N₂O and N₂ emissions from pasture and wetland soils with and without amendments of nitrate, lime and zeolite under laboratory condition

Pasture and wetland soils are regarded as the major source of nitrous oxide (N₂O) and dinitrogen (N₂) emissions as they receive regular inputs of N from various sources. To understand the factors affecting N₂O and N₂ emissions and their ratio as influenced by soil amendments (zeolite or lime), we conducted laboratory experiments using 10-L plastic containers at 25°C for 28 days. Soil samples (0-0.1m soil depth) collected from pasture and adjacent wetland sites were treated with nitrate-N (NO₃⁻) at 200kgN/ha with and without added lime or zeolite. Nitrous oxide and N₂ emissions were measured periodically from soil subsamples collected in 1-L gas jars using acetylene (C₂H₂) inhibition technique, and soil ammonium (NH₄⁺) and NO₃⁻ concentrations were determined to assess the changes in N transformation. Soil NO₃⁻-N disappeared relatively faster in wetland soil than that in pasture soil. In the presence of added NO₃⁻, wetland soils emitted significantly more N₂O and N₂ than pasture soils, while the reverse trend was observed in the absence of NO₃⁻. Total N₂O emitted as percentage of the applied N was 25% for wetland and 5.7% for pasture soils. Total N₂ emissions expressed as a percentage of the applied N from wetland and pasture soils were 5-9% and 0.29-0.74%, respectively. Higher N₂O and N₂ emissions and lower N₂O:N₂ ratios from wetland soils than pasture soils were probably due to the higher water content and greater availability of soluble C in wetland. Zeolite applied to wetland soils reduced N₂O emissions but had little effect on N₂O emissions from pasture soils. Liming appeared to exacerbate N₂O emissions from fertilised lands and treatment wetlands and shift the balance between N₂O and N₂, and may be considered as one of the potential management tools to reduce the amount of fertiliser N moving from pasture and wetland into waterways.