Nitrogen fixation in soybeans (Glycine max (L.). Merril): influence of the application of calcium to the soil and molybdenum applied in seed's pellet

Abstract

In the present paper pelleting of soybean seeds with rockphosphate containing three levels of molibdenum were studied with and without application of calcium sulphate in relation to nodulation, nitrogen fixation and manganese absorption by soybeans, in a greenhouse experiment. The experimental design was in complete randomized blocks with four replicates and the following treatments: No pellet; pellet with rockphosphate; pellet with rockphosphate and 0.0012 mg Mo/seed; pellet with rockphosphate and 0,0024 mg Mo/seed. All these treatments were repeated with and without 60 ppm of calcium added as sulphate to the soil. The experiment was carried out in a gray hydromorphic soil with manganese toxicity. While mean nodule weight was not affected by any of the treatments, total nodule weight was higher when calcium was applied or when the seeds were pelleted with rockphosphate in the pots without calcium. Molybdenum also decreased nodule weight in the absence of calcium. The highest values of total plant nitrogen were found in the treatments with molybdenum and calcium but highest nitrogen contents were observed in the pots with molybdenum but without calcium. Calcium increased manganese uptake by the plants probably due to the decrease of the pH as a result of liberation of SO₄ radicals. The high manganese levels in the plants (1100 ppm) did not seem to inhibit plant growth, it rather became apparent that calcium deficiency but not high manganese levels were the limiting factor of plant growth. Finally it was observed that seed pelleting with rockphosphate increased plant growth as measured by plant dry weight confirming the necessity of the application of calcium or seed pelleting in this soil to eliminate calcium deficiency.