SPATIAL VARIABILITY OF NITROUS-OXIDE FLUXES AND CONTROLLING SOIL AND TOPOGRAPHIC PROPERTIES

Spatial heterogeneity of nitrous oxide (N2O) nux was characterized alo ng with various soil chemical, physical, and microtopographical proper ties to identify those determining flux in fertilized grassland in spr ing 1993 and in fertilized winter wheat in spring 1994. Measurements w ere made at random locations within regular grids, Nitrous oxide emiss ion was measured using closed chambers at 84 locations in each grid, s pread over 2 d. The ranges of emissions from the grassland and from th e winter wheat were 0 to 134 and 0 to 26.4 g N2O-N ha(-1)d(-1). Variog rams for N2O emission and for concentrations in the soil atmosphere at 100 mm depth indicated that spatial dependence was weak at both sites . Of the other properties, pH and nitrate showed weak autocorrelation but none of the soil physical properties showed any significant spatia l dependence. The results of multiple Linear regression suggested that denitrification was the main N2O production process at the grassland site, but nitrification may have been equally important at the drier w inter wheat site. At both sites, the highest N2O emissions were associ ated with areas of a few square centimeters to a few square meters, ly ing below the average slope. Use of a partial least squares regression technique to predict nitrous oxide flux revealed the contribution of air permeability in addition to nitrate, ammonium, and soil water cont ents. Our analyses suggested that nitrous oxide production, consumptio n, and transport processes varied markedly with depth (over a few cent imeters) near the soil surface.