Bovine urine and dung deposited on Brazilian savannah pastures contribute differently to direct and indirect soil nitrous oxide emissions

Abstract

Cattle ranching is one of the most important agricultural activities in Brazil. The impact of livestock on soil N2O emissions in Brazil has only been assessed using a Tier 1 approach of the IPCC guidelines, as there are no data available from field studies. Apart from the need for accumulating data for the development of proper direct N2O emission factors, we tested for possible differences between urine and dung as N2O sources and the difference in emissions between the dry and wet season. An area of Brachiaria brizantha at the Embrapa Rice and Bean Centre in the Cerrado (central savannah) region (Goiás state) was subdivided into plots where fresh cattle urine and dung were monitored for three consecutive periods (two in the rainy and one in the dry season) for N losses, principally N2O emissions and NH3 volatilization. 15N-labelled urine N was used in the first monitoring period for an N balance study which indicated that denitrification and NH3 volatilization were the most important processes for N loss. Percentages of N lost as N2O and as volatilized NH3 were greater for urine than for dung. In addition, N losses as N2O in the rainy season were much greater than during the dry season. Representing the Cerrado region and the extensive pasture systems common in this region, direct emission 0.007gN2O–Ng−1 (0.7%) excreta N, well below the EF3PRP of 0.020gNg−1 (2%) used by IPCC for cattle N in excreta. The fraction of excreta N lost as NH3 of ∼15% was in line with the IPCC guidelines. Disaggregation of emission factors for excreta type is recommended.