Carbon and carbon dioxide accumulation by marandu grass under nitrogen fertilization and irrigation¹

Acúmulo de carbono e dióxido de carbono pelo capim-marandu sob adubação nitrogenada e irrigação

ABSTRACT

Nitrogen (N) is the most limiting nutrient for growth of forage grasses, especially in conditions of low water availability. Therefore, it is important to evaluate the effect of N fertilization and irrigation on the accumulation of carbon (C) and carbon dioxide (CO₂) by marandu grass in the Cerrado Paulista, in the rainy and dry seasons. Experiments were conducted to evaluate N fertilization in each season, with and without irrigation. Five N rates were used (0, 50, 100, 150 and 200 kg ha^-1 per cutting), using urea as N source, totaling 0, 300, 600, 900 and 1200 kg ha^-1 in the rainy season and 0, 100, 200, 300 and 400 kg ha^-1 in the dry season. The experiments were arranged in a split-plot randomized block design. There was no significant interaction (p > 0.05) between N and time of fertilization in the irrigated experiment. However, N promoted a quadratic effect in organic matter production (OMP), accumulation of C and CO₂ by marandu grass, while there was no influence of the seasons. In the non-irrigated experiment, the interaction between N rates and seasons was significant (p < 0.05) only for the rainy season. Organic matter production and C and CO₂ accumulation was greater in the rainy season than in the dry season. Irrigation provided increases of approximately 20% in C and CO₂ accumulation. The use of N and irrigation increases the accumulation of C and CO₂ by marandu grass, and this increase is higher during the rainy season.

Keywords:
global warming; greenhouse effect; forage; Brachiaria brizantha cv Marandu