Effect of inoculation and N application on growth, yield, nodulation and N fixation ofcowpea (Vigna unguiculata)

Abstract

A series of experiments were conducted to study the effect of inoculation and N application on growth, yield, nodulation and N fixation of cowpea, involving both local and introduced varieties. In experiment 1, cowpea varieties, MI 35, Bombay and Arlington were used with (i) control (No fertilization), (ii) inoculation and (iii) fertilizer N (80 kg N h a '). In experiment 2, N fixing capacity of above three cowpea varieties was studied. In experiment 3, ten genotypes of cowpea i. e. Arlington, Bombay, MI 35, leta, CP 230, CP 889, CP 789, IT- 82 B-889, IT - 82D-789, IT - 82 E-32 were used under two N regimes, with 80 kg N ha 1 and without fertilizer (- N). All experiments were arranged in a randomized complete block design with 4 replications. Results revealed that inoculation had no effect in producing a significant yield improvement in all local cowpea varieties. In response to N fertilization, MI-35 and Arlington produced significantly higher yield (51% and 40% increase over control). Cultivar Bombay did not show a significant response to fertilizer N, but produced the highest yield compared to other cvs. without fertilizer application. Cultivar Bombay showed significantly a higher N fixing capacity than MI-35 and Arlington. Bombay and leta showed a greater nodulation capacity followed by Arlington and MI 35. Among the introduced genotypes, IT 82D 889, IT 82E 32 and IT 82D 787 showed higher nodulation potential over other genotypes at 60 days after planting (DAP). But at 75 DAP, CP 230, CP 889 and CP 789 showed superior nodulation capacity. A considerable high genotypic variability was observed among cowpea cvs. in BNF potential, total dry matter production and seed yield. Locally recommended cowpea cvs., Bombay and leta showed better nodulation capacity over introduced genotypes. N fertilizer inhibited nodulation in almost all cvs. The total dry matter production and yield responded positively to N fertilization and the effect was prominent in most of the introduced genotypes.