The water budget of rainfed maize and beam intercrop

摘要

Food production in the South African Development Community (SADC) region is prominently under rainfed conditions and therefore experiences annual fluctuations due to the rainfall variability. Although the staple food of maize (Zea mays) is commonly grown in the same field as dry beans (Phaseolus vulgaris) little work has been done to characterize the soil water budget of this intercropping system. The evaportranspiration can theoretically be divided into transpiration from the leaves and evaporation from the soil surface. However, it is difficult to separate the components in field studies. In this paper the Ritchie model is used to estimate the soil surface evaporation using the fractional radiation interception which depends on the crop leaf area. The intercropping system has higher leaf area than the sole crops of both maize and beans in all seasons. Therefore, the soil surface is shaded and the canopy is more dense resulting in a lower soil surface evaporation. The water budget thus gives a higher value of transpiration for the intercrop during each of the four growing seasons. This appears to be due to the complimentary use of the water resources by the maize and bean plants in the intercropping system. This illustrates the ability of the intercrop to use the available soil water in a semi-arid environment more productively. Thus the experience of the small-holder farmers in the SADC region is based on sound physical principles of water use by the two crops.