Cattle Slurry Affects Nitrous Oxide and Dinitrogen Emissions from Fertilizer Nitrate

Abstract

Readily decomposable C in organic manures could enhance denitrification of NO3 existing in soil. The worst scenario occurs when farmers apply manures and NO3‐containing fertilizers at the same time to meet the nutrient requirements of the next crop. If the denitrification produced N2O rather than N2, the emission factor of 1.25% of fertilizer N used to calculate national inventories for N2O would be an underestimate for this farming practice. We used the 15N gas–flux method to measure N2O and N2 fluxes from grassland when cattle slurry (CS) containing 60 kg NH4–N ha−1 and KNO3 (60 kg N ha−1) were applied at the same time. By labeling the KNO3 and the NH4 in CS, we quantified the processes producing N2O and checked for N2 production by microbial processes other than denitrification. On average over field experiments replicated in March, May, August, and September 1997, CS increased the flux of N2O by 0.63% of the applied NO3–N in the 104 h after application, but had no significant effect on the flux of N2 The maximum flux of N2O was always observed in the first measurement period (5–7 h) after CS application. All of the N2O was formed by reduction from NO3 apart from in August when 10% was formed by nitrification in the CS treatment. There was no evidence for production of N2 by other processes such as heterotrophic nitrifier denitrification or anaerobic NH4 oxidation.