Effects of Phosphorus and Nitrogen Fertilizers on the Growth and Yield of Phaseolus Vulgaris on Degraded Soils in Uganda
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Phaseolus vulgaris L., also known as the common bean, is a major grain legume consumed worldwide for its edible seeds, pods and serves as a major protein source for the poor. However, its production is limited by low phosphorus concentrations in most soils. A bucket experiment was set up at Makerere University, Department of Environmental Management to investigate the effect of phosphorus and nitrogen fertilizers on growth and yield of the common bean on degraded soils in order to generate information needed by smallholder farmers to tackle the problem. Seven treatments (0N:0P:0K, 0N:75P:50K, 50N:0P:50K, 50N:75P:0K, 50N:25P:50K, 50N:50P:50K and 50N:75P:50K) were setup and the experiment was laid out in a Complete Randomized Block Design (CRBD) with three replicates. The buckets used had a capacity of 6kg of soil. Supplemental water was provided during days with no rainfall. An insecticide was sprayed three times to kill the bean aphids. Data collected included the average number of leaves per bean plant, the average number of pods per plant, the average number of seeds per pod per plant, the average number of root nodules per plant and the dry matter yield. General analysis of variance (ANOVA) was carried out and means were separated using standard error of difference (s.e.d) at 5 % level of significance. The results showed that T4 (50N:75P:0K) produced the highest number of leaves and bean yield, but other P levels significantly increased the growth and yield components of the common bean. It was also observed that there was no significant difference between T1 (control) and T3 (50N:0P:50K) emphasizing that for degraded soils, phosphorus deficiency seriously limits seed formation (number of pods). Based on the results obtained, the recommended application rate of phosphorus fertilizer was 75 kg/ha for degraded soils from central Uganda for better production of the common bean. In general, it is also recommended to carry out the same study in different localities with varying extents of P limitation in order generate site specific fertilizer recommendations.