Pedological aspects of land evaluation for in-field rainwater harvesting in South Africa. (Special Issue: Rainwater harvesting and conservation techniques for improving household food security.)

摘要

The in-field rainwater harvesting (IRWH) technique was designed for improving crop yields of subsistence farmers in semi-arid areas in South Africa. An appropriate soil survey to identify suitable land was developed by means of a field study near Thaba Nchu, South Africa. Results of the land Type Survey of South Africa (scale 1:250 000) were used to advantage. Areas suitable for IRWH on two soilscapes were delineated at a scale of 1:10 000. Although the procedure was satisfactory, to provide accuracy appropriate for small plots a scale of 1:5000 is recommended. The most important pedological characteristic of an IRWH-suitable soil is its capacity to store plant-available water, termed total extractable soil water (TESW). Satisfactory TESW values for maize and sunflower are >150mm, values which occur on fine-textured soils at least 900mm in depth. Other important characteristics are the absence of hydromorphy shallower than 700mm, and a low final infiltration rate that promotes runoff into the basins. The reliability of land evaluation for IRWH can be enhanced by using appropriate crop models together with long-term climate data to compute cumulative probability functions of yield to provide evidence regarding viability for a particular ecotope. It is concluded that the relevant technology and knowledge available in South Africa are adequate for the task ahead.