Antecedent effect of lime on nitrous oxide and dinitrogen emissions from grassland soils

The antecedent effect of lime on the gaseous products of denitrification (N2O and N-2) 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(-1), and were incubated for a period of 3 years at 4 A degrees 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 N-15 ((NH4NO3)-N-15, NH4 (NO3)-N-15 and (NH4)-N-15 (NO3)-N-15) was added to each incubation jar at a rate of 7.14 mu mol N g(-1) oven dried (OD) soil. Headspace gas samples were extracted daily over a 5 days incubation period at 20 A degrees C. The amount of N2O and N-2, and N-15 enrichment of N2O-N in the headspace, was determined using continuous-flow isotope-ratio mass spectrometry. As pH increased, the quantity of N-2 and N2O emitted significantly increased in both soils (P < 0.001), with a peak N-2 flux of 0.179 mu mol N g(-1) OD soil h(-1), and a peak N2O flux of 0.002 mu mol N g(-1) OD soil h(-1) occurring at pH 7.6, 2 days after the addition of NH4NO3. The loss as N-2 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:N-2 ratio, however the results from this study suggest that it is not a mitigation strategy for GHG emissions.