Efeitos da densidade de plantas no enriquecimento dos grãos do feijão-mungo-verde com zinco

Abstract

In Maranhão, family farmers consider legumes, mainly beans, as a viable option, as is the case with the cultivation of mung bean (Vigna radiata L.). Because it is a little-known crop in Maranhão, it is necessary to develop technologies and management practices appropriate to the cultivation of the species. Our hypothesis is that increasing plant density and applying zinc (Zn) in the planting furrow and on the foliage of mung bean increases the Zn content in the grains and productivity. Our objective was to evaluate the combined effects of plant densities and levels of Zn applied in the planting furrow and on the foliage on grain productivity and the enrichment of mung bean grains with Zn. Two field trials were conducted, one in São Luís/MA and the other in Chapadinha/MA. The treatments were arranged in a factorial scheme (4 x 2): plant densities (8, 12, 16 or 20 plants/m), and levels of Zn applied in the planting furrow and on the foliage (0 or 9 kg/ha of Zn). A randomized block design was used, with four replications. The Camaleão cultivar was used. The following were analyzed: emergence, initial stand, beginning of flowering, appearance of the first mature pod, plant height, leaf area index, dry shoot mass, dry root mass, dry plant mass, N content in the leaves, grain yield, harvest index and Zn content in the grains. The average Zn content in the grains of plants that received Zn was 17% higher than the average Zn content in the grains of plants that did not receive Zn. With Zn, plant densities did not influence productivity (average = 926 kg ha-1). Without Zn, the average productivity at densities of 12 and 16 plants/m was 31.7% higher than the average productivity at a density of 8 plants/m. At a density of 8 plants/m, Zn increased productivity by 18.6% compared to the control. Our results suggest that, in mung bean cultivation in Maranhão, the application of 9 kg/ha of Zn applied to the soil and foliage is sufficient to enrich the grains with Zn, regardless of plant density. To maximize the productivity of mung bean grains, our results suggest that farmers can use a density of 8 plants/m with Zn fertilization in the soil and foliage or use densities of 12 and 16 plants/m without Zn fertilization.