PEDOLOGICAL ASPECTS OF LAND EVALUATION FOR IN‐FIELD RAINWATER HARVESTING IN SOUTH AFRICA

Abstract

ABSTRACTThe 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 > 150 mm, values which occur on fine‐textured soils at least 900 mm in depth. Other important characteristics are the absence of hydromorphy shallower than 700 mm, 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. Copyright © 2012 John Wiley & Sons, Ltd.