Efficiency of soil and water conservation practices in different agro-ecological environments in the Upper Blue Nile Basin of Ethiopia

In developing countries such as Ethiopia, research to develop and promote soil and water conservation practices rarely addressed regional diversity. Using a water-balance approach in this study, we used runoff plots from three sites, each representing a different agro-ecological environment, e.g., high, mid and low in both elevation and rainfall, in the Upper Blue Nile Basin of Ethiopia to examine the runoff response and runoff conservation efficiency of a range of different soil and water conservation measures and their impacts on soil moisture. The plots at each site represented common land use types（cultivated vs. non-agricultural land use types） and slopes（gentle and steep）. Seasonal runoff from control plots in the highlands ranged 214–560 versus 253–475 mm at midlands and 119–200 mm at lowlands. The three soil and water conservation techniques applied in cultivated land increased runoff conservation efficiency by 32% to 51%, depending on the site. At the moist subtropical site in a highland region, soil and water conservation increased soil moisture enough to potentially cause waterlogging, which was absent at the lowrainfall sites. Soil bunds combined with Vetiveria zizanioides grass in cultivated land and short trenches in grassland conserved the most runoff（51% and 55%, respectively）. Runoff responses showed high spatial variation within and between land use types, causing high variation in soil and water conservation efficiency. Our results highlight the need to understand the role of the agro-ecological environment in the success of soil and water conservation measures to control runoff and hydrological dynamics. This understanding will support policy development to promote the adoption of suitable techniques that can be tested at other locations with similar soil, climatic, and topographic conditions.

Effect of Polyacrylamide integrated with other soil amendments on runoff and soil loss:Case study from northwest Ethiopia

Anionic polyacrylamide(PAM)has the potential to reduce soil erosion through soil conditioning.However,a comprehensive study about its effectiveness especially when applied combined with other amendments have rarely been conducted in the tropical highland climatic conditions,such as in Ethiopia.The study assessed the effectiveness of PAM(P=40 kg ha^(-1))alone or integrated with other soil amendments such as gypsum(G=5 t ha^(-1)),lime(L=4 t ha^(-1))and biochar(B=8 t ha^(-1))on runoff and soil loss at Aba Gerima watershed in the Upper Blue Nile basin,northwest of Ethiopia,where there is high erosion-caused soil degradation.A total of 79 daily runoff and sediment data were collected from eight runoff plots(1.3m×4m)with three replications planted with teff(Eragrostis tef)crop for two years(2018&2019)rainy seasons.Associated changes in soil physicochemical properties and crop growth parameters were investigated.Treatments reduced seasonal runoff by 12–39%and soil loss by 13–53%.The highest reduction in runoff was observed from P+B and PAM treatments while the highest reduction in soil loss was observed from that of P+L and PAM treatments.Integrating PAM with other amendments improved soil structural stability,moisture content,soil pH(P+L)and organic matter(P+B),leading to favorable environment for crop growth(biomass yield)and reduced runoff and soil erosion.Unlike PAM,biochar and lime amendments may need more time after application to be more effective.Hence continuing the field experiment and studying physico-chemical mechanisms for extended period will better elucidate their single or combined effectiveness over time.

Tillage and crop management impacts on soil loss and crop yields in northwestern Ethiopia

Lack of appropriate agronomic practices is one of the major causes for soil erosion and low yields in teff(Eragrostis tef[Zucc.])production in Ethiopia.A 3-yr study was conducted at the Aba Gerima watershed in northwestern Ethiopia,to investigate the effects of two tillage practices(reduced tillage[RT]and conventional tillage[CT]),two planting methods(row planting[RP]and broadcast planting[BP]),and two compaction options(with[+T]and without[-T]trampling)on soil loss and teff yields in a split-split plot arrangement.Sediment concentration ranged from 0.01 to 5.37 g L^(-1)(mean,0.25 g L^(-1))in our study.Accordingly,the estimated total(August-October)soil loss ranged from 0.2 to 0.5 t ha^(-1)(mean,0.3 t ha^(-1)).The sediment concentration and total soil loss were significantly influenced(P<0.05)by tillage,planting methods,and trampling only in the third monitoring year.RT reduced soil loss by 19% relative to that of CT,whereas RP resulted in a 13%reduction in soil loss over BP.The-T plots showed a 15%reduction in soil loss as compared to+T plots.Results revealed significant increase in soil total carbon and nitrogen in RT and-T.Less soil loss and greater teff grain yield were obtained in plots with improved agronomic practices(RT and RP)compared to conventional ones(CT and BP).Based on our findings we conclude that the use of RT,RP,and-T practices can effectively minimize soil loss without any crop yield penalty.

Global analysis of cover management and support practice factors that control soil erosion and conservation

Cover management and support practices largely control the magnitude and variability of soil erosion.Although soil erosion models account for their importance(particularly by C-and P-factors in the Revised Universal Soil Loss Equation),obtaining spatially explicit quantitative field data on these factors remains challenging.Hence,also our insight into the effects of soil conservation measures at larger spatial scales remains limited.We analyzed the variation in C-and P-factors caused by human activities and climatic variables by reviewing 255 published articles reporting measured or calculated C-and P-factor values.We found a wide variation in both factor values across climatic zones,land use or cover types,and support practices.The average C-factor values decreased from arid(0.26)to humid(0.15)climates,whereas the average P-factor values increased(from 0.33 to 0.47,respectively).Thus,support practices reduce soil loss more effectively in drylands and drought-prone areas.The global average C-factor varies by one order of magnitude from cropland(0.34)to forest(0.03).Among the major crops,the average C-factor was highest for maize(0.42)followed by potato(0.40),among the major orchard crops,it was highest for olive(0.31),followed by vineyards(0.26).The P-factor ranged from 0.62 for contouring in cropland plots to 0.19 for trenches in uncultivated land.The C-factor results indicate that cultivated lands requiring intensive site preparation and weeding are most vulnerable to soil loss by sheet and rill erosion.The low P-factor for trenches,reduced tillage cultivation,and terraces suggests that significantly decreased soil loss is possible by implementing more efficient management practices.These results improve our understanding of the variation in C-and P-factors and support large-scale integrated catchment management interventions by applying soil erosion models where it is difficult to empirically determine the impact of particular land use or cover types and support practices:the datasets compiled in this study can support further modeling and land management attempts in different countries and geographic regions.