Nodulação e produção de feijão-caupi em resposta à inoculação com diferentes densidades rizobianas

Abstract

The objective of this work was to evaluate the cowpea crop response to different densities of rhizobia cells applied to the seed under field conditions. Four experiments were carried out in Brazil: two in the North Region, in an already-cultivated area and in a first-crop area; one in the Central-West Region; and one in the Southeast Region. The experimental design was a randomized complete block with four replicates. The treatments consisted of the following cell densities of the BR 3267 strain or of the BR 3262 strain: 0, 0.3, 0.6, 0.9, 1.2, 1.5, and 2.4×106 colony-forming units (CFU) per seed, plus the control treatment without inoculation and with the addition of nitrogen fertilization (70 kg ha-1 N). The evaluated variables were nodule dry weight, shoot dry weight, and dry grain yield (13% moisture). To assess nodulation, five plants were collected sequentially at 30-35 days after emergence in the second row of each plot. Nodulation responded positively to the increase in rhizobia cell density applied to the seeds. There was a linear increase in plant nodulation with the increase of inoculation density; however, not necessarily with a response in shoot biomass. The highest grain yield occurs at a density of at least 1.2×106 colony-forming units per seed.