Radiation interception and use in a maize and bean intercropping system

English: Food shortage is known to have been caused by overpopulation, natural disasters and poor food distribution. In areas facing food insecurity, such as Africa, peasants or smalIscale farmers have practised traditional cropping techniques since old times. One of the techniques is intercropping, and many intereropping studies have been reported since the 1960s. According to those studies, intereropping has higher productivity and also higher resource use than sole cropping, however, the contribution of crop radiation utilisation to that higher productivity is unclear. From this background, a quest as to whether intereropping was suitable to small-scale farming in a semi-arid region (Free State, South Africa) has started. The main aim of this study was to analyse and model radiation interception and employment in a maize-bean intereropping system with alternate (northsouth and east-west) row directions (Chapters 3 and 4). Also, the intererop yield advantage was assessed in terms of intensity of land use, accumulation of energy and return of cash increment (Chapter 2); and photosynthetically active radiation (PAR) above plant canopies was investigated (Chapter 5). In Chapter 2 it was shown that the maize-bean intereropping had a yield advantage, compared with the sole cropping, under the set conditions used for both maize and beans planting. In other words, maize-bean intereropping was equivalent in yield to sole maize, and gave a higher yield than sole beans. This was explained by crop radiation interception and use in Chapter 3. The intereropping was analogous to maize sole cropping in the overall efficiency of radiation interception and use, and had greater radiation interception and use than bean sole cropping. In addition, no difference in crop productivity and efficiency was found between row direction treatments. In the modelling study (Chapter 4), the intercropped maize had the same growth efficiency as the sole cropped maize, but beans had greater radiation utilisation in intereropping than in sole cropping. This resulted in an intereropping yield advantage. In Chapter 5, an empirical equation for estimating PAR from solar radiation has been introduced because PAR is not routinely measured at weather stations. The equation may be accurate enough to compute PAR from the large data sets available across southern Africa. This study has shown that planting maize in association with beans is advantageous compared with separate planting, in both crop productivity and efficiency. Normally, small-scale farmers cultivate not one crop but a staple crop and supplement crops. From this point of view, the conclusion is drawn that intereropping is suitable for use in the small-scale farming sector.