Tillage and Residue Management Effects On Nitrous Oxide Emission From Sandy Loam Soil.

Mixed responses of soil nitrous oxide (N₂O) fluxes to reduced tillage/no-till are widely reported across soil types and regions. In a field experiment on a Danish sandy loam soil we compared N₂O emissions during winter barley growth following five years of direct drilling (DD) and reduced tillage (RT) with conventional tillage (CT). Each of these tillage treatments further varied in respect to whether the resulting plot crop residues were retained (+residue) or removed (-residue). Sampling took place from autumn 2007 to the end of spring 2008. Overall, N₂O  emissions were 27 and 26% lower in DD and RT, respectively, relative to N₂O emissions from CT plots (P<0.05). We observed that in residue removal scenarios N₂O emissions were similar for all tillage treatments, but in residue retention scenarios, N₂O emissions were significantly higher in CT than in either DD or RT (P<0.05). Irrespective of residue management, N₂O emissions from DD and RT plots never exceeded emissions from CT plots. Retention of residue was estimated to decrease emissions from the DD plots by 39% and in the RT plots by 9%, but increased N₂O emissions from the CT plots by 35%. Relative soil gas diffusivity (Rdiff), soil NO₃-N, soil temperature, tillage and residue were important driving factors for N₂O emission (P<0.05). A multiple linear regression model using Rdiff to represent the water factor explained N₂O emissions better than a water filled pore space (WFPS) based model, suggesting a need for review of current use of WFPS in N₂O prediction models. We conclude that in this Danish sandy loam soil with a five-year history of tillage treatments, DD did not increase N₂O emissions and that Rdiff based models could predict N₂O emissions better than WFPS based models.