The study aimed to evaluate the contribution of biological nitrogen fixation (BNF), promoted by rhizobium strains, to development and grain yield of cowpea in Roraima. In the years 2005 and 2006 experiments were performed in cerrado and mata alterada areas, where were tested the strains INPA 03-11B, UFLA 3-84, BR3267 (recommended to the cowpea), the strains BR3299 and BR3262, two mineral nitrogen doses (50 and 80 kg ha-1 of N) and a control. The analyzed variables were: nodulation and cowpea plants dry matter production, and the grain yield in the harvest. It was observed, in the mean, that BR3262 strain provided a number and nodule dry mass significantly larger than the control, while among the recommended strains, this only occurred in a sporadic form with INPA 03-11B and BR3267. Besides, it was also observed that soil rhizobium population was determinant to plants nodulation in the experiments. Comparatively to the other strains, BR3262 together with BR3267, provided superior effectiveness in BNF to plant dry mass production. In relation to grain yield, the strain BR3267 and INPA 03-11B presented better resulted compared to UFLA 3-84, however, just the strains BR3262 provided grain yield (in the mean about 1700 kg h-1), equal to 50 kg ha-1 N dose and superior to the control in three of the four experiments performed, showing to be most suitable for cowpea inoculation in Roraima.
Vigna unguiculata; BNF; lavrado; cerrado; mata alterada; Amazon
