Efeito da adubação nitrogenada em cobertura sobre o conteúdo de molibdênio da semente de feijão-caupi cultivado em solos coesos de baixa fertilidade natural

Abstract

In the literature, there are few studies that have evaluated the effects of nitrogen (N) on coverage on molybdenum (Mo) content in cowpea seeds. Our hypothesis is that N fertilization in top dressing increases the Mo content in cowpea seeds. A trial was conducted in São Luís, Maranhão, between May and August 2019. The treatments were arranged in a 4 x 2 factorial scheme: doses of Mo applied to the foliage (0, 50, 250 or 500 g ha-1) and N doses in top dressing (0 or 50 kg ha-1), in a block design randomized, with four replications. The Mo source was sodium molybdate and the N source was urea. At planting, all plots received 350 kg ha-1 of the 4-14-8 formula. It was used the cultivar BRS Guariba. The average productivity of the trial was 627±172 kg ha-1, and the plants that not receiving N or Mo presented 2.42±0.68 nodules per plant. There was interaction significant (P < 0.010) between doses of Mo and doses of N in productivity and Mo content in the seed. Without application of N in top dressing, productivity increased by 306 kg ha-1 (without Mo) to 729 kg ha-1 (with 250 g ha-1 of Mo). With application of N in coverage, there was no significant difference between the productivity obtained with doses between 50 and 500 g ha-1 of Mo, but plants sprayed with 50 g ha-1 of Mo produced 58% more grains than those without received Mo. Without application of N in top dressing, the Mo content in the seed increased until the dose of 500 g ha-1 of Mo and reached 5.9 μg seed-1 of Mo. With application of N in coverage, the Mo content in the seed increased up to the dose of 250 g ha-1 of Mo and reached 5.1 μg seed- 1 of Mo. Our results suggest that the application of N in top dressing increases the N content Mo in the seed when cowpea plants are sprayed with doses of up to 250 g ha- 1 of Mo.