干旱区生态环境知识资源中心

Agricultural systems in South Africa have been developed under primarily arid and semi-arid climatic conditions where droughts are common. Adoption of agricultural practices by farmers maximizes precipitation utilization, ensure production, economic and social sustainability. Precipitation use efficiency (PUE, kg produce ha(-1) mm (-1) rainfall plus the change in soil water content of the root zone) proved to be a valuable parameter for comparing the level of precipitation utilization of different production or management practices for dryland crop production or rangeland utilization. Increasing the length of the fallow period before planting increased the amount of pre-plant stored water in the soil thereby reducing the risk of drought damage to crops that resulted also in better yields. Deep drainage occurred only on sandy soils during wet seasons and values as high as 20% of the annual precipitation were measured during years of above average precipitation. In the experiments reported soil cultivation generally increased runoff. The retention of large amounts(>6 t ha(-1)) crop residue on the soil surface is required to decrease runoff from cultivated fields. Between 50 and 75% of the annual precipitation is lost through evaporation from the soil surface thus resulting in relatively low PUE-values. (C) 2001 Elsevier Science B.V. All rights reserved.