Assessment of Rill Erosion Development during Erosive Storms at Angereb Watershed, Lake Tana Sub-basin in Ethiopia

Application of simple and locally based erosion assessment methods that fit to the local condition is necessary to improve the performance and efficiency of soil conservation practices. In this study, rill erosion formation and development was investigated on the topo-sequence of three catchments(300-500 m slope length); and on agricultural fields(6 m and 14 m slope lengths) with different crop-tillage surfaces during erosive storms.Rill density and rill erosion rates were measured using rill cross section survey and close range digital photogrammetry. Rill formation and development was commonly observed on conditions where there is wider terrace spacing, concave slope shapes and unstable stone terraces on steep slopes. At field plot level, rill development was controlled by the distribution and abrupt change in the soil surface roughness and extent of slope length. At catchment scale, however, rill formation and development was controlled by landscape structures, and concavity and convexity of the slope. Greater rill cross sections and many small local rills were associated to the rougher soil surfaces. For instance, relative comparison of crop tillage practices have showed that faba-beantillage management was more susceptible to seasonal rill erosion followed by Teff and wheat tillage surfaces under no cover condition. Surface roughness and landscape structures played a net decreasing effect on the parallel rill network development. This implies that spatial and temporal variability of the rill prone areas was strongly associated with the nature and initial size of surface micro-topography or tillage roughness. Thus, it is necessary to account land management practices, detail micro-topographic surfaces and landscape structures for improved prediction of rill prone areas under complex topographic conditions. Application of both direct rill cross section survey and close range digital photogrammetric techniques could enhance field erosion assessment for practical soil conservation improvement.

Spatial Variability of Selected Soil Attributes under Agricultural Land Use System in a Mountainous Watershed, Ethiopia

In the Ethiopian Highlands, research projects were often measuring soil attributes of spatially structured point data but soil variability at a watershed scale is not clearly defined. This study was conducted to assess the correlation among selected soil attributes and to illustrate the spatial pattern and dependence of neighboring observations. The 53.7 km2?study watershed was divided into a 500 m by 500 m square grid using arcgis and at the center of each grid soil samples from 0 to 25 cm depth were collected within 184 locations. The descriptive statistics revealed available phosphorous (AP) had the largest coefficient of variation (CV = 104) while pH was the least variable. There was a positive link between elevation and SOC whereas bulk density (ρd) and pH indicated an inverse relationship with elevation and SOC. The value for nugget/sill of ρd, pH and elevation are less than 0.25, and depicts that it has strong spatial autocorrelation. The value for nugget/?sill of SOC, and TN found between 0.25 and 0.75, and indicate that they have moderate spatial?autocorrelation. With regard to AP, the value for nugget/sill is more than 0.75, which displays a weak?spatial autocorrelation. Semivariograms of ρd, pH and elevation were best fitted to Gaussian model whereas SOC, TN and AP were best fitted to exponential function. Generally, the study verified that soil measurements taken at the given scale through regular sampling interval were adequate to capture the spatial dependence of numerous initial soil assessments in the study watershed.

Predicting the spatial distribution of soil erodibility factor using USLE nomograph in an agricultural watershed,Ethiopia

Soil erosion in the northwestern Amhara region,Ethiopia has been a subject of anxiety,resulting in a major environmental threat to the sustainability and productive capacity of agricultural areas.This study tried to estimate soil erodibility factor(Kfactor)using Universal Soil Loss Equation(USLE)nomograph,and evaluate the spatial distribution of the predicted K-factor in a mountainous agricultural watershed.To investigate the K-factor,the 54 km2 study watershed was divided into a 500 m by 500 m square grid and approximately at the center of each grid,topsoil samples(roughly 10 to 20 cm depth)were collected over 234 locations.Sand,silt,clay and organic matter(OM)percentage were analyzed,while soil permeability and structure class codes were obtained using the United States Department of Agriculture(USDA)document.The resulting coefficient of variation(CV)of the estimated K-factor was 0.31,suggesting a moderate variability.Meanwhile,the value of nugget to sill ratio of K-factor was 0.32,which categorized as moderate spatial autocorrelation.Prediction accuracy and model fitting effect of the Gaussian semivariogram approach was best,suggesting that the Gaussian ordinary Kriging model was more appropriate for predicting Kfactor.The resulting value of the mean error(ME)was 0 and the mean squared deviation ratio(MSDR)was nearly 1,which indicates the Gaussian model was unbiased and reproduced the experimental variance sufficiently.The values of K-factor were smaller(0.0217 to 0.0188)in the northern part and gradually increased(0.0273 to 0.033 Mg h MJ^(-1)mm^(-1))towards the central and south of the study watershed.

Modeling streamflow and sediment using SWAT in Ethiopian Highlands

The coincidence of intensive rainfall events at the beginning of the rainy season and unprotected soil conditions after extreme dry spells expose the Ethiopian Highlands to severe soil erosion.Soil and water conservation measures(SWC)have been applied to counteract land degradation in the endangered areas,but SWC efficiency may vary related to the heterogeneity of the landscape.The Soil and Water Assessment Tool(SWAT)model was used to model hydrology and sediment dynamics of a 53.7 km^(2)watershed,located in the Lake Tana basin,Ethiopia.Spatially distributed stone bund impacts were applied in the model through modification of the surface runoff ratio and adjustment of a support practice factor simulating the trapped amounts of water and sediment at the SWC structure and watershed level.The resulting Nash-Sutcliffe efficiency(NSE)for daily streamflow simulation was 0.56 for the calibration and 0.48 for the validation period,suggesting satisfactory model performance.In contrast,the daily sediment simulation resulted in unsatisfactory model performance,with the NSE value of 0.07 for the calibration and–1.76 for the validation period and this could be as a result of high intensity and short duration rainfall events in the watershed.Meanwhile,insufficient sediment yield prediction may result to some extent from daily based data processing,whereas the driving runoff events and thus sediment loads occur on sub-daily time scales,probably linked with abrupt gully breaks and development.The calibrated model indicated 21.08 Mg/hm^(2)average annual sediment yield,which is far beyond potential soil regeneration rate.Despite the given limits of model calibration,SWAT may support the scaling up and out of experimentally proven SWC interventions to encourage sustainable agriculture in the Ethiopian Highlands.

SHui, an EU-Chinese cooperative project to optimize soil and water management in agricultural areas in the ⅩⅪ century

This article outlines the major scientific objectives of the SHui project that seeks to optimize soil and water use in agricultural systems in the EU and China,by considering major current scientific challenges in this area.SHui(for Soil Hydrology research platform underpinning innovation to manage water scarcity in European and Chinese cropping systems)is large cooperative project that aims to provide significant advances through transdisciplinary research at multiple scales(plot,field,catchment and region).This paper explains our research platform of long-term experiments established at plot scale,approaches taken to integrate crop and hydrological models at field scale;coupled crop models and satellite-based observations at regional scales;decision support systems for specific farming situations;and the integration of these technologies to provide policy recommendations through socio-economic analysis of the impact of soil and water saving technologies.It also outlines the training of stake-holders to develop a basic common curriculum despite the subject being distributed across different disciplines and professions.As such,this article provides a review of major challenges for improving soil and water use in EU and China as well as information about the potential to access information made available by SHui,and to allow others to engage with the project.