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 maysL.)-wheat (Triticum aestivumL.) 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 (R-2=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.