Dynamics of trace gas production following compost and NO3− amendments to soil at different initial TOC/NO3− ratios

The influence of compost and NO3− amendments on the dynamics of denitrification was studied in a gas-flow soil core incubation system, which allows frequent measurements of NO, N2O, N2, O2 and CO2. Both a loam and a loamy sand were subjected to four treatments: (1) a control, (2) 100 kg ha−1 of NO3−-N, (3) 30 t ha−1 of compost, and (4) 100 kg ha−1 of NO3−-N and 30 t ha−1 of compost. In the loam, compost amendment increased the maximal N2O production rate, whereas NO3− availability prevented N2O consumption activity. The dynamics in the loamy sand were quite different and could be explained by enzyme kinetics and a high organic matter content. Cumulative denitrification was higher in the loam under all conditions, but due to a lower N2O/N2 ratio, the cumulative N2O production was always lower. The ratio of the initial TOC over the initial NO3− concentration of the soils was suggested as a guideline to keep N2O emissions from denitrification to a minimum. The simultaneous application of compost and NO3− yielded TOC/NO3− ratios below two, where N2O production was found to peak.