Reducing nitrous oxide emissions from a maize‐wheat sequence by decreasing soil nitrate concentration: effects of split application of pig slurry and dicyandiamide

Pig slurry (PS) is a valuable nitrogen (N) source for agricultural crops but the simultaneous supply of readily decomposable carbon and mineral N can result in large soil nitrous oxide (N₂O) emissions. Our objective was to determine the individual and combined effects of split PS application and addition of a nitrification inhibitor (dicyandiamide, DCD) on N₂O emissions and soil mineral N concentration in southern Brazil. Soil N₂O fluxes were measured from November 2010 to November 2011 from a maize (Zea mays L.)‐wheat (Triticum aestivum L.) sequence under various fertilizer treatments: no‐N control, PS applied in a single pre‐plant dose with or without DCD, PS split‐applied with or without DCD, and urea split‐applied. Cumulative N₂O emissions increased linearly (R² = 0.73) with increasing soil nitrate (NO₃^?) exposure, indicating that management practices aimed at reducing soil NO₃^? concentrations can decrease soil N₂O emissions. In total for the two crops, splitting PS reduced N₂O emission factors (EF) by 33%, whereas the addition of DCD reduced EF by 60 and 41% when PS was applied in single and split doses, respectively. However, splitting PS or adding DCD failed to reduce N₂O losses more than a single pre‐plant PS application in maize where background soil NO₃^? concentrations were large. The addition of DCD to PS applied as a single pre‐plant dose resulted in the largest reduction in soil N₂O emissions, whereas splitting PS with and without DCD resulted in significantly smaller abatements. Consequently, we concluded that adding DCD to PS in a single pre‐plant application is a better option than splitting PS applications for reducing soil N₂O emissions in no‐till cereal cropping systems in southern Brazil.