Phosphorus Fertilizer Rating and Rhizobia Inoculation for Improved Productivity of Cowpea in Northern Uganda

Abstract

Cowpea ( Vigna unguiculata ) is an important legume crop in the tropics and subtropical regions of the world. It is mainly grown for its leaves and grains, and to a lesser extent as a fodder crop. Cowpea is considered as the most important food grain legume in the dry savannas of tropical Africa. This study compared the yield of local ( Agondire ) and improved (SECOW 2W) cowpea varieties grown on an Oxisol. Inorganic P at levels of 0, 10, 20, and 40 kg·ha -1 was tested on each variety with or without rhizobia inoculation. The experiments were set up in a randomized complete block design and replicated thrice during the short and long rains of the 2015/2016 seasons on fifteen fields in Arua district, northern Uganda. Agondire responded significantly (P < 0.05) better than SECOW 2W when high rates of inorganic phosphorus (40 kg P ha -1 ) were applied. A significant increase of 26.4% and 28.4% in grain yield of Agondire and SECOW 2W, respectively was obtained after inoculation with rhizobia. We concluded that inoculation and P fertilizer application increased the yield of both varieties, but with inoculation, SECOW 2W performs much better at lower P fertilizer rates than Agondire . Therefore, we recommend growing of SECOW 2W under inoculation with 20 kg P ha -1 and an application of 40 kg P ha -1 for Agondire local cowpea variety in northern Uganda .