Efeito de doses de nitrogênio na produção de forragem e de grãos de genótipos de milho sob condições de superadensamento

Abstract

With production in the 2015/2016 harvest of approximately 67 million tons and yield of 4.2 t.ha-1, corn (Zea mays L.) is one of the most produced grains in Brazil. In Alagoas, the cultivation of this culture is highlighted in the mesoregions agreste and sertão of the state. The crops production is directly linked to the genetic potential of the variety and its managing practices, among them, the seeding density and the soil fertility are indispensable in reaching higher crop yields. And so, the intent with this paper was to analyze the effect of applying four nitrogen doses and the efficiency and use of this nutrient on three distinct grain genotypes, grown under overwhelming forage and grain production densification conditions, in Rio Largo´s County, in Alagoas. The experiment was conducted at the Agricultural Sciences Center of the Federal University of Alagoas (CECA / UFAL). Two groups of treatments were evaluated: Group 1 - Corn genotypes (Viçosense, Branca and Nordestino), from the Plant Genetic Improvement Sector of CECA / UFAL; And Group 2 - Nitrogen doses (80, 160, 240 and 320 kg.ha- 1), the source being urea. The experimental design was a randomized complete block and factorial scheme (3x4), three grain genotypes and four nitrogen doses, with three replicates. In all blocks, the plants were over-weighted, with 0.6 m between rows and 0.2 m between plants in the row, with two plants per hole, which guaranteed a density of approximately 166,667 plants per hectare. The following characteristics were evaluated: forage production and its qualitative characteristics (dry matter, mineral matter, nitrogen, crude protein, neutral detergent fiber, acid detergent fiber, hemicellulose and crude fiber), grain yield and cob characteristics (cob weight with and without straw, cob length with and without straw, and cobs diameter with and without straw). For genotypes whose interaction characters G x N were not significant at 5% probability, and the genotypes with each nitrogen dosage for interaction characters G x N were not significant at 5% probability, Tukey test was applied at 5% probability in order to obtain the comparisons average; As well as the polynomial regression and a determining coefficient were applied to obtain the average for the different nitrogen dosages which were not significant at 5% probability in the interaction characters G x N. In relation to the production of green matter (PFMV), the genotypes presented satisfactory performance, with a general average production of 54,288.11 kg.ha-¹. For grain yield (PG), the dosage of 320 kg.ha-¹ of nitrogen guaranteed a higher production for all genotypes evaluated. The choice of the genotype combined to the practice of nitrogen fertilization directly interferes with its productivity, whether it is to produce grain or forage production.