tte ultimate goals of sound soil management are to maintain the fertility and structure of the soil. Highly fertile soils produce higher crop yields while maintaining good plant cover and minimizing the erosive effects of rainfall, runoff and wind. One of the ways to achieve and maintain soil fertility is to apply organic matter which improves the cohesiveness of the soil of the soil, increases its water retention capacity and promotes a stable aggregate structure. Organic matter may be added as green manures or residue. Under no-till management, the crop residue and the roots are left as added organic matter. Green manures, which area normally leguminous crops ploughed in, have a high rate of fermentation and yield a rapid increase in soil stability (Kolenbrander 1974). However, the long-term use of the land for cropping reduces the organic carbon content. Soil erosion accounts for only part of the reduction. Biological mineralization of the carbon from the soil in situ is the most important process, particularly in semi-arid areas where bare soil summer fallows are used to conserve moisture (Rasmussen et al. 1998).
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