THE EFFECT OF DIFFERENT MOISTURE REGIMES AND SOIL CHARACTERISTICS ON NITROUS-OXIDE EMISSION AND CONSUMPTION BY DIFFERENT SOILS

The emission and consumption of N2O by 18 soils having a wide variety of soil characteristics were determined in the laboratory during a 20- day incubation at three different moisture regimes: field capacity, sa turation, and waterlogged conditions. The highest N2O production and c onsumption occurred under saturated conditions, confirming that condit ions developing marginal anaerobic conditions, favor N2O accumulation. Furthermore, it indicates that, in the 18 soils tested, the N2O emiss ion was not primarily determined by the process rate, but by the relat ive N2O production, which is the percentage of reduced (denitrificatio n: N2O100/[N2O + N2]) or oxidized (nitrification: N2O*100/[NO2- + N2O ]) substrate being transformed into N2O. Multiple regression analysis with stepwise selection of variables showed that soil pH was the soil characteristic with the highest predictive value of the emission and m aximum concentration of N2O, probably through its direct effect on nit rification and denitrification. Other important characteristics were C aCO3 and sand content, having an effect on the diffusion characteristi cs of the soil, and the NO2- concentration before the experiment, whos e effect remains to be explained. The lack of predictive value of orga nic matter, water soluble organic matter, NO3- and NH4+ concentration may indicate that those factors were not limiting N2O emission or cons umption in most soils.