Effect of soil tillage and N fertilization on NO mitigation in maize in the Brazilian Cerrado.

The management system of soils and nitrogen application can cause impacts on the NO emissions produced by the agricultural sector. In the establishment of practices of greenhouse gas mitigation for this sector, the objective of this study was to evaluate the effect of soil tillage, with and without N fertilization, on NO emissions from Oxisols under rainfed maize in the Brazilian Cerrado region. The managements were of monoculture maize under conventional tillage (CT) and no-tillage (NT), with (1) and without (0) application of N fertilizer (0 and 257 kg N ha). From November 2014 to October 2015, gas emissions were measured. The soil and climate variables were measured and related to the NO fluxes. In the N-fertilized treatments, NO fluxes were higher (P < 0.01), ranging from -21 μg m h to 548 μg m h NO under conventional tillage and from -21 μg m h to 380 μg m h NO under no-tillage, compared with -6 to 93 μg m h NO from systems without N application. There was a combined effect of mineral N and water-filled pore space for most NO fluxes. The emission factors of NO during maize cultivation were lower than the standard factor (1%) established by the International Panel of Climate Change. During the plant crop cycle, 30% less NO was emitted from the N-fertilized no-tillage than from the conventional tillage. For the total cumulative NO (crop cycle + fallow), the NO emissions from NT1 and CT1 were not different, but 10× higher than those from the respective crops without N fertilization. To the emissions per unit of grain yield, CT1 and NT1 emitted 769 and 391 mg NO kg grain produced, respectively, and NT1 was most efficient in fertilizer-into-product conversion. Under maize cultivation, the soil acted as NO source, regardless of the management.