Estoques de C e N e emissões de óxido nitroso sob cobertura vegetal de pastagem de Brachiaria brizantha e mata, em Itabela (BA)

Abstract

The atmospheric concentration of greenhouse gases (GHG) such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) has increased significantly since the Industrial Revolution and agriculture contributes more significantly to this increase. Entratanto, some management practices favor the increase in stocks of C and N in the soil and are of great importance to mitigate global warming. The overall objective of the study was to verify emissions of nitrous oxide and carbon and nitrogen stocks in areas under Brachiaria spp pastures to soil and climatic conditions Itabela, South Bahia. Two experiments were done. The first experiment was evaluated the stock of C and N in two transects in areas established to fifteen years with productive Brachiaria brizantha cv Arapoti and Brachiaria brizantha cv Xaraés and native forest in the Animal Science Experimental Station (CEPLAC) Itabela- Bahia. The experimental design was completely randomized with four replications for each treatment. Trenches were opened where soil samples were collected up to 100 cm deep for the determination of bulk density, carbon, nitrogen, δ13C and light fraction of SOM. The highest levels of carbon and nitrogen, the stock of C and N in the soil were observed in the areas under pasture. The carbon contribution derived from pastatagens (C4) was higher only in the first 5 cm of soil. The free light fraction intake was higher in the surface (0- 10 cm) for both treatments, and pastures showed higher FLL input regarding the forest, where there is greater input and accumulation of plant biomass. The second experiment evaluated the effect of bovine excreta originating from dairy cows that pastejavam in consortium areas (Brachiaria and legume Desmodium ovalifolium) and areas of monoculture (Brachiaria) and the effect of the application of nitrogenous fertilizers (urea) in an area B. brizantha cv Marandu from under the nitrogen gas losses. 36 plots were established in an experimental design of 6 randomized blocks with six treatments (urea, monoculture urine, urine consortium, monoculture feces, feces consortium and control), in two periods of application of excreta (dry and wet. The sampling gas (N2O) were made by the method of closed static chamber. comitantly held soil sampling for verification of soil moisture, the pore space saturated by water (EPSA), levels of nitrate, ammonium in the soil and soluble carbon, and volatilization ammonia. the deposition of excreta in pasture under significantly increased the flow of nitrous soil oxide and volatilized ammonia, compared to the control. in the rainy season these flows were associated with the availability of nitrate in soil and pore space saturated with water. in dry season, the nitrous oxide flows were associated with levels of nitrate and soil carbon urine was the treatment that provides higher losses of nitrogen in areas pastagem. The accumulation of N2O in treatments consortium urine showed higher in the dry season. The biggest losses by ammonia volatilization occurred in the rainy season.