Application of molybdenum and cobalt in soybean seeds

Molybdenum and Cobalt applied to seeds is a common practice of soybean cultivation in Brazil. A field experiment was carried out on a Clay Rhodic Hapludox soil, pH (0.01 mol L-1 CaCl2) 5.2, in Ponta Grossa, State of Paraná, Brazil, aiming to evaluate the effects of Mo and Co seed application on soybean nodulation, mineral nutrition, and grain yield. Seed treatments with Mo (0 and 48 g ha-1) and Co (0, 2, 4 and 8 g ha-1) were tested in randomized complete block, with four replications, in a 2 x 4 factorial scheme. No interaction occurred between the effects of the two elements. There was no effect of treatments on nodulation as the efficiency of N2 symbiotic fixation, evaluated by soybean N uptake, or content in leaf or grain. Molybdenum treatment decreased Fe content in the leaves but did not affect soybean yield. There was a significant linear decrease in plant height, leaf concentration of Zn, and grain yield proportional to the Co amount applied. The results showed that the application of Mo is not necessary in soil with pH (0.01 mol L-1 CaCl2) 5.2, and that Co applied to the seed at rates higher than 3.4 g ha-1 is toxic to the plant.

Glycine max (L.) Merrill; nodulation; symbiotic fixation; nitrogen; mineral nutrition