Productivity of Marandu grass under irrigation levels and nitrogen levels in the Northeast of São Paulo

<p>The rational exploitation of pastures requires care, particularly for the supply of water and nutrients, mainly nitrogen, in a balanced proportion to the plants. The objective of this study was to quantify dry matter yield response (DM) of Brachiaria brizantha cv. Marand? to irrigation and nitrogen levels in Northern S?o Paulo State, Brazil, during spring and summer periods. The experiment was conducted from September 2015 to March 2016, in an area of 374 m², with plots of 6.2 m². The experiment was conducted in a split plot randomized block design with irrigation in the plot and nitrogen in the subplot, with four replications. Irrigation levels corresponded to a fraction of reference crop evapotranspiration, ETo (10%, 31%, 60%, 86% and 100%); N levels corresponded to the doses of N calculated on basis of DM productivity (7.5, 15 and 30 kg ha^{- 1} of N per ton of DM). The pasture was harvested at a height of 30 cm with 15 cm residue. Biomass yield was obtained by taking two random samples of 0.25 m² in each plot to make a composite sample. The results were subjected to analysis of variance and means were compared by Tukey test. DM in response to irrigation levels data were adjusted to a regression equation, with 5% significance level. During the experimental period, precipitation was 1,518 mm, evenly distributed, with 25?C average temperature. Despite high precipitation, a statistically significant difference was observed by the F test for the interaction N x irrigation levels. N doses of 15 and 30 kg ha^-1 led to higher DM equal to 22,428 and 22,414 kg ha^-1, respectively, which were superior to the dose of 7.5 kg ha^-1. DM yield in response to irrigation levels data were adjusted to a 4th degree regression function, significant at 5% and R² equal to 99%. The results showed that, despite the high precipitation, irrigation and nitrogen fertilization increased DM yield. Climate was found to be the factor of greatest importance on forage development by increasing nutrient absorption efficiency by plants. Despite high precipitation, it is likely that low radiation occurred during the rainy days had affected crop development, and thus response to the treatments was lower than expected.</p>