AN ANALYSIS OF SOIL LOSS MEASUREMENTS ON SMALL AGRICULTURAL PLOTS AND THE IMPLICATIONS FOR SOIL CONSERVATION IN KONDOA DISTRICT, TANZANIA.

摘要

This study investigates the relations between agriculture and the physical environment with soil loss. The field observations are undertaken on twenty farms within Kondoa District in Central Tanzania. Field work was conducted during the major growing season in 1984-1985. Primary focus is on phenomena related to rainsplash and unconcentrated runoff. The primary goals of the research are to determine the magnitude of soil loss in the area as a whole; to identify the dominant geomorphic processes that determine the variability of soil loss throughout the district; to establish which areas are undergoing land degradation, from an agricultural perspective; to identify conservation practices that will be effective in reducing soil loss; and finally to evaluate the effectiveness of existing land use practices in controlling soil loss.; Soil loss data were gathered weekly by installing sediment traps on twenty plots representing the major agricultural settings in the area. Factors affecting soil erosion, as identified by the Universal Soil Loss Equation, form the conceptual basis of the study. Rainfall amounts were collected between December 1984 and May 1985. Sites of uniform slope were used to minimize the variability of soil losses due to complex slope relations. Percentage land cover was approximated at monthly intervals to determine the role of groundcover on erosion. The volume and direction of splash material displacement was determined using splashboards. Material for analysis was collected weekly from each location.; Results indicate that total rainfall is the most significant variable affecting the displacement of material by splash, soil loss per unit area and net downslope soil movement. Thus soil erosion is a major problem for long-term agricultural production.; To reduce current erosion trends, it is imperative that existing land use practices conform with the fragility of the physical environment. Conservation practices must be directed to the few rain events that cause significant erosion. In this case crops must be planted early for them to establish an adequate groundcover during the rainy season. Also mixed cropping must be popularized and should include fast maturing crops that establish an early groundcover. In some cases multiplanting is desirable to create an extensive root network and a canopy cover that offsets rain-splash and surface runoff. (Abstract shortened with permission of author.)