Nitrous Oxide and Ammonia Emissions from N Fertilization of Maize in a Brazilian Midwest Oxisol.

The Brazilian Midwest region is responsible for more than 44% of corn (Zea mays L.) produced in the country. This crop is one of the largest consumers of syntetic N-fertilizers in Brazil, which is an agricultural practice of growing environmental concern as one important source of N₂O emission. In a field experiment we quantified N₂O emissions and NH₃ volatilization from surface-applied fertilizers on maize crop under center pivot in the Brazilian savannah in a clayly Oxisol. We used three fertilizers at the rate of 150 kg N ha^-1 splitted into two topdressings-N (40 kg N ha^-1 at V1-V2 and 110 kg N ha^-1 at V4-V6 growth stage), which were: calcium ammonium nitrate - CAN, urea, and ammonium sulfate, and a control (without N application). The treatments were arranged in a randomized block design with five replications. We found that the greatest N₂O emissions were concentrated in the first two weeks after application of fertilizers, with peaks between three and four days. Higher emissions were observed after the second fertilization due to the higher amount applied. The N₂O emissions, and particularly the emissions measured in the CAN fertilizer treatment, were clearly related to the N-NO₃^- availability in soil interacting with the very high water content (WFPS > 60%). The calcium ammonium nitrate showed the highest N₂O emission factor (0.84%), followed by urea (0.42%), and ammonium sulfate (0.41%).  Due to strong rainfall events (> 20 mm) less than 24 hours after fertilizer application, the cumulative N loss as volatilized NH₃ from urea was very low (2.7%) and significantly higher than ammonium sulfate, and CAN. The results show that at such conditions and production systems, N-fertilizers showed lower N₂O emissions than IPCC default emission factor (1%). No significant diferences among fertilizers were found for productivity.