AMBIENT NITROUS-OXIDE EMISSIONS FROM DIFFERENT LANDFORM COMPLEXES AS AFFECTED BY SIMULATED RAINFALL

The response of ambient nitrous oxide (N2O) emissions to four levels of simulated rainfall (5, 10, 20, and 40 mm) was assessed using large-diameter cores of undisturbed soil in a greenhouse. The soil cores were taken from the two dominant soil-landform groups present in the study area: Mollic Albaqualfs in footslope complexes and Typic Haploborolls in shoulder complexes. The footslope complexes had higher ambient N2O emission than the shoulder complexes at all rainfall levels which was attributed to the differences in inherent characteristics of the soils occurring at these landscape positions. This demonstrates the importance of a spatially-based investigative approach to account for landscape-scale differences in soil characteristics when investigating N2O emission at a large scale. Rainfall level strongly influenced the aeration status of the soil which, in turn, affected N2O emission. Rainfall showed to be a potential suitable parameter in a predictive model for N2O emissions (R(2) = 0.73** and 0.57** on the footslope and shoulder complexes, respectively). Nitrous oxide emissions also occurred in bursts following high rainfall levels; major increases were observed following 20 and 40 mm rainfall. At these rainfall levels, the N2O fluxes from the footslope and shoulder complexes returned to the background level after 48 h and 24 h, respectively. In addition to an appropriate spatial sampling scheme, this study also illustrates the importance of rainfall in deriving a reliable temporal sampling scheme that would include rainfall-induced episodic emissions to obtain meaningful N2O flux estimates. The potential of using rainfall data for predicting N2O emission activity warrants further investigation under actual field condition.