Respostas agronômicas de Brachiaria brizantha cv. Marandu e Panicum maximum cv. Mombaça em função do suprimento de nitrogênio e água

Abstract

Plant growth depends on factors linked to genetics and weather conditions which some factors are controllable, such as water and nutrient supply. The aim of this study was to determine the growth potential of two forage genotypes as function of nitrogen (N) and water supply and verify the physiological variations caused by lack or presence of N and water. The study was conducted at Animal Science Department of UFLA in Lavras, MG, from October 2015 to July 2016. Two identical experiments were conducted simultaneously and adjacent, one kept under rainfed and the other irrigated. In each experiment two cultivars (Brachiaria brizantha cv. Marandu and Panicum maximum cv. Mombaça) and two N doses (0 and 550 kg N ha -1 year -1 ). They were harvested every 28 days during Summer and 42 days in Winter, leaving a residue of 15 and 40 cm respectively. The experimental design was randomized complete blocks with three replications. In each harvest were measured forage accumulation, canopy height, leaf area index, leaf angles and a canopy light interception, as well as foliar photosynthesis and gas exchange rates. Forage mass in residue was evaluated in two cycles (summer and winter). Cultivars when cultivated without N produced 7900 kg DM ha -1 , and when cultivated with N apply, Mombasa produced more than 21000 kg DM ha -1 , being 51% more productive than Marandu. About nitrogen dose, Marandu and Mombasa grasses produced 62% and 189% more forage than zero N treatment, respectively. Photosynthesis varied according to cultivar and nitrogen doses alone, where Marandu photosynthesis was 14% higher than Mombasa and nitrogen fertilization promoted 19% increase in photosynthesis. Marandu residue mass where 8634 kg MS ha -1 accumulated about 31% more biomass than cultivar Mombasa even under lower cutting height. The residual biomass did not change with water supply. When fertilized and under rainfed system, forage achieve 8833 kg DM ha -1 , an increase of 38% related to the system without N. Cultivars responded differently to N supply and water.