RESPONSE OF COWPEA TO RHIZOBIAL INOCULATION IN SOILS OF SOME COWPEA GROWING AREAS OF NIGER STATE

Abstract

Yield of cowpea in soils of Nigeria Savanna is often low as a result of deficiency of nutrient particularly Nitrogen. The use of rhizobia inoculants may benefit the cowpea plant through improve Biological Nitrogen Fixation. The objective of this study was to determine the response of cowpea varieties to Bradyrhizobium inoculation in soils of some cowpea growing areas of Niger State. Two greenhouse experiments were carried out at the Teaching and Research Farm of the Federal University of Technology Minna to determine (i) the size of the native rhizobial using Most Probable Number (MPN) method which was a 2 x 4 factorial experiment, and (ii) Need to Inoculate cowpea experiment laid out in a 10 x 2 x 4 x 4 fitted to a completely randomized block design. The treatment consisted of (i) proximities (close to homestead < 50 m, and far from homestead > 250 m) and (ii) cowpea varieties (Kanannado, IT93K-452-1, IT97K-499-35, and IT90K-277-2) for MPN. Treatments for need to inoculate trial consisted of (i) 10 locations (Rijau, Kontagora, Magama, Mashegu, Mariga, Bida, Paikoro, Wushishi, Chanchaga, and Bosso), (ii) 2 proximities to homestead, (iii) 4 cowpea varieties, (Proximity to homestead and cowpea varieties were the same as in the MPN experiment), and (iv) 4 nitrogen sources (N treated plants in form of urea at the rate of 100 kg N ha-1, plants inoculated with Bradyrhizobium sp. strain BR 3262 or BR 3267, and control. The result of this study shows that MPN estimate using IT90K-277-2 as the trap host (9.41 x 106 cells g-1) was significantly lower than estimates by the other varieties (1.29 - 2.23 x107 cells g-1), there was no significant difference between either of the proximities to homestead. Cowpea varieties used in this study responded to either or both inoculant strains, response to inoculation using strain BR 3262 ranged from 10.42% to 27.26% and 15.04% to 55.17% with strain BR 3267. There exists a linear relationship between symbiotic effectiveness of the native rhizobial populatons and response to inoculation. Suggesting the suitability of these inoculant strains for cultivation in the Southern Guinea savanna of Nigeria.