Strategies to Reduce N2Ο Emission From No-till Systems: Measurement and Modeling.

Agricultural soils and the application of N fertilizer account for about 24% of the global annual N₂O emissions. Modeling has been adopted in research for interpreting and synthesizing field observations, as well as predicting impacts of tillage on N₂O fluxes. The objectives of this study were to 1) assess N₂O emissions from different N management strategies under long term (LT) and short term (ST) no-till (NT) system; 2) test DNDC model for N management.  Nitrous oxide emissions were evaluated since summer of 2008 on a Kennebec silt loam. Three management strategies were evaluated in LT; 1) Fertilizer type: manure (M), urea (F), and slow release N fertilizer (SRNF); 2) N placements: broadcast (BC), surface banded (SB) and subsurface banded (SUB) and 3) Split application of Urea (SU).  Three fertilizer placements (BC, SB, and SUB), SRNF, and SU were evaluated in the ST. The results were statistically analyzed using Proc Mixed from SAS.  For the LT study N₂O-N emissions were not significantly different between tillage systems and N source. The cumulative N values of N₂O-N were greater in the tilled (T) than the NT system (2.7 kg N₂O-N/ha/y and 2.4 kg/ha/y, 3-y average). The cumulative emission of F and M N-source were 3.7 and 1.4 kg N₂O-N/ha/y, respectively.  Overall, there were no significant differences among the placement treatments. SB had the highest N₂O-N cumulative emissions (6.4 kg/ha/y 2-y average) which was higher than the BC N application on the LT (2.5 kg N₂O-N/ha/y, 3 y average). During 2010, SRNF had low emissions than SB and SU. Similarly, under the ST, the treatments BC, SUB, SB, SU and SRNF were not significantly different  (2.2, 1.9, 1.6, 1.6 and 1.6  kg/ha/y 3-y average, except for SUB, SU and SRNF, respectively), which were higher than  Control (0.2 kg N₂O-N kg/ha/y 3-y average). Emissions from LT no-tillage were statistically similar to tilled systems, although tilled presented higher cumulative values. Banded application of N enhanced the N₂O-N flux in LT no-till systems, which was not significant in ST. SRNF reduced the emissions but it was not significantly different neither from ST no-till system nor LT.