NODULATION AND GRAIN YIELD BY COWPEA (Vigna unguiculata L. Walp.) INOCULATED WITH RHIZOBIA ISOLATES

Aiming to evaluate the nodulation and grain yield by cowpea inoculated with rhizobia isolates obtained of soil samples from Brazilian Northeast region, an experiment was carried out in Leonard jars under greenhouse conditions. The experiment was performed on a randomized block design with five replicates and five sampling times, performed at 15, 30, 45, 60 and 75 days after emergence (DAE). Nine rhizobia isolates and the recommended strain (BR 2001) were inoculated on cowpea. Besides, it were used two control treatment: mineral nitrogen (TN, applying 150 mg N plant(-1)) and an absolute control (T0). Evaluating the number of nodules per plant (NN), nodule dry mass (NDM), plant dry matter (PDM), Accumulated N (N-ac), grain dry mass (GDM) and straw dry mass of pods (DMP). Results showed that the NN, NDM, PDM and Nac content increased until 45 DAE. Although variations had been occurred after 60 DAE for these parameters, significant difference was only found for Nac content at 75 DAE. Evaluated parameters (NN, NDM, PDM and Nac) showed a high correlation with GDM. Although no statistical difference had been observed to the strain BR 2001, five of the nine Bradyrhizobia isolates provided GDM production from 1.6 to 2.4 times more than the recommended strain, indicating high potential of use of these isolates as inoculant. However, further experiments are needed, mostly under field conditions to confirm these results.