to assess. The problem can be overcome by using predictive models. However, wide spread soil erosion model-factor parameterization and quantification is difficult due to the costs, labor and time involved. The objective of this study was to evaluate different methods of USLE input parameter derivation and to predict soil loss within a microcatchment of the Lake Victoria basin (LVB). The highest soil loss was predicted for annual cropland use (93 t ha −1year −1), followed by rangeland (52 t ha −1year −1), banana–coffee (47 t ha −1year −1), banana (32 t ha −1year −1) and forest and papyrus swamp. In the terrain units, soil loss was highest within the back slopes (48 t ha −1year −1) followed by the summits (42 t ha −1year −1) and valleys (0 t ha −1year −1). For the soil units, soil loss was highest in the Chromic Luvisols (52 t ha −1year −1) followed by Petroferric Luvisols (37 t ha −1year −1), Mollic Gleysols (5 t ha −1year −1) Dystric Planasols (0 t ha −1year −1) in large part because soil classification often correspond to various slope position.

Soil erosion under different vegetation covers in the Venezuelan Andes

This comparative study of soil erosion considered different environments in an ecological unit of the Venezuelan Andes. The soils belong to an association of typic palehumults and humic dystrudepts. Soil losses were quantified by using erosion plots in areas covered by four types of vegetation, including both natural and cultivated environments. The highest soil erosion rate evaluated corresponded to horticultural crops in rotation: reaching a value of 22 Mg ha−1 per year. For apple tree (Malus sylvestris Miller) plots, soil losses reached values of 1.96 Mg ha−1 per year. Losses from pasture (Pennisetum clandestinum Hochst. ex Chiov.) plots, without livestock grazing, were as high as 1.11 Mg ha−1 during the second year of the experiment. The highest soil losses generated from plots under natural forest were equal to 0.54 Mg ha−1 per year. Environmental factors such as total and effective rainfall, runoff, and some soil characteristics as those related to soil losses by water erosion were evaluated. The type of management applied to each site under different land use type and the absence of conservation practices explain, to a large extent, the erosive processes and mechanisms.

Erodibility and infiltration characteristics of five major soils of southwest Spain

Equations used to calculate erodibility in the Water Erosion Prediction Project soil erosion model (WEPP) are based on erodibility studies in the USA and may not function well in another region. This study was conducted to: (i) analyze erodibility and infiltration characteristics of some predominant soils of southern Spain, and (ii) test equations used to calculate interrill erodibility in the WEPP model on these soils. The five soils chosen for this study in Andalusia, southwest Spain, were: two terrace soils (referred to as ‘Red and Yellow Alfisols’), an alluvial soil (‘Fluvent’), a shallow hillside soil (‘Inceptisol’), and a cracking clay soil (‘Vertisol’). A static, solenoid operated rainfall simulator was operated at an intensity of approximately 60 mm h −1 during a 60-min dry run followed by a 30-min wet run the next day on 0.75 m 2 plots with 30% ridge slopes. Infiltration rates were high (always exceeding 50% except for the wet run of the Fluvent). The Fluvent had the lowest infiltration rate (0.00 mm min −1 at the end of the wet run) and highest soil loss (985 g m −2 h −1 in the dry run and 1557 g m −2 h −1 in the wet run). The Vertisol, Inceptisol and Red Alfisol had low soil loss (415, 605, and 527 g m −2 h −1 in the dry run and 824, 762 and 629 g m −2 h −1 in the wet run, respectively). Soil loss of the Vertisol doubled between dry and wet run and infiltration rate did not stabilize, suggesting that erodibility of Vertisols increases when they are wet. The Yellow Alfisol had lower final infiltration rate in the dry run (0.33 mm min −1) than in the wet run (0.58 mm min −1) and higher soil loss in dry run (1203 g m −2 h −1) than in wet run (961 g m −2 h −1), the reason still being unclear. Soil loss was significantly correlated to silt+very fine sand content ( r=0.96), indicating that erodibility of these soils is determined by similar properties as soils in these soil orders in the USA. However, the equation for WEPP-interrill erodibility overestimated erodibility significantly (two to four times), indicating the need to develop new erodibility equations for the Mediterranean region. Infiltration rates were generally high and soil loss rates low compared to reports from the USA, suggesting that limited runoff generation is a primary reason for low erodibility of these soils.

Temporal changes in soil aggregates and water erosion after a wildfire in a Mediterranean pine forest

The evolution of soil structure after a forest fire was studied on two zones representatives of a typical Mediterranean Pine forest. These zones were in opposite slope orientation but with similar topographical and pedological characteristics. Changes in soil macro-aggregation and water stable micro-aggregation were monitored seasonally during a year after the fire. The water erosion patterns were also studied from August 1993, immediately after the fire, to the end of 1996. The first 5 cm of soil depth were the most affected by fire temperature, showing clear differences on aggregate distribution and temporal variability between zones. In the north-facing soil, a substantial and gradual recovery on soil aggregation was observed mainly in the fraction greater than 5-mm diameter; this reached an increase of 27% in mass of aggregates. In the south slope, the evolution of aggregation was smooth and restricted to the fraction minor than 0.1 mm. These differences between zones are reflected also in their values on soil cohesiveness and compaction, being lesser in the south-oriented soils. Values of erosion parameters show that both zones have the higher soil losses during the immediate period (4 months) after the fire, being more important in the south zone. This zone produced more sediment and runoff (52.42% and 29.95%, respectively) than north-facing soils for the whole period studied.

Fator erosividade da chuva de Piraju (SP): distribuição, probabilidade de ocorrência, período de retorno e correlação com o coeficiente de chuva

Foram selecionadas 874 chuvas individuais erosivas, de uma série contínua de 23 anos de registros de dados pluviográficos. As chuvas selecionadas foram cotadas, digitalizadas e, posteriormente, analisadas. O índice de erosividade, EI30, médio anual calculado foi de 7.074 MJ mm ha-1 h-1 ano-1. Espera-se que este índice ocorra no local pelo menos uma vez a cada 2,33 anos, com uma probabilidade de 42,92%. Os valores dos índices anuais de erosividade de Piraju, esperados nos períodos de retorno de 2, 5, 10, 20, 50 e 100 anos, foram, respectivamente, de 6.696, 8.730, 10.076, 11.367, 13.039 e 14.292 MJ mm ha-1 h-1 ano-1. Foi observada uma distribuição de 78,5% do total da erosividade anual durante o semestre de outubro a março, indicando que, nesse período, era esperada a maior parte das perdas de solo por erosão. Observou-se elevada correlação entre o índice de erosividade, EI30, médio mensal e o coeficiente de chuva. Portanto, a equação de regressão determinada permite que seja estimado, com boa margem de segurança, o EI30 para outros locais que não possuam dados pluviográficos, mas que disponham de dados pluviométricos e condições climáticas semelhantes às de Piraju (SP).

Impact assessment of changes in land use/conservation practices on soil erosion in the Penedès–Anoia vineyard region (NE Spain)

Soil erosion by water is one of the most important land degradation processes in the Mediterranean basin. In comparison with other typical crops in this region, vineyards are the agricultural land use that cause the highest soil losses. The changes in land use types and management that have involved the intensification of agriculture from the 1950s have contributed to the increase of soil erosion. This paper presents an assessment of this impact in a vineyard region of fundamental concern in the NE Spain, the Penedès–Anoia, mainly dedicated to the production of high quality wines and “cavas”. The analysis is based on the comparison of the estimated soil loss rates in the period just before the mechanisation (1950s) and in the most recent past (1990s). Multitemporal data (aerial photographs and digital terrain models), the revised universal soil loss equation and GIS analysis were used for that purpose. The results show a clear negative soil loss balance, with 12.6% of the agricultural land having experienced major negative changes. This negative balance is associated with the increase of the area dedicated to vineyards, the transformation of old traditional vineyard plantations to modern trained plantations and to the removing of conservation practices to adopt plots to crop mechanisation. This leads to an unsustainable viticulture and soil degradation in medium- to long-term periods.

Conseqüências de diferentes sistemas de preparo do solo sobre a contaminação do solo, sedimentos e água por metais pesados

Este trabalho teve por objetivos determinar a influência de diferentes métodos de preparo do solo sobre as perdas por erosão de metais pesados e avaliar a contaminação dos sedimentos e da água do córrego principal da microbacia de Caetés, município de Paty do Alferes (RJ). A avaliação foi realizada durante os meses de dezembro de 1996 a março de 1997, no ciclo de cultivo do pepino (Cucumis sativus L ). Foram utilizadas parcelas do tipo Wischmeier, de tamanho de 22,0 x 4,0 m. Os tratamentos utilizados foram os seguintes: (a) aração com trator morro abaixo e queimado (MAQ); (b) aração com trator morro abaixo não queimado com restos de vegetação natural entre as linhas (MANQ); (c) aração com tração animal em nível, faixas de capim-colonião a cada 7,0 m (AA), e (d) cultivo mínimo, com preparo de covas em nível (CM). Avaliaram-se também os teores desses metais nos sedimentos de fundo e na água do córrego principal que drena a microbacia de Caetés. As perdas mais elevadas de metais pesados por erosão foram verificadas no tratamento MAQ, típico da região. Os sedimentos e a água do córrego da microbacia de Caetés mostraram incrementos nos teores totais de Cd, Ni, Pb, Zn e Mn de acordo com a posição de coleta na área. A água coletada no córrego e no açude apresentou concentrações de Cd, Mn e Pb acima dos padrões máximos estabelecidos para água potável. Os resultados obtidos neste trabalho permitem concluir que o uso intensivo de agroquímicos e as elevadas perdas de solo por erosão podem acarretar sérios riscos de contaminação da água do córrego da microbacia que é utilizada pelos animais e para irrigação.

Rainfall input generation for the European Soil Erosion Model

Abstract. A procedure to generate rainfall input for the EUROpean Soil Model is presented. To develop such a procedure, first of all the influence of rainfall event amount, rainfall event duration, and time to peak intensity of event rainfall on soil losses, calculated with EUROSEM, has been tested for several rainfall stations. Results revealed that every tested rainfall parameter had highly significant influence on computed soil loss. Therefore, distributions for each station of the dataset and for each of these rainfall parameters were calculated. To simulate rainfall event amounts, a mixed exponential distribution was applied. After transformation of rainfall event durations, their distribution could be simulated using a normal distribution. The location of the peak intensity was estimated using a kernel estimator, because no specific distribution characteristics could be identified. According to the respective distribution functions, parameter values for each of the tested rainfall event characteristic were then generated. These values were used to select rainfall events with identical parameter values out of the rainfall station-specific dataset. Computed soil losses for events selected this way were compared with soil losses calculated with available station specific rainfall event data. Comparisons for the respective means and medians generally revealed good agreement. A comparison of 75 % quartiles resulted in less good agreement, especially for test conditions with high soil losses. In general, the applied procedure was capable of simulation station-specific soil losses and of reflecting different environment conditions for the respective stations. Therefore, it seems possible to produce site specific appropriate rainfall input for EUROSEM, only with the knowledge of distributions for the investigated basic rainfall parameters. These are normally easier to obtain than long term rainfall information with high temporal resolution which would otherwise be necessary. In order to improve the procedure and make it practically useful, it will be necessary to account for seasonal changes of distributions of basic rainfall event parameters.

RESEARCH: Managing Mountainous Degraded Landscapes After Farmland Abandonment in the Central Spanish Pyrenees

/ Plant succession and pasture resources have been studied in abandoned fields of the central Spanish Pyrenees, in an environment severely affected by strong demographic pressure in the past. Several hydromorphological features (runoff and sediment yield) were also analyzed for different environments of the abandoned fields, in order to forecast the effects of their reclamation and transformation into areas for livestock use. The availability and accessibility of pastures as well as soil and water conservation is related to the process of colonization of Genista scorpius. Under a dense shrub cover both runoff and sediment yield are strongly controlled. As the shrub cover becomes open, sediment yield and runoff increase greatly. A dense herbaceous cover yields high runoff coefficients but moderate soil losses. From the results obtained, the possibility of abandoned field reclamation by means of selective clearing of scrub is discussed.KEY WORDS: Abandoned fields; Plant succession; Degraded environments; Soil erosion; Runoff; Spanish Pyrenees

Soil profile characteristics influencing runoff and soil erosion after forest fire: A case study (Valencia, Spain)

In August of 1992 a wildfire affected 9498 ha of pine forest and shrub in Sierra Calderona (Valencia, Spain). The results obtained in six stations of erosion control located in the burned are since the end of the fire are reported. Topographical, edaphological and vegetation characteristics of each station are described. Seven episodes of erosive rain with production of runoff and sediments, between August 1992 and April 1993 were studied. The data suggest that the highest soil losses were produced in the period immediately after the fire. Runoff and sediments produced in each station have been quantified. It has been observed that under similar conditions, the taxonomical and textural characteristics are determinant factors in the production of runoff and so, of soil loss.

Soil erosion due to settled upland farming in the Himalaya: a case study in Pranmati watershed

SUMMARY A common concept is that upland agriculture undertaken by local communities is a major factor causing large-scale soil erosion and other environmental problems in the Himalaya. Attempts to measure soil loss from farm fields are limited. This study was undertaken to measure the rate of soil loss from fields sown with crops during the rainy season and to examine the factors determining the erosion rates in the Pranmati watershed which is characterised by settled organic farming on terraced slopes. About 43% of the total agricultural land in the watershed was on low sloping terraces (< 2°), 32% on medium sloping terraces (2-6°) and 25% on highly sloping terraces (6-10°). Potato was the most dominant crop, occupying 50.2% of the total cropped area, followed by Amaranthus paniculatus (22.6%), Eleusine coracana (11.2%), Echinocloa frumentacea (10%) and Oryza sativa (6%). Soil loss from different crop covers was in the range of 0.300-0.658 t/ha/yr on low sloping terraces, 1–7 t/ha/yr on medium sloping terraces, and 6.037-64.39 t/ha/yr on highly sloping terraces. Comparison of different crops revealed the highest soil loss was from potato fields, a cash crop in the watershed. Potato cultivation on highly sloping terraces accounted for 72.6% of the total soil loss from agricultural fields. The area under this crop is rapidly increasing because of increasing emphasis on a monetary economy. Organic manure input in potato fields (28.5 t/ha) was much higher as compared to traditional crops (7.8-15.5 t/ha). Byproducts of potato do not have any fodder value, while the traditional crops do have useful fodder byproducts. The increase in the area under potato also implies more intensive pressure on the forests. The threat of soil erosion causing unsustainability of upland agriculture seems to be due more to the cultivation of potato than to traditional subsistence crops. Factors related to erosion and land-use policy aspects are discussed in the paper.

Run-Off and Soil Movement on Mid-Slopes in North-East Queensland [Australia] Grazed Woodlands.

Run-off, bedload and sediment concentration data were collected over a five-year period from unbounded catchments in grazed and exclosed pastures in woodlands. Cover varied from 4% during drought conditions to almost 100% in exclosed areas after above-average rainfall. High bedload soil loss, sediment concentration and run-off percentages were associated with low cover (&lt;30%). Run-off as a percentage of rainfall increased linearly with rainfall intensity; decreased linearly with cover; decreased slightly as soil moisture status declined; and reached a maximum at intermediate rainfall events. Interactions between these factors were observed. Run-off was up to 30% of rainfall in moderate rainfall events (30-40 mm) where maximum rainfall intensity over any 15 minute period (I15) exceeded 70 mm/h. When soil moisture status was high, mean run-off exceeded 30% for 40-80 mm rainfall events. For all rainfall event sizes, run-off exceeded 20% where I15 exceeded 60 mm/h. Cover had very little effect on run-off when rainfall intensity was low (I15&lt;20 mm/h), soil water deficit was low (&lt;10 mm) or when rainfall events were &gt;75 mm or &lt;10 mm. Bedload plus suspended sediment loads ranged from negligible to 1000 kg/ha/a, depending principally on cover. Soil movement from areas with &gt;40-50% cover was very low. Pastures dominated by Bothriochloa pertusa (a stoloniferous, naturalised grass) had lower run-off and lower rates of soil movement than pastures dominated by Heteropogon contortus (a native tussocky perennial grass) when compared at the same level of cover. Differences between grazed and exclosed areas could be attributed solely to differences in cover.

Evaluation of WEPP Runoff And Soil Loss Predictions Using Natural Runoff Plot Data

Model testing and evaluation are critical to the acceptance of any new prediction tool. This study was conducted to evaluate the overall performance of the Water Erosion Prediction Project (WEPP) hillslope model in predicting runoff and soil loss under cropped conditions. Natural runoff plot data, including 4,124 selected events, 556 plot years, and 34 cropping scenarios, from eight locations were selected. The average length of record for the cropping scenarios was about nine years. Several common crops and tillage systems were included. The WEPP input files for soil, slope, climate, and crop management were compiled based on measured data. The coefficient of determination (r2) between model-predicted and measured-runoff volumes for optimized Green and Ampt hydraulic conductivity (Kb) was 0.77 for selected events, 0.76 for annual values, and 0.87 for average annual values; the r2 between predicted and measured soil losses (excluding fallow and corn plots at Bethany, Mo.) was 0.36, 0.60, and 0.85, respectively. Similar predictions of runoff and soil loss were also obtained with WEPP internally estimated Kb values. Runoff and soil loss were slightly overpredicted for small storms and for years with low runoff and soil loss rates, and were underpredicted for large storms and for years with high runoff and soil loss rates. However, average runoff and soil loss rates for different cropping and management systems were adequately predicted. The accuracy and reliability of the predictions were shown to improve from an event to annual to average annual basis. Results of this study show that the WEPP model is a useful tool for predicting runoff and soil loss rates under cropped conditions.

Soil degradation by Erosion of a typic hapludalf in central Ohio and its rehabilitation

ABSTRACTSoil erosion and runoff were monitored from 1988 to 1990 on a Miamian soil (Typic Hapludalf) of 5‐6 per cent slope using field runoff plots. Four treatments were studied: (i) disk‐plough up and down the slope to 0.3 m depth (DP); (ii) disk‐plough up and down the slope followed by a protective netting (PN); (iii) uncultivated fallow without any vegetation followed by surface soil removal (R); (iv) uncultivated fallow with natural vegetation followed by ploughing (F). Mean annual runoff losses were 6, 114 and 128 mm, or 4, 20 and 18 per cent of the rainfall, and mean annual soil losses were 1.2, 85.0 and 64.0 Mg ha−1 in 1988, 1989 and 1990, respectively. Mean runoff amounts were 26, 69, 116 and 118mm and mean annual soil losses were 0.4, 23.2, 58.6 and 118 Mg ha−1 for the F, PN, DP and R treatments, respectively. In comparison with DP, PN decreased annual runoff by 40.3 per cent and annual soil loss by 79.5 per cent. The high mean soil loss for the R treatment was due to erosion following soil removal. An additional 2920 Mg ha−1 of surface soil was removed from the R treatment in May 1990. The F treatment reduced runoff by 78, 77 and 62 per cent and reduced soil loss by 99.7, 99.4 and 98.4 per cent compared with the R, DP and PN treatments, respectively. Mean losses of K, Ca, Mg and P were 1.3, 4, 1 and 01 kg ha−1, respectively for F, 3, 16, 5 and 0.3kg ha−1, respectively, for PN, 5, 31, 1 and 0.6kg ha−1, respectively, for DP, and 3, 32, 12 and 0.4 kg ha−1, respectively, for R. Soil and nutrient losses for each treatment were in the order R &gt; DP &gt; PN &gt; F. The soil organic carbon (SOC) content was significantly affected by soil erosion and management treatments, and ranged from 0.98 per cent for the R treatment to 2.3 per cent for the F treatment. Soil surface removal for the R treatment in 1990 reduced water‐stable aggregates (WSA) by 9.0 per cent, SOC by 0.6 per cent, and clay content of the uppermost 0‐50 mm depth by about 7.0 per cent. Mean total porosity (ft) ranged from 0.43 for the F to 0.52 for the DP treatment. Cumulative infiltration for 3h ranged from 13 cm for R to 34cm for PN, with corresponding infiltration rates of 4 cm h−1 and 13 cm h−1, respectively. Regardless of the treatment, there were also temporal changes in soil properties. In comparison with 1988, measurements made in 1990 showed a significant decrease in WSA of 21.3 per cent, an increase in clay content of 2.8 per cent, and a decrease in SOC of 0.39 per cent. Runoff and soil losses were significantly correlated with the mean weight diameter (MWD), SOC, bulk density (pb) and available water capacity (AWC). Plant height measured 8 weeks after planting (WAP) for the R treatment was reduced by 33.3 per cent, 33.0 per cent and 29.0 per cent compared withh DP, PN and F, respectively. Nitrogen uptake by maize plants (Zea mays L.) 10 WAP for the R treatment was lower by 15 per cent, 8 per cent, and 6 per cent compared with the DP, PN and F treatments, respectively, while P uptake was lower by 33 per cent, 32 per cent and 29 per cent, respectively, compared with the same treatments. Grain yield was 9.78 Mg ha−1 for PN, 9.76 Mg ha−1 for DP, 8.64 Mg ha−1 for F and 6.60 Mg ha−1 for R during the 1990 crop season. Grain yield was reduced by about 32.4 per cent in the R treatment compared with the PN treatment, representing a maize grain yield reduction of 158 kg ha−1 for each centimeter of soil lost.

Interrill soil erosion as affected by tillage and residue cover

No-till cropping systems are effective in reducing soil erosion. The objective of this study was to determine whether high infiltration rates and low runoff and soil loss under long-term, no-till conditions in loessial regions of the Midwest US result from both the well-structured, porous condition of the soil and the protective cover of crop residue or primarily from residue cover. Soil loss, runoff, and infiltration were measured using a rainfall simulator on interrill erosion plots with and without residue cover on a conventional and two no-till systems in central Illinois. For both conventional till and no-till conditions, removing surface residue significantly decreased infiltration rates and increased soil loss. Tilling the no-till surface while maintaining an equal surface cover as with the no-till system slightly increased interrill erosion. Removing residue on a no-till system, however, increased soil loss significantly. A no-till soil condition without adequate residue cover will seal, crust, and erode with extremely high soil losses following surface drying.