Effect of plant density and phosphate fertilizer on the growth, flower – and pod abscission, yield and yield components of pigeon peas (CAJANUS CAJAN (L.) MILLSP.)

Abstract

This thesis reports on 3 field experiments carried out in 1976 and 1976/1977 at the Field Station of the Faculty of Agriculture, University of Nairobi at Kabete. The main objective was to determine the effects of plant density and phosphate fertilizer on the growth, flower – and pod-abscission, yield and yield components of pigeon pea (Cajanus cajan (L.) Millsp.). Cultivar PPI developed at Makerere University in Uganda, as a medium maturing type and bulked at Kitale for distribution in Kenya was used. Because of lack of knowledge on the growth and development of the cultivar, observation plots were planted besides the main experiment in 1976 to provide information on growth and development. A description of the pigeon pea plant, its ecological requirements, its uses and importance in Kenya and elsewhere was given. Information available on the present topic was reviewed. Plant density nd phosphate fertilizer experiments were carried out in 1976 and 1976/77. Three levels each of plant density, 10,000, 40,000 and 81,633 plants per hectare, and phosphate fertilizer, 0, 26 and 52 kg P per hectare were used giving nine treatment combinations. The observation plots had two plant densities, 10,000 and 81,633 plants per hectare and only one phosphate fertilizer level, 26 kg P per hectare and were planted only in the 1976 experimental season. It has been found that plant density affected the growth of the cultivar. The more space available to the plants, the bigger the plants grew. The growth of the cultivar was affected by the season. The factors involved and discussed. Plant height was not affected by plant density except when soil moisture was limiting. While shoot dry weight per plant decreased with increasing density, shoot dry weight per hectare increased and did not reach its maximum at the highest density used. Plant density also affected flower-and pod-abscission, numbers of flowers, of pods and seed yield per plant. The trend of and reasons for the effects are discussed. However, plant density had no effect on the number of seeds per pod except when soil moisture was limiting, on 100 seed weight and on seed yield per hectare. The most sensitive yield component was found to be the number of pods per plant which decreased with increasing plant density. The lack of response in seed yield per hectare to plant density was attributed to the adaptability of the cultivar. Various levels of phosphate fertilizer had no effect on the growth, flower – and pod-abscission, yield and yield components. The reasons for this are discussed. The growth of the cultivar has been described at two plant densities from germination to harvest. Various growth phases of the cultivar were distinguished and discussed. The implication of various growth phases to intercropping has also been discussed. Shoot dry weight production, its distribution and relationship to seed yield at two plant densities are given. Higher plant density was found to favour vegetative growth at the expense of seed yield per pland and per hectare. Comparisons were made between leaf area indices, crop growth rates and net assimilation rates of this crop with those of others like maize, beans and Brussels sprouts. A number of areas have been identified where more research could be done before concrete conclusions on the present topic can be made.