Response of Rice Beans (Vigna umbellata) to Different Phosphate Fertilizer Rates, Sources and Cropping Systems Established in Western Kenya

Abstract

Rice bean despite being an underutilized crop is a multipurpose legume crop with a potential of improving food security in western Kenya. Acidic soils with low phosphate and organic carbon levels limit its production. We investigated effects of four phosphate fertilizer levels and cropping systems on soils, agronomy and yield components of rice beans in Kaimosi Friends University College (KAFUCO), Rongo University and Siaya Agricultural Training Centre (ATC) farms in Vihiga, Migori, and Siaya Counties in western Kenya in the short rains of 2020 and long rains of 2021. The experiment consisted of twelve treatments replicated three times per site in a split-plot in a randomized complete block design (RCBD). The main plots comprised of three cropping systems (monocrop, conventional and MBILI (Managing Beneficial Interactions in Legume Intercrops)) while the subplots were made up of four phosphate fertilizer levels (without fertilizer (control), inorganic fertilizer (26P+22N kg ha-1), pure organic (5P+22N kg ha-1) and combined organic and inorganic fertilizers at half rates (15.5P+22N kg ha-1). Soil analysis demonstrated that the soils had low P and % organic carbon­ in all the sites. There were no significant differences in Olsen P at p = .05 in all the sites. In Kaimosi, the average number of pods produced per plant was highest in the mono cropping systems (90) for treatments with mixed organic and inorganic phosphate fertilizers. Treatments with required phosphate fertilizers had the least number of days to flowering (about 75). However, days to 75% flowering in both seasons showed no significant differences in Kaimosi University and Siaya ATC farms with significant differences exhibited in Rongo University farm between the cropping systems at p= .05. The highest average rice beans yields were recorded in Rongo university farm (1.8 ton ha-1) for the treatments with mixed organic and inorganic fertilizers in the mono cropping systems. The phosphorus agronomic efficiency was highest in treatments with pure organic matter. The partial factor productivity of phosphorus was highest in the mono cropping systems. There were significant differences in harvest indices, partial factor productivity and phosphorus agronomic efficiency in all the three sites 1.8 ton ha-1. The study therefore has recommended that phosphate fertilizers are important in the rice beans production for improved yields to be realized.