Soil Bunds Research Articles

Effect of Level Soil Bund and Fayna Juu on Soil Physico-chemical Properties, and Farmers Adoption Towards the Practice at Dale Wabera District, Western Ethiopia

The objective of this study was to evaluate the effect of physical soil and water conservation (SWC) structures and slope gradients on soil properties and to identify factors affecting farmer’s adoption of the SWC practices. Cropland treated with level soil bund, fanya juu, and adjacent cropland without conservation structures were considered along the three slope gradients. A total of 27 soil samples were collected from the top 20 cm soil depth in ‘X’ design square plot with a length of 10m x 10m and replicated three times. A total of 120 households (HH) were randomly selected among which 48.3% were adopters and 51.7% were non-adopters of SWC structures. The collected soil samples were analyzed following standard laboratory procedures and a total of 10 variables were fitted in the logistic regression model. The result of the analysis revealed that sand fraction (%), SOC (%), TN (%), CEC (meq/100gm), and pH (H2O) were showed significant (P ≤ 0.05) differences between cropland treated with conservation structures and control plots; however, available P (ppm) did not show significant (P ≤ 0.05) variation. With regard to slope gradient, soil textural fractions sand (%), Silt (%) and Clay (%), and CEC (meq/100gm) were showed significant difference (P ≤ 0.05). While BD (g cm-3), SMC (%), SOC (%), TN (%), and available P (ppm) did not significantly differ along the slope. The result of the model also showed that the explanatory variables; age, education level, family size, landholding, farm experience, availability of labor shortage, and extension service were significantly affected the adoption of SWC practices by the farmers. On the other hand; sex, marital status, and livestock holding were not significantly affected farmers’ adoption of SWC practice. Therefore, scaling up of the soil bund for the area is necessary and building capacity, providing training and experience-sharing through field days for farmers is essential. Moreover, further investigation is encouraged on the integrated effect of physical and biological SWC practice and its socioeconomic aspects for a better understanding of the effect of sustainable use of the land.

Erosion Risk Potential Assessment Using GIS and RS for Soil and Water Resource Conservation Plan: The Case of Yisir Watershed, Northwestern Ethiopia

Soil erosion is more sensitive in the highlands of Ethiopia. The purpose of this study is evaluating erosion risk potential using RUSLE model with GIS and remote sensing to identify erosion potential areas for soil and water resources conservation plan and to prepare soil loss risk map. Collected data were processed and analyzed using Arc GIS10.2 version. Total average annual soil loss from the 2,120.33ha was estimated at 7161.06tons. The lower soil loss rate was 2.5t/ha/yr on plantation and natural forest, the maximum value was 100.62tons/ha/yr in steep slope cultivated land and average soil loss was 50.31 tons/ha/yr. About 6.35% of the area is under extremely very severe soil erosion rate. Level soil bund, graded soil, stone or stone faced soil bund, fanyajju, cutoff- drain in the above part of the catchment, waterway along the slope, trenches on grazing land, check dam SWC measures at Quala got, integrated physical with biological measures like tree Lucerne, Vetiver grass are the recommended SWC measures. This approach can be applied in other basin or watershed for assessment of erosion risk potential using GIS and RS, and this can be used as a preliminary watershed planning tool for decision makers in Ethiopia like Woreda Agriculture and Natural Resources management Office.

Effects of water harvesting and organic fertilizer on vineyard (Vitis vinifera L.) yield and soil moisture content under arid conditions

Water harvesting techniques increase the amount of rainfall per unit area, directing the rainwater to the crop area. The rain water is stored in the soil profile with mulch and similar applications and helps the plant to benefit during the arid periods. Water harvesting techniques can be supported with mulching and fertilizing practices in order to crop yield increase. This study was carried out on 20 years old vineyard in farmers' garden in 2015 - 2016, produced on dry conditions, with economical prescription for Kilis province. Four different doses of leonardite fertilizer were applied in combination with soil bund rainwater harvesting in the experiment. The highest soil moisture was obtained from 370 mm to 7 kg/vineyard leonardite application. The maximum plant water consumption was determined to be 389.5 mm on average from the application of 7 kg/vineyard fertilizer. The minimum plant water consumption was obtained from the control with 310.7 mm. In terms of yield, there was no difference between 5 and 7 kg/vineyard leonardite fertilizer.

Options for improving water productivity: A case study of bambara groundnut and groundnut

The study determined the best management practices for improved yield (Y) and water productivity (WPET) of groundnut and bambara groundnut under different environments. Three sites representing different agro-ecological zones of KwaZulu Natal were used (Umbumbulu, Ukulinga and Wartburg). Thirty-year historic climate data from the different sites was categorised into normal and dry seasons based on probability of exceedance. Thereafter, eight strategies included were assessed against a reference scenario that represented current practices by smallholder farmers. The eight strategies included (i) early planting, (ii) recommended planting date, (iii) late planting, (iv) mulching, (v) deficit irrigation, (vi) optimum irrigation, (vii) soil bunds, and (viii) tied ridges. The Y and WPET responses (%) to different management practices relative to the reference scenario were analysed. Frequency analyses of crop failure for every management practice were conducted. Early and late planting decreased Y and WPET of groundnut by 35% at Ukulinga. At Umbumbulu and Wartburg, late planting increased WPET by 60% during normal seasons. Early planting increased Y and WPET of bambara groundnut by 30–60% at all sites during normal seasons. Both crops responded positively to mulching, especially bambara groundnut — Y and WPET increased by up to 60% during dry seasons. Optimum irrigation increased Y by 50%, but decreased WPET by ≈ 15% for both crops. Tied ridges improved Y and WPET by up to 30% for both crops. Irrigation and soil water conservation practices mitigated crop failure during dry seasons. Groundnut was more prone to crop failure during dry periods compared to bambara groundnut.

Calibration, Validation and Performance Evaluation of Swat Model for Sediment Yield Modelling in Megech Reservoir Catchment, Ethiopia

Abstract Intensive agricultural practice in Ethiopian highlands results in increasing rates of soil erosion and reservoir sedimentation. The estimation of sediment yield and prediction of the spatial distribution of soil erosion on the upper Megech reservoir catchment enables the local governments and policymakers to maximize the design span life of the Megech reservoir through implementing appropriate soil conservation practices. For this study, the sediment yield was estimated and analyzed through hydrological modeling (SWAT). The simulated outputs of the model show that the mean annual surface runoff was 282 mm and the mean annual streamflow was 153 m3/s. Similarly, 12.33 t/ha mean annual total sediment load gets into the Megech reservoir. The model performance standard used to evaluate the model result indicates that the model was superior in performing the trend of runoff and sediment yield in both calibration and validation periods. Finally, the most erosion vulnerable sub-basins that could have a significant impact on the sediment yield of the reservoir were identified. Based on this, sub-basin 7, 25, 27, 18 and 29 were found to be the most erosion sensitive areas that could have a significant contribution to the increment of sediment yield in the Megech reservoir. Considering the land use, soil type, slope, and relief of erosion vulnerable sub-basins cut off drains, fallow land, contour ploughing, Fanya juu terraces, soil bunds combined with trenches and trees could be the possible management strategies to reduce the sediment yield in the catchment.

Soil salinity assessment and coping strategies in the coastal agricultural landscape in Djilor district, Senegal

Soil salinity remains one of the most severe environmental problems in the coastal agricultural areas in Senegal. It reduces crop yields thereby endangering smallholder farmers’ livelihood. This paper aims to investigate soil salinity pattern and relationship with some environmental factors based on 304 soil sample plots (at 0–30 cm depth) coupled with farm household survey in Djilor district, Fatick Region. Elevation, slope, groundwater depth, and normalized difference vegetation index (NDVI) values of each sample plots were extracted using the ArcGIS. Through statistical analyses, the results showed that bare land, land under fallow, rice plots and Fluvisols (soil type) registered high content of salt. Clay content, soil pH, elevation, distance to river and Fluvisols were significant factors associated with the increased salt content. Contrary to expectations, soil salinity had no relationship with groundwater depth in the study area. Ninety-six percent of the respondents were affected by salinization. Women group engaged in rice farming appeared to be more affected by soil salinity. To cope with the negative impact of soil salinity in the study area, the farmers’ strategies are the application of chemical fertilizer and manure, planting and conservation of trees, and installation of soil bunds. Smallholder farmers also expressed their need for support on adaptation and mitigation from the government or any concerned organizations involved in this environmental issue. This study provides a baseline in soil salinity assessment and helps decision makers regarding land management and salt-affected areas restoration.

Farmers’ decision to adopt watershed management practices in Gibe basin, southwest Ethiopia

Watershed management practices have been implemented to avert land degradation and to enhance people's livelihoods in the highlands of Ethiopia for several years. However, the successes of these practices have been quite limited and the main factors affecting these practices have not been examined in detail. This study intended to investigate rates and intensities of adoption of watershed management practices and to determine the main factors affecting farmers' adoption decisions in the upper Gibe basin. Data were collected from 304 household heads in six sub catchments across different topographic settings using household interview. Focus groups discussions, key informant interviews and transect walk observations were also used. Descriptive statistics and econometric models such as, multivariate and ordered probit were used to analyze the data. The results revealed that the majority of households (82.6 percent) used at least one of the six practices considered in this study. Soil bund, grass strip cultivation with soil bund and compost were the major watershed management practices adopted by farmers. Adoption rate and intensity of adoption were better for program participants and in upper and middle topographic settings. The results of the multivariate and ordered probit analysis indicated that household size, extension services, credit services, training services and perception of soil erosion had positive significant relationship with both rate and intensity of adoption of most practices. Hence, policy makers and planners need to consider labor, knowledge and awareness, and capital intensive nature of the practices for the up scaling planning and implementations of watershed intervention technologies.

Determinants for adoption of physical soil and water conservation measures by smallholder farmers in Ethiopia

Adoption rates of soil and water conservation measures remain below the expected levels in Ethiopia despite the considerable investments in reducing land degradation and improving soil fertility. This constitutes one of the key research agendas in the country. This paper underscores the need for investigating the factors hindering or facilitating the adoption of soil and water conservation measures. The study results presented in this paper are based on cross-section data collected from 408 households in eastern Ethiopia, including field observations of 790 plots selected using a multi-stage sampling procedure. A multivariate probit model was employed to analyse the determinants of adoption of three soil and water conservation measures (stone bund, soil bund, and bench terracing) at the plot level. The study findings reveal that household, socioeconomic, and institution characteristics were the key factors that influenced the adoption of soil bund, stone bund, and bench terracing conservation measures. Furthermore, there was a significant correlation among the three soil and water conservation measures, indicating that the adoption of these measures is interrelated. In particular, the results show that there was a positive correlation between stone bunds and soil bunds. However, the correlations between bench terracing and stone bunds as well as bench terracing and soil bunds were negative (implying substitutability). These results imply that the Government and other relevant organizations that are responsible for reducing land degradation in order to increase agricultural production should support the establishment and strengthening of local institutions to facilitate the adoption of soil and water conservation measures.

English

Physical soil and water conservation measures with ultimate intention of reducing sever soil erosion and its associated impact had been implemented for the last four decades in southern Ethiopia. Yet, so far the technical viability of the implemented structures weren't studied. Therefore, the objective of this study was to evaluate the technical viability of the implemented physical soil and water conservation measures and its management, maintenance and appropriateness in communal and private lands of the upper catchments of Lake Hawassa watershed. The data was collected by field observation and direct measurement of the implemented structures. Moreover, focused group discussion and key informant interview was done. Descriptive statistics was used for data analysis. The results were compared with standards.  The collected data were presented in Table and Figures. The study result showed that Level soil bund and Check dam were implemented in communal land by public participation, while Level soil bunds and Fanya- juu were found in private land. The implemented structures were appropriate for the catchment, while the layouts of most implemented structures were not as the standard. The regular maintenance and management practices were also minimal. As the result, technically deficient SWC measures were found as cause of soil erosion and witnessed that construction of SWC structure in field is not an end means by itself for effective controlling of soil erosion. To be effective the implemented SWC structures has to be appropriate for the area and technically be sound. Regular maintenance and management of the structure after implementation is also vital to achieve its very inception objective. Key words: Check dam, Level Fanya- juu, soil bund, standards. &nbsp

Effects of Soil and Water Conservation on Selected Soil Physicochemical Properties and Its Implication on Soil Productivity in Ethiopia. A Review

Soil erosion and land degradation have been a severe problem in the Ethiopian highlands due to dense population, high livestock density and intensive crop production in the area. Soil and water conservation practice is one the mechanism used to reduce soil and associated nutrient loss; thus, reduce the risk of production. Efforts were started through soil and water conservation strategy at a large scale on farmland since the mid-1970 and 1980’s. However, its effectiveness depends on specific site conditions. Therefore, reviewing the effects and implication of the soil and water conservation practices on selected soil physicochemical properties and soil productivity is essential. The study conducted in various part of the country showed that the implemented soil bund reduced annual runoff and soil loss at different rates. Soil and water conservation have improved the soil physicochemical properties on conserved cropland (BD, SMC, infiltration rate, clay content, pH, CEC, av. K, av. P, SOC and TN) than in the adjacent cropland without soil and water conservation measures. In contrast, the constructed soil and water conservation has shown no significant variations as compared to adjacent cropland in a study conducted at Dawuro zone, Southern Ethiopia. Soil and water conservation, reduce the removal of fertile topsoil and improves soil moisture, which favors crop growth as a result grain yield of the crops were increased at various rates based on agro ecology, crop type and local management practices. In general, the effect of constructed soil and water conservation had clearly showed positive impact on selected soil physicochemical properties and crop yields. Therefore, maintenance of the existing soil and water conservation structures is highly recommended to sustain its benefit, productivity and production; hence, improve the livelihood of the community. Keywords : land degradation, soil and water conservation, soil properties, soil productivity. DOI : 10.7176/JEES/9-5-02 Publication date :May 31 st 2019

English

The study was conducted in Guba-Lafto Woreda of North Wollo to find out the effect of stone faced soil bund on soil macronutrients (N, P, and K), organic carbon content, soil pH, cation exchange capacity (CEC), and soil moisture status. From two case study kebeles, two watersheds were purposively selected representing Dega (highland) and Woina dega (midland) agro ecological zones. Sixteen composite surface soil samples (0 to 20 cm depth) were collected from selected watersheds. A statistical paired samples t-test showed that, mean value of some soil parameters were significantly different at t and p-value between conserved and non-conserved farmlands. These indicated that, conservation practices reduce runoff, and helps keep nutrients on the field. The study also revealed that stone faced soil bund is essential for soil moisture retentions through reducing run-off velocity, conserving and storing water, and then increasing infiltration and percolation rates. Therefore, implementation of soil and water conservation (SWC) practices should be encouraged by different governmental and non-governmental sectors of Ethiopia, and it should be followed up by other inputs like application of organic fertilizers. Key words: Soil and water conservation, soil and water conservation measures, stone faced soil bund, soil nutrients, soil moisture.

Adaptive capacity of mountain community to climate change: case study in the Semien Mountains of Ethiopia

Climate vagary has exposed farming communities in Semien Mountains (North West Ethiopia) to repeated droughts and famines in recent years. Most of the farming communities in this area have failed to produce sufficient food and have become dependent on foreign food donations. Yet, the impact, vulnerability and adaptive capacity of the community to climate change in the above-mentioned mountain areas are not well documented. This paper examined the temporal temperature and rainfall trends, and the communities’ vulnerability to climate change as well as their adaptive capacities to the changing climate to fill the existing information gaps regarding issues called forth in the Semien Mountains and other highland environments. Data were gathered using questionnaires, interviews, focus group discussions and field observations. Information from meteorological recordings was also collected for this study. The collected data were analyzed using standardized precipitation index, livelihood vulnerability index, bi-logit model and descriptive statistics. The results confirmed highest climatic variability manifested in rainfall and temperature changes. Rainfall decreased by a total of 573.46 mm (by ≈ 16.38 mm per year on average) from 1979 to 2013. Mean annual temperature increased from 18.54 °C in 1979 to 20 °C in 2013. In this light, majority of the respondents (85%) reported facing climatic hazards. About 70% of them perceive that climate change has decreased land productivity and numerous others (74%) felt its future implications on farmlands. Recurrent crop and animal diseases were indicated by 95.21 and 93.41% of the sampled households, respectively. These climate change-induced incidents were exacerbated by lower adaptive capacities and limited institutional services. Livestock rearing, livelihood diversification, stone bund building, tree planting, organic fertilizer application, selling home articles, soil bund construction, rainwater harvesting, utilizing synthetic fertilizers and preparing hand-dug wells were important adaptive strategies used and ranked 1–10, respectively, by the studied households. Extension services, family size, farm income, access to training and livestock ownership found influential during the use of composting, terracing and tree planting to reduce the negative impact of climate change. Farmer-to-farmer extension appeared to significantly reduce composting, terrace building and tree planting at p < 0.01 level. This calls for further social and cultural related studies to explore the reasons. Climate change adaptation strategies should thus focus on enhancing households’ access to key livelihood assets such as education (training), family size, farm income, extension service, and livestock ownership opportunities.

Effects of integrated use of grass strip and soil bund on soil properties, Southern Ethiopia

Soil degradation is the major environmental and agricultural production problem in the highlands of Ethiopia. The objectives of the study were to examine farmers’ use of grass strip and soil bund to minimize soil degradation, and effects of grass strip and soil bund on basic soil properties. Structured questionnaire survey and field observations were conducted to collect data on farmers’ use of grass strips and soil bund to minimize soil erosion, improve soil fertility and crop productivity. Simultaneously, composite soil samples were collected from croplands treated with both grass strip and soil bund, and the adjacent lands treated with soil bund only. The statistical result indicates respondents sex, marital status, educational level, erosion degree, access to conservation information, contact with extension workers, and trainings were significantly (P < 0.05) and positively affect the use of grass strips while livestock and land holding sizes were significantly (P < 0.05) and negatively affect farmers use of grass strip. The interaction of land management practices (grass strip and soil bund) and slope positions was significantly (P < 0.05) affects soil clay fractions and moisture, the highest amounts was observed at lands managed with grass strip situate at lower slope position. Similarly, soil organic matter, total nitrogen, available phosphorus, and cation exchange capacity were significantly (P < 0.05) influenced by the combined effects of land management practices and slope positions, highest quantity of these properties were observed lands managed with a grass strip and soil bund in lower slope position. Hence, integrated use of soil bund with grass strip has a meaningful contribution for selected soil property improvement that enhances soil fertility and crop productivity.

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A study was conducted at Donbi watershed, Wolaita zone, southern Ethiopia to identify, describe and evaluate different introduced soil and water conservation practices and to assess farmers’ perceptions about soil erosion and conservation measures. The necessary data were generated through field measurements and structured questionnaire survey, group discussion and transect walk. The structures were evaluated by comparing the field measurement result with the recommended dimensions. The results obtained showed that level soil bund and fanya juu were the dominant structures identified in the watershed.

Effects of land use and sustainable land management practices on runoff and soil loss in the Upper Blue Nile basin, Ethiopia

Understanding the effect of land use and sustainable land management (SLM) practices on runoff and soil loss (SL) is essential for adopting suitable strategies to control soil erosion. The purpose of this study was to analyze runoff and SL from different land use types and evaluate the effectiveness of different SLM practices through monitoring runoff and sediment from 42 runoff plots (30 m × 6 m) in different agro-ecologies of the Upper Blue Nile basin of Ethiopia. Four treatments for croplands (control, soil bund, Fanya juu, and soil bund reinforced with grass) and three treatments for non-croplands (control, exclosure, and exclosure with trenches) were investigated during the rainy seasons. The results showed that runoff and SL varied greatly depending on agro-ecology, land use type, and SLM practice. Seasonal runoff ranged from 52 to 810 mm in 2015 and 37 to 898 mm in 2016, whereas SL ranged from 0.07 to 39.67 t ha−1 and 0.01 to 24.70 t ha−1. The highest rates were observed from untreated grazing land in the midland agro-ecology, largely because of heavy grazing and the occurrence of intense rain events. Runoff and SL were both significantly lower (P < 0.05) in SLM plots than in control plots. On average, seasonal runoff was reduced by 11% to 68%, and SL by 38% to 94% in SLM plots. Soil bund reinforced with grass in croplands and exclosure with trenches in non-croplands were found to be the most effective SLM practices for reducing both runoff and SL. Integrating structural and vegetative measures was therefore found to be the best way to control soil erosion and its consequences. Additional investigation is needed in consideration of ecological succession and other possible effects of these types of integrated measures, for example, the effects on soil properties, biomass, and biodiversity.

Assessment of community based watershed management practices: emphasis on technical fitness of physical structures and its effect on soil properties in Lemo district, Southern Ethiopia

BackgroundSoil erosion is one of the major causes for food insecurity, and environmental degradation in Ethiopia. To reduce erosion effects, soil and water conservation practices have been promoted at farm level and watershed scale-executed via mass-community mobilization program. In Lemo district, little information is available on suitability of soil conservation practices implemented through this program. The aim of this study was to assess technical fitness of physical soil conservation structures implemented via mass-community mobilization, its effect on soil properties, and extent of farmers participation in soil conservation practices. Field observation and physical structure component measurments were used to assess the technical fitness. Whereas, composite soil samples were collected from steep, moderate and gentle slope classes to evaluate the effects of conservation practices on soil properties. Structured questionnaire was used to assess the farmers participation in soil conservation.ResultsAs compared to nationally established specification of graded soil bund for areas similar with Lemo district, technical errors were found in bund spacing and vertical interval. The studied soil properties were not significantly (P > .05) influenced with sample distance from soil bund. But, soil moisture content, bulk density, clay, reaction, electrical conductivity, organic carbon, total nitrogen and cation exchange capacity were significantly (P < .05) affected with slope gradient. These properties become better as the slope gradient decrease. Among the study household heads, only 59.69% were participated in soil conservation activities. Land holding size, cropland slope, contacts with extension agents and training opportunity were significantly (P < .05) contributes for farmers’ participation in soil conservation activities.ConclusionsTo ensure the sustainability of watershed management practices and minimize observed technical faults on conservation structures continued technical supports, trainings, and follow-ups are required in the study area.

Integrated soil, water and agronomic management effects on crop productivity and selected soil properties in Western Ethiopia

Land degradation is a major challenge limiting crop production in Ethiopia. Integrated soil and water conservation is widely applied as a means to reverse the trend and increase productivity. This study investigated the effects of such integrated approaches at two sites, Jeldu and Diga, in Western Ethiopia. A split plot design with physical soil and water conservation in the main plots and agronomic practices in the sub plots was employed. Maize (Zea mays L.) followed by groundnut (Arachis hypogaea L.) at Diga, and wheat (Triticum aestivum) followed by faba bean (Vicia faba L.) were the test crops. Surface soils were sampled before sowing and after the crop harvest, and analyzed for selected parameters. Soil moisture content during the growing period was also monitored. The use of soil bund increased soil moisture content, and significantly (P < 0.05) increased days to flowering and maturity, kernel weight and harvest index, grain yield of the test crops, with the exception of maize. The improved agronomic practices (intercropping, fertilization and row planting) significantly (P < 0.05) increased grain yield of all the test crops. The effect of the treatments on soil parameters may require longer time to be evident. Although the increase in crop yield due to soil bund and the improved agronomic practices is eminent, economic analysis is necessary before recommending the widespread use of the improved options.

English

Establishing forest plantation on degraded rangelands play a key role in forest rehabilitation processes through afforestation or/and reforestation. In-situ rainwater harvesting has positive impact on seedling survivals at degraded rangelands. A quadrant of 10 m × 10 m of five times replication at three slope classes under area enclosure was used. Both survived seedlings and soil physical parameters were collected from three soil depth profiles (0-10, 10-20 and 20-30 cm) and then analyzed. Of the transplanted seedling to the area enclosure with pits (66.53, 46.13, and 25.66%), half-moon (66.53, 41.80, and 20.40%), and soil bund embankment (55.46, 42.60, and 28.80%) were survived at bottom, middle and upper slope classes respectively. The interaction of seedling survival in both planting methods were not significantly different at P>0.05, particularly, in half-moon and pits except soil bund embankment. Because, tree seedling rose at nursery site transplanted to the embankment of structures, that is, on the dig out soils. The conserved moisture is far from seedling roots as a result needs long roots to absorb but weak and short rooting system. Pits and half-moon showed good performance than soil embankments at bottom parts. This explains that almost all in-situ structures play a crucial role at flat land rather than middle and upper parts but highest bulk density achieved for the upper parts, which might be due to risks of soil erosion and only left with very compacted cobles. Therefore, slope gradient have implication on in-situ rainwater harvesting devices efficiencies in conserving moisture for tree seedling survival so as to establish good forest stands. Key words: Growth, in-situ rainwater harvesting, moisture stress, seedlings, survival.

Shear strength of purple soil bunds under different soil water contents and dry densities: A case study in the Three Gorges Reservoir Area, China

Purple soil bunds are embankments constructed along the contour on purple soil sloping farmlands, and play a key role in controlling soil erosion. The soil shear strength makes a significant influence to the bund stability; however, few reports have documented how purple soil shear strength responds to the soil physical properties. The main goal of the present study was to determine how indicators of soil shear strength vary with the soil water content and dry density. In this study, we collected soil samples from 3 purple soil bunds in Zhong County, in the Three Gorges Reservoir Area in China, and performed an unconsolidated undrained triaxial compression test to study the soil shear strength in terms of the cohesion (c), internal friction angle (φ), and the principal stress difference (σ1–σ3). The test results show that when the dry density was constant and the soil water content increased, the soil cohesion increased and then decreased, and the results fitted to a quadratic curve. As the soil water content increased, the internal friction angle of the soil bunds decreased and displayed a first-order exponential decay. As the soil water content increased and the confining pressure remained constant, the principal stress difference decreased rapidly. When the soil water content was constant and the dry density increased, the soil cohesion, internal friction angle, and the total principal stress difference increased, although at different rates. In general, the water content had a greater effect on the cohesion, internal friction angle, and the principal stress difference than the dry density, but there were little or no interaction between water content and dry density. Furthermore, except when the water content was 6%, the stress–strain characteristics were similar across the range of water contents. For a low water content, fixed confining pressure, and an increasing dry density, the curves gradually changed from the hardening type to the weak hardening type and then to the softening type. In most cases the curves corresponded with the hardening type as the confining pressure increased.

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.