N2O and N-2 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 (N-2) emissions as they receive regular inputs of N from various sources. To understand the factors affecting N2O and N-2 emissions and their ratio as influenced by soil amendments (zeolite or lime), we conducted laboratory experiments using 10-L plastic containers at 25 degrees C for 28 days. Soil samples (0-0.1 m soil depth) collected from pasture and adjacent wetland sites were treated with nitrate-N (NO3-) at 200 kg N/ha with and without added lime or zeolite. Nitrous oxide and N-2 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 N-2 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 N-2 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 N-2 emissions and lower N2O:N-2 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 N-2, 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.