EFFECT OF AMMONIUM AND NITRATE APPLICATION ON THE NO AND N2O EMISSIONOUT OF DIFFERENT SOILS

The effect of nitrate and ammonium application (0, 50, 100 and 150 mg N kg(-1) soil) was studied in an incubation experiment. Four Belgian s oils, selected for different soil characteristics, were used. The appl ication of both nitrate and ammonium caused an increase of the NO and N2O emission. The NO production from nitrate and ammonium was found to be of the same order of magnitude. At low pH the NO production was fo und to be highest from nitrate, at higher pH values the production was found to be higher from ammonium. This seems to be the result of the negative effect of low pH on nitrification. The ANOVA analysis was car ried out to separate the effect of the form of nitrogen, quantity of N applied and soil characteristics. The total production of NO was foun d to depend for 97% on the soil characteristics and for 3% on the quan tity of N added. The total N2O production depended for 100% on the soi l characteristics. Stepwise regression analysis showed that the total NO production was best predicted by a combination of the factors CaCO3 content and NH4+ concentration in the soil. Total N2O production was best described by a combination of CaCO3, water soluble carbon (WSC) a nd sand-content. The N2O/NO ratio was found to be highly variable, ind icating that their productions react differently to changes in conditi ons, or are partly independent. It may be concluded that to NO and N2O from soils both nitrification and denitrification may be equally impo rtant, their relative importance depending on local conditions such as substrate availability, water content of the soil etc. However, the N O production seems to be more nitrification dependent than the N2O pro duction.