文摘
The antecedent effect of lime on the gaseous products of denitrification (N2O and N2) was examined in a laboratory study using a clay loam soil (Soil 1) with a starting pH of 5.4, and a sandy loam soil (Soil 2) with a starting pH of 5.3. The soils were amended with 0, 2.3, 5.7 and 18.9?g CaCO3 kg?, and were incubated for a period of 3?years at 4?°C during which time the soil equilibrated at pH values of 4.7, 5.8, 7.3 and 7.7 (Soil 1) and pH 4.7, 5.2, 6.6 and 7.6 (Soil 2). Ammonium nitrate, labelled with 15N (15NH4NO3, NH4 15NO3 and 15NH4 15NO3) was added to each incubation jar at a rate of 7.14?μmol?N?g? oven dried (OD) soil. Headspace gas samples were extracted daily over a 5?days incubation period at 20?°C. The amount of N2O and N2, and 15N enrichment of N2O-N in the headspace, was determined using continuous-flow isotope-ratio mass spectrometry. As pH increased, the quantity of N2 and N2O emitted significantly increased in both soils (P?<?0.001), with a peak N2 flux of 0.179?μmol?N?g? OD soil?h?, and a peak N2O flux of 0.002?μmol?N?g? OD soil?h? occurring at pH 7.6, 2?days after the addition of NH4NO3. The loss as N2 far exceeded the loss of N2O, which remained at less than 1?% of the total mineral N content of the soil. Lime generally lowered the N2O:N2 ratio, however the results from this study suggest that it is not a mitigation strategy for GHG emissions.