Strategic nutrient management of field pea in southwestern Uganda

The highlands of southwestern Uganda account for the bulk of field pea ( Pisum sativum L.) produced and consumed in the country. The crop fetches a stable price, which is as high as that of beef, but it has remained outside the mainstream of the research process. Low soil fertility, unfortunately, is poised to eliminate the crop. Nitrogen, phosphorus and potassium have variously been reported as deficient on the bench terraces where crop production is primarily done. Strategic nutrient management requires that the most limiting nutrient is known in order to provide a foundation for designing effective and sustainable soil fertility management interventions. A study was conducted on upper and lower parts of the bench terraces on the highlands in south-western Uganda to identify the most required macro-nutrient(s) in field pea production. Treatments included: 0 and 25 kg N ha-1, 0 and 60 kg P ha-1, and 0 and 60 kg K ha-1, all applied factorially in a randomized complete block design. Parameters assessed included nodulation, nodule effectiveness for BNF and dry weight, shoot dry weight, and grain yield. Nutrient applications that resulted in the highest crop responses were considered as most required, and hence, most limiting to plant growth and yield. Phosphorus based nutrient combinations gave the highest increments in total and effective nodule numbers, as well as dry weight, irrespective of terrace position. On the other hand, N based combinations led to the highest shoot dry matter at flowering (39 % higher over the control). The superiority of N was carried over up to final harvesting, with stover and grain yields edging out the other treatment regimes on either terrace positions. Phosphorus was most limiting nutrient, though the effect manifested in terms of the intensity of BNF indicators, followed by nitrogen, that manifested at later stages of crop growth influencing stover and grain yield.