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The plant nutrient status in the soils is dynamic and subject to a variety of transformations, gains and losses, depending on a number of factors including soil type, farming system and climate. Generally, soils lose plant nutrients in more ways than they gain them. The very common and obvious way is through the removal of crop harvests and residues. However, it is also known that erosion and leaching contribute immensely to the total nutrient loss from a field. In the case of nitrogen, denitrification/ volatilisation also contributes to the N loss (Stoorvogel and Smalling, 1990). For a sustainable management of nutrient systems some consideration has to be given to these losses and a balance struck between the losses and the possible gains that may occur in the field. The components of a nutrient balance with regards to nutrient losses and possible nutrient gains are shown in Figure 1. As can be seen from this figure, the main losses of nutrients from the soil are through plant uptake, leaching and soil erosion. Volatilisation only involves nitrogen and is common under anaerobic conditions making it less important when compared to the first three forms of nutrient loss. Wind erosion in Zimbabwe is minimal and confined to a few areas to justify its exclusion from the components of nutrient balance. It is however, not clear as to what percentage of total nutrient loss is lost with each of the three major components, i.e. plant uptake, soil erosion and leaching. Many investigations have shown that soil erosion results in loss of productivity, due to the modifications of the soil physical, chemical and biological composition. The degree to which these changes take place varies for the different soil types and from one agro-ecology to another (Kaihura, et al., 1998). Given the very diverse agro-climatic conditions, results from one area cannot be successfully applied to the next. However, due to limited research findings in Sub-Saharan Africa, general estimations have been made and then extended to the whole region (van Reuler and Prins, 1992). In these countries soil is an essential input to farming as agricultural production is crucial to development and the livelihoods of the

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The Significance of Soil Erosion on Soil Fertility Under Different Tillage Systems and Granitic Sandy Soils in Semi-Arid Zimbabwe: A Comparison of Nutrient Losses Due to Sheet Erosion, Leaching and Plant Uptake