Foliar application of molybdenum in common bean. III. Effect on nodulation

Abstract

Two field experiments were conducted, one in Viçosa, Brazil (high fertility soil), and the other in Coimbra, Brazil (low fertility soil) to verify the effect molybdenum (Mo), nitrogen (N), or Rhizobium on growth of common bean (Phaseolus vulgaris). Plants were either given a foliar application of 40 g Mo ha^‐1, or an addition of N fertilizer (20 kg ha^‐1 at planting and/or 30 kg ha^‐1 as a side dressing), or inoculated with two selected Rhizobium strains. Nodulation parameters of common bean (cv. Ouro Negro 1992) were measured. At both sites, Mo application at 25 days after plant emergence decreased nodule number per plant, while nodule weight was not affected in Viçosa and was increased in Coimbra at 46 days after plant emergence. However, N application at planting decreased the number and the weight of nodules at both sites, while N side dressed did not affect nodule number or weight. Therefore, the main effect of Mo fertilization was an increase in the size of nodules. The main effect of Mo on nodulation appears to be the avoidance of nodule senescence, and so maintaining a longer period of effective N₂ fixation.