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Changes in land use and management strongly affect the physical and chemical properties of soils and their ecological functions. Especially, regions in East Africa have experienced dramatic land use changes in the past, but the spatial variability of soil properties and the impacts associated with those changes have been rarely documented. We investigated changes of major soil physical and chemical parameters along a gradient from hillslopes covered with forest and pasture, to the plains dominated by agriculture and savanna grassland in the upper Lambwe Valley in western Kenya. Additionally, we analyzed soil properties within a fenced area on the hillslopes in order to identify potential soil recovery effects after the exclusion of livestock grazing. We showed that topography, geological background, and soil formation processes were the primary controlling factors for variations in soil depth, the amount of rock fragments, and the textural composition of the soils. Agricultural cultivation strongly increased bulk densities and reduced hydraulic conductivity and plant available water capacity due to tillage-induced subsoil compaction. Intensive livestock grazing also increased bulk densities and negatively affected hydraulic properties although less strongly pronounced than the impacts of agricultural cultivation. Carbon and nitrogen levels were significantly lower in farmed and pasture soils compared to the forested hillslopes. For the exclusion of grazing, however, we did not observe significant differences in soil physical and chemical parameters as fencing has been maintained for few years only and natural soil recovery is a long-term process. This study provides quantitative information on the spatial distribution and variability of soil properties associated with different land use and management systems in the upper Lambwe Valley and will be of use for future research on ecosystem processes in this region. However, additional soil survey campaigns will be required to create a complete picture of the soil landscape for the entire area of the Lambwe Valley. [ABSTRACT FROM AUTHOR]

Abstract: The cultivation of row crops on mountainous farmland can generate severe soil erosion due to low ground cover, especially in the early growth stages. Organic farming, due to the absence of herbicides, can support the development of weeds and increase the ground cover compared to conventional farming. However, the benefits towards soil erosion, and the conservation potential of organic farming systems, in terms of herbicide application and weed growth, have not been investigated. Aim of this study was to identify how conventional and organic farming influence the erosion rate of soil, due to row crops cultivated on mountainous farmland in the presence or absence of agricultural chemicals. We measured multiple vegetation parameters of crops and weeds of conventional and organic farms cultivated with bean, potato, radish, and cabbage in a mountainous watershed in South Korea. We simulated the long-term soil erosion rates with the Revised Universal Soil Loss Equation (RUSLE) by using 13years of recorded rainfall data in order to account for the temporal variability of monsoonal rainfall. We determined average annual erosion rates for the study area to be between 30.6tha−1 yr−1 and 54.8tha−1 yr−1, with maximum values when radish was grown, due to the shorter growing period, higher soil disturbance at harvest, and low amounts of residue. Organic farming reduced soil loss for radish by 18% as a result of a high weed biomass density and cover at the end of the growing season. For potato, organic farming increased soil loss by 25% due to a reduced crop coverage, which is suspected to have been a consequence of crop–weed competition or increased herbivory associated with the absence of agricultural chemicals. Our results demonstrate that organic farming can potentially decrease the soil erosion risk for row crops because it supports weed development in the furrows, but it can also produce higher erosion rates when crop yields are reduced as a consequence, outweighing the protective effect of the weeds. However, the simulated erosion rates under both farming systems exceeded by far any tolerable soil loss. We conclude that organic farming alone cannot be used to effectively control erosion, and that both farming systems require additional conservation measures, such as winter cover crops and residue mulching, to sufficiently prevent soil loss for row crop cultivation. [Copyright &y& Elsevier]

Non-sustainable agricultural practices can alter the quality of soil and water. A sustainable soil management requires detailed understanding of how tillage affects soil quality, erosion, and leaching processes. Agricultural soils in the Haean catchment (South Korea) are susceptible to erosion by water during the monsoon. For years, erosion-induced losses have been compensated by spreading allochthonous sandy material on the fields. These anthropogenically modified soils are used for vegetable production, and crops are cultivated in ridges using plastic mulches. To evaluate whether the current practice of ridge cultivation is sustainable with regard to soil quality and soil and water conservation, we (i) analysed soil properties of topsoils and (ii) carried out dye tracer experiments. Our results show that the sandy topsoils have a very low soil organic matter content and a poor structure and lack soil burrowers. The artificial layering induced by spreading sandy material supported lateral downhill water flow. Ridge tillage and plastic mulching strongly increased surface runoff and soil erosion. We conclude that for this region a comprehensive management plan, which aims at long-term sustainable agriculture by protecting topsoils, increasing soil organic matter, and minimizing runoff and soil erosion, is mandatory for the future. [ABSTRACT FROM AUTHOR]