Nitrous oxide (N2O) emissions in Savanah agrosystems

In Brazil, 87% of N2O released into the atmosphere comes from agriculture, emphasizing the importance of assessing emissions in agricultural systems. The aim of this study was to evaluate N2O fluxes and emissions in agroecosystems and to identify how physical and chemical attributes of soil may affect the emissions. The study was carried out in the northeastern savannah (Cerrado), in an area under current agricultural expansion, in the municipality of Bom Jesus, State of Piauí. The treatments were composed of grain cultivation systems under no-tillage: exclusive soybean with biological nitrogen fixation (FBN), exclusive corn and corn intercropped with brachiaria. An adjacent area under native Cerrado was evaluated as reference ecosystem. N2O fluxes were monitored using manual static chambers between February 18 and April 22, 2017, covering the period from planting until the beginning of the harvest. Corn cultivation systems presented the highest N2O fluxes and the highest total emissions. Nitrogen fertilization significantly contributed to soil N2O fluxes as opposed to FBN. The soybean system and the native Cerrado had the lowest N2O emissions. Substantial amounts of N2O may be emitted during plant residue decomposition, however, it was not evaluated in this study. The concentrations of NH4+ and NO3-available in the soil were different among the cropping systems, presenting a positive correlation with N2O fluxes.