Effect of liquid manure on the mole fraction of nitrous oxide evolved from soil containing nitrate.

The same emission factor is applied to fertiliser N and manure N when calculating national N2O inventories. Manures and fertilisers are often applied together to meet the N needs of the crop, but little is known about potential interactions leading to an increase in denitrification rate or a change in the composition of the end-products of denitrification. We used the 15N gas-flux method in a laboratory experiment to quantify the effect of liquid manure (LM) application on the fluxes of N2 and N2O when the soil contained fertiliser 15NO3-. LM increased the mole fraction of N2O from 0.5 to 0.85 in the first 12 h after application. More than 94% of the N2O was from the reduction of NO3-, probably due to aerobic nitrate respiration as well as respiratory denitrification.