Three series of experiments were carried out. In the first, the effects of N, Mo, and rhizobium were studied at two municipalities; in the second, conducted at another municipality, a factorial with four rates of N (0, 30, 60, and 90 kg ha-1) and four rates of Mo (0, 40, 80, and 120 g ha-1) was studied; and in the third, at six municipalities, the following combinations of N at planting time (kg ha-1), N as side dressing (kg ha-1) and Mo (g ha-1) were used, respectively: 0-0-0, 0-40-70, 20-0-70, and 20-40-70. In all experiments, Mo (as foliar spray) and N (as side dressing) were applied at about 25 days after plant emergence. Ordinary superphosphate (90 kg ha-1 of P2O5) plus potassium chloride (60 kg ha-1 of K2O) were applied as uniform fertilization for all experiments. The soils were contaminated by native strains of Rhizobium. Inoculation with selected strains of Rhizobium had no effect on grain yield. Molybdenum fertilization increased bean yield, and maximum yields were attained with 70 to 100 g ha-1 of Mo, depending on N fertilization: smaller rate of Mo was needed when greater dose of N was used and vice versa. Nitrogen applied at planting time was also essential and its absence could not generally be compensated by side dressing application. The N + Mo combination increased bean yield in approximately 90 to 200%.
Phaseolus vulgaris; nitrogen; molybdenum; Rhizobium