Intercropping of maize and dry beans for the Vulindlela district of KwaZulu-Natal.

Abstract

The use of a maize/bean intercropping system to improve land productivity was investigated after limited land availability had been identified (Liebenberg, 1993) as a major constraint to crop production in the Vulindlela area of the KwaZulu-Natal province of South Africa. The objective of this study was to develop an intercropping system that would: a) Give an intercrop bean yield approximately equal to that of the sole crop yield, b) Give a maize yield acceptable to the farmer (needed mainly for green maize). c) Produce a land equivalent ratio (LER) greater than one. In order to ensure high bean yields, maize dominance was reduced by lowering the normal maize population of the intercrop by 50% and by using a tramline row arrangement instead of evenly spaced rows. Two bean cultivars namely Mkuzi (carioca) and Umlazi (speckled sugar) and two maize cultivars namely Kalahari Early Pearl (KEP) (an open pollinated cultivar) and SR 52 (a hybrid) were used. Single trials were planted at four localities spread over three seasons i.e. Vulindlela and Ukulinga (1992/93), Cedara (1995/96) and Makhathini (1996). The treatments included varying bean densities, bean planting times and maize harvesting stages. These treatments were compared to maize and bean sole crop controls. High maize yields led to low bean intercrop yields. However, there was little or no difference between sole bean yield and intercrop bean yields associated with lower maize yields. Intercrop maize yields were 50% of the sole maize yields at all the sites. The mean LER's for the Vulindlela and Ukulinga trials were 1.04 and 0.96 respectively while the mean LER's for the Cedara and Makhathini trials were 1.34 and 1.31 respectively. Only the latter two trials displayed significant improvements in land productivity. Mkuzi was more affected by intercropping than Umlazi while KEP competed less with the beans than SR 52 and gave higher yields under less favourable growing conditions. Yield component studies indicated that stress during the vegetative, pod formation, and pod filling stages led to yield reduction in the dry bean crops. Light and leaf nutrient level studies suggested that the yield reduction resulted from competition for nitrogen and light. There was no competition for phosphate and potassium. The study indicates that the intercropping system did meet the desired requirements under conditions that are less than ideal for maize production, such as low soil fertility, water stress and cool temperatures.