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 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^?1, 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^?1 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^?1 OD soil h^?1, and a peak N₂O flux of 0.002 μmol N g^?1 OD soil h^?1 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.