Índices fisiológicos e econômicos do milho sob níveis de água, nitrogênio e épocas de cultivo.

Abstract

The use of agricultural techniques such as irrigation and fertilization promote physiological responses capable of significantly altering the growth, development and yield of maize, but should be used in economically viable quantities. Thus, the objective of this work was to evaluate the physiological and economic indexes of this crop submitted to water and nitrogen (N) levels. The experiment was conducted in two seasons (spring/summer and autumn/winter) in the Rio Largo region, with 20 treatments and four replications. The maize was submitted to five irrigation levels (40, 80, 120, 160 and 200% of ETc) and four doses of nitrogen fertilization (0, 75, 150, 225 kg ha-1 of N). The crop was drip irrigated and the costs of irrigation and nitrogen fertilizer more the sale price of maize sack were used to determine the economic level of water and N. The physiological rates, biometric characteristics of the crop, chlorophyll and dry matter, as well as grain yield. As a result, it was observed in the autumn-winter period the maize has lower water requirement and lower grain yield than in the spring-summer period. In the latter period there is greater significance in the physiological responses of the plant to treatments such as greater stomatal condutance and greater transpiration, allied to higher photosynthetic rates. The maximum yield of maize grains in crops in rainy and dry seasons can be obtained with nitrogen doses equal to 156 kg ha-1 and above the 225 kg ha-1, respectively. In the dry season, the maximum yield can be obtained with irrigation level equivalent to 164% of ETc. Depending on input prices and grain sales, the nitrogen dose of maximum economic efficiency for the rainy season is of the order of 93 kg ha-1, while for the dry period it is around 200 kg ha-1; for the spring-summer crop, the maximum economic irrigation level corresponds to 96% of the ETc.