Radiation and water utilisation efficiency by mono-culture and inter-crop to suit small-scale irrigation farming

English: For small-scale irrigation farming systems to be sustainable, knowledge of the nature of these systems, their marketing constraints, labour limitations, crop, soil properties, water and climate, are just some of the aspects which need to be taken into consideration. In the light of this background a research project was started to identify the problems experienced by small-scale farmers using Participatory Rural Appraisal (PRA) approach. The PRA findings were that traditional farming practices were being neglected and that an effort needs to be made towards supplementing and encouraging small-scale irrigation farming practices. Social infrastructure, credit facilities, relevant extension and information services were not sufficient. There was lack of market incentives, market information and co-ordination in production among farmers. Lack of storage and transport facilities exacerbated this situation. Some of the agronomic problems identified with the PRA approach were later investigated through field experimentation. at the experimental site of the Agrometeorology Department (University of the Orange Free State). Production systems practised by small-scale farmers should be geared for optimum use of natural resources. Inter-crop maize/beans yielded more energy and nutrient content per hectare in most cases. The number of cobs per plant decreased with increase in plant density and a similar trend was observed in the weight of maize cobs per plant. There was no significant difference in cob number and weight per plant between inter and mono-cropping systems. Seasonal changes in the photosynthetic active radiation interception for the three inter-cropping plant densities followed the pattern of canopy development. The mean radiation use efficiency for inter-crop was 0.07 - 0.17 9 MJ-1 higher than mono-crop maize which was 1.13 - 1.42 g MJ-1. Dry matter production of inter-crop beans was lower in comparison with mono-crop beans and the reduction in inter-crop beans dry matter increased as the maize plant density increased. This was attributed to a reduction in radiation availability. Comparisons of water use at the end of the growing season indicated that mean measured cumulative water use in inter-crop maize/beans and monocrop maize were in the same order. With regard to full and supplementary irrigation, it was found that full irrigation used 100 mm more water than supplementary irrigation. A comparison of the mean water use in mono-crop maize and mono-crop beans showed statistically that mono-crop maize used more water than mono-crop beans. Comparison of water use efficiencies of inter-crop maize/beans with mono-crop maize and beans, revealed that inter-crop maize/beans produced the nutrients per hectare per millimetre (mm) of water more efficiently than mono-crop maize and mono-crop beans. Comparison of water use efficiencies for full and supplementary irrigation levels showed that supplementary irrigation was more efficient. The Putu and BEWAB models were found to be suitably accurate and user friendly for the purpose of decision support for planning small-scale irrigation farming. Putu was found to simulate both mono-crop and inter-crop maize biomass reasonably accurately. With regard to soil water content, Putu approximated the measured soil water content quite accurately in the high plant densities of intercrops and mono-crops while further work needs to be done on low and medium plant densities especially during the early growth stages of the crop. BEWAB predicted the crop water use very well with accuracy better than 80% and it was concluded that the model may be used to schedule irrigation for small-scale farmers with reasonable reliability. Putu and BEWAB can now be used for decision support .