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The within-field variability of soil mineral nitrogen (N-min) in a grazed grassland of 8000 m(2) was examined. NO3--N concentrations were characterized by a high spatial variability. This can be explained by the uneven deposition of animal excreta. All NH4+-N as well as NO3--N values were lognormally distributed, be fore and after the grazing season. At the end of the grazing season the largest part of the variability of NO3--N was found for NO3--N concentrations measured within a distance of a few metres. A high variability for NO3--N over very short distances was also indicated by a large nugget variance. During the grazing season, observed mean N-mn, values increased from 22 to 132 kg N ha(-1). Regions with clearly higher NO3--N concentrations could be identified. These zones matched with the drinking place and the entrance of the pasture, places which were more frequently visited than others. High residual N levels in autumn led to relatively high losses of N, mostly by leaching, during the subsequent drainage period. Knowing the variability of N-min, the number of samples needed to estimate the average N-min in a field could be calculated for different probabilities and various degrees of precision. From the spatial distribution of the N-min concentrations and the restrictions imposed by the new European decree, adapted fertilizer strategies can be proposed at least for places where systematically higher N-min concentrations can be expected

N20 emissions and denitrification N‐losses. precipitation, air temperature, soil moisture, bulk density and content of mineral N were monitored in 9 different agricultural soils in 6 European countries throughout the vegetation period (April to September) 1992 and 1993. N2O emissions and denitrification N‐losses were log‐normal distributed, reflecting high temporal changes. While small flux rates (< 2 g N ha−1 d−1) were detectable every day, high rates (> 10 g N ha−1 d−1) were measured after fertilization. An attempt to relate the emission variables to climate and soil variables was made through the use of correlation analysis. The mean N20 emissions from soil were significantly correlated with the soil properties clay, organic C and mineral N content and the amount of applied mineral N fertilizer. The best prediction of the N2O emission rates (r2 = 0.734) was achieved by multiple linear regression using the soil parameter clay and mineral N. Only 50% of the observed variation could be explained by the factors Corg and mineral N, which describe the substrate availability for microbial processes. No successful statistical model was found for the prediction of denitrification N‐losses.

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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 soils, selected for different soil characteristics, were used. The application of both nitrate and ammonium caused an increase of the NO and N20 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 found 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 carried out to separate the effect of the form of nitrogen, quantity of N applied and soil characteristics. The total production of NO was found to depend for 97% on the soil characteristics and for 3% on the quantity of N added. The total N20 production depended for 100% on the soil characteristics.Stepwise regression analysis showed that the total NO production was best predicted by a combination of the factors CaCO3 content and NH + concentration in the soil. Total N20 production was best described by a combination of CaCO3, water soluble carbon (WSC) and sand-content.The N20/NO ratio was found to be highly variable, indicating that their productions react differently to changes in conditions, or are partly independent.It may be concluded that to NO and N20 from soils both nitrification and denitrification may be equally important, their relative importance depending on local conditions such as substrate availability, water content of the soil etc. However, the NO production seems to be more nitrification dependent than the N20 production.

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