| dc.description.abstract | A micro meteorological study was carried out at the National Dryland Farming Research station at Machakos, Kenya, to assess the potential of alley cropping Katumani Composite B maize with cassia siamea as a low-external input technology for farmers in a tropical semi-arid environment. The experimental layout was a completely randomised design with three treatments which were replicated four times. Three rows of maize were planted in each alley formed by four Cassia siamea hedgerows. The Cassia siamea was pruned to a height of 50cm two weeks before planting of the maize and the biomass incorporated uniformly into the top-soil of the cropped alleys as a source of manure. The control plots had no Cassia siamea hedges nor did they receive any prunings. To assess the influence of Cassia siamea on the yield of maize, the following parameters were measured: global radiation, soil moisture, .soil temperature, root distribution, transpiration and photosynthetic rates of the maize, plant height and maize grain yield. The calibration results of the tube solarimeters showed that their output was influenced by energy balance and geometrical factors. The geometric errors became less with EjW mounting of the tubes compared to NjS mounting. The NjS mounting was also confirmed to introduce errors that lead to wrong radiation extinction values under tropical crop canopies. These results indicate that under tropical conditions, N/S mounting of the solarimeter tubes should be avoided. The zenith angle response of the sensors is one of the most original results of this study which had not been reported in the literature. The study also found out that the assessment of the near infrared radiation (NIR) , and hence the photosynthetically active radiation (PAR), is not reliable due to the deterioration of the gelatin filters under tropical weather conditions. These changes in the filters had also not been reported in the literature. For certain purposes, the study demonstrated that near-surface soil temperatures can be used to approximate shading effects in intercropping studies. The calibration results of the gypsum blocks confirmed the existence of significantly larger sensitivity differences between similar units obtained from different manufacturers, than had been reported in the literature. The resistance units were found to suffer in the drying cycle from significant time lag of suction behind that of the soil. They also exhibited appreciable variability among themselves. However, in the important soil drying stages, their relative trends were often correct and therefore useful. Thus , despite these operational problems, the units can still be used to give relative trends of the wetting and drying of the soil, but for absolute data, they must have individual calibrations before and after a measuring period. The results of shade quantification revealed that the maize rows closest to the hedges experienced some shading during the experimental seasons but the photosynthetic effects of this shading were insignificant relative to the effects of the other factors investigated. Regarding soil moisture, the results showed that soil water extraction was higher in the agroforestry (AF) treatment than in the control. On average, the middle maize rows experienced higher soil moisture depletion than the maize rows adjacent to the hedgerows. The results from the study revealed that shading by the Cassia siamea hedges significantly depressed soil temperatures in the Western and Eastern parts of the alley relative to the centre of the alley and the controls. The depression of soil temperature was greater in the Eastern than in the Western parts of the alley. The results of the study of the feeder roots of maize and Cassia siamea showed considerable overlap of the two root systems at critical stages, particularly in the middle of the alleys and in the control plots. Midday transpiration and photosynthetic rates of the maize showed that only under low soil moisture availability were there statistically significant between-treatment differences. There were no statistically significant within-treatment differences. The observed within-treatment differences in the grain yield of maize were not statistically significant except in the shot rains of 1988. A bivriate linear regression analysis revealed that above about 150mm of total seasonal rainfall, the grain yield per row in the AF treatment was higher than in the control but below this rainfall, the converse was true. These between-treatment maize yield differences were statistically significant except in the long rains of 1987. The grain yield patterns across the alleys followed the observed soil temperature patterns. The highest competition for water and nutrients existed in the middle of the alley, where the overlap between the two root systems was greatest. This also partly led to the observed yield profiles across the alleys. The observed variations in grain yield among the control plots were likely due to the greater Cassia siamea root excursion into the plots bordered on two sides by Cassia siamea hedges, compared to those plots which had hedges on one side only. From the results of this study, it is concluded that the higher maize yield in the AF treatment is in most seasons not enough to compensate for the land "lost" to the hedgerows due to competition for water and nutrients under the relatively low mulch inputs. The results suggest that alley cropping in semi-arid areas needs to have a strong protective component of crops and/or soils to be of interest to the farmers. For the time being therefore, the farmers in the region should not be advised to adopt this system, since Cassia siamea does not contribute sufficiently to soil fertility to justify land and labour costs. Another conclusion from this work is that many aspects of alley cropping under competitive semi-arid conditions have not yet been researched on. Many areas of research are therefore recommended to examine alternative approaches. Finally, it should be said that this study has made important contributions regarding the use of various research equipment under tropical conditions and towards the understanding of the limits of alley cropping as an alternative cropping system for resource poor farmers under semi-arid conditions. | |
