A. Vermoesen

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, saturation, and waterlogged conditions. The highest N2O production and consumption occurred under saturated conditions, confirming that conditions developing marginal anaerobic conditions, favor N2O accumulation. Furthermore, it indicates that, in the 18 soils tested, the N2O emission was not primarily determined by the process rate, but by the relative N2O production, which is the percentage of reduced (denitrification: N2O*100/[N2O + N2]) or oxidized (nitrification: N2O*100/[N2O− + N2O]) substrate being transformed into N2O Multiple regression analysis with step-wise selection of variables showed that soil pH was the soil characteristic with the highest predictive value of the emission and maximum concentration of N2O, probably through its direct effect on nitrification and denitrification. Other important characteristics were CaCO3 and sand content, having an effect on the diffusion characteristics of the soil, and the NO2− concentration before the experiment, whose effect remains to be explained. The lack of predictive value of organic matter, water soluble organic matter, NO3− and NH4+ concentration may indicate that those factors were not limiting N2O emission or consumption in most soils

Progress in Nitrogen Cycling Studies

N research effort has undergone major changes over recent decades with changing emphasis because of environmental problems and issues. This driving force, coupled with a universal desire to improve N-use efficiency, appreciation of the importance of maintaining soil resource quality and a need to provide integrated landscape managements, will continue to prompt new research areas and issues for study. Already, much information has been provided and new approaches and needs defined. It will be essential in future research to take full note of the many interactions that occur and to provide a mechanistic basis so that scaling of effects can be undertaken with the appropriate simplification without being superficial. Examples of interactions, as well as fundamental gaps in the basic processes are discussed and needs for future research identified.

Effect of ammonium and nitrate application on the NO and N2O emission out 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 soils, selected for different soil characteristics, were used. The application 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 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, quantily 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 N2O 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 NH4+ concentration in the soil. Total N2O production was best described by a combination of CaCO3, water soluble carbon (WSC) and sand-content.The N2O/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 N2O 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 N2O production. ei]{gnE}{fnMerckx}{edSection editor}

Within-field variability of mineral nitrogen in grassland

Abstract The within-field variability of soil mineral nitrogen (Nmin) in a grazed grassland of 8000 m2 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, before 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 Nmin 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 Nmin, the number of samples needed to estimate the average Nmin in a field could be calculated for different probabilities and various degrees of precision. From the spatial distribution of the Nmin concentrations and the restrictions imposed by the new European decree, adapted fertilizer strategies can be proposed at least for places where systematically higher Nmin concentrations can be expected.

Nitrous Oxide Emission out of Grassland

Grazed grassland which received 295 kg ha−1 N-fertilizer (NH4NO3), split-applied, was used to measure nitrous oxide emission. The closed box method was used. At the same time, also soil cores were taken for incubation in the presence of acetylene. During 280 days in 1992, a total emission of 8.4 kg N2O-N ha−1 was found. This was close to 50 % of the total denitrification, which was 18.7 kg (N2O+N2)-N ha−1 over 280 days. A variability study on N2O emission was carried out on a surface of 1, 100 and 10,000 m2, respectively. This study confirmed the lognormal distribution of data with variation coefficients of 20 to 25%. It was also found that the effect of application of 200 kg KNO3-N on N2O emission was limited to 2 weeks upon fertilization. It more than doubled the emission rate during this period.

LABORATORY STUDY OF THE EMISSION OF N2O AND CH4 FROM A CALCAREOUS SOIL

The emission of N2O and CH4 from a calcareous soil was studied, in the laboratory, with the addition of inorganic N at different soil water levels. On the whole, the addition of NH+4 led to significantly higher N2O emissions than the addition of NO−3. At 2/3 and 1.5 times field capacity, the N2O production was caused mainly by nitrification. At 3 and 6 times field capacity, nitrification and denitrification produced N2O simultaneously, in spite of low nitrification rates. The highest N2O emission was obtained at the more intermediate soil water levels (1.5 and 3 times field capacity) at which marginal oxygen conditions are likely to occur rather than at the soil water levels that had the highest nitrification (2/3 field capacity) or denitrification (6 times field capacity) process rates. This indicates that the effect of O2 on the relative N2O production was more important in determining the N2O emission than the process rate. The C2H2 inhibition of the reduction of N2O to N2 failed at 6 times field capacity, probably because of insufficient C2H2 diffusion into the soil.

Long-term measurements of N2O emissions

Abstract Nitrous oxide (N 2 O) emission was measured weekly over a period of one year (1994) on a grassland, a maize field and a permanent pasture. Therefore, the closed box method was used. To estimate the total (N 2 O+N 2 ) loss, also soil cores were taken for incubation in the presence of acetylene. N 2 O fluxes were highest in the grazed grassland (11.9 kg N. −1 .435 days −1 ) because of the high nitrogen input (fertilization, deposition of urine and dung by cattle), a higher soil compaction and relatively high moisture content. N 2 O losses out of the temporary grassland (3.35 kg N.ha −1 .312 days −1 ) and maize field (2.7 kg N.ha −1 .312 days −1 ) were significantly lower. This is attributed to a lower N input and the fact that these 2 fields were very well managed (controlled fertilization, good drainage system, lower compaction,…). From an agronomic point of view, N-losses as N 2 O are small and not important to take into consideration. Besides, these small N 2 O fluxes can have a negative influence on the environment.

Laboratory Study of the Emission of NO and N2O from Some Belgian Soils

The NO, NO2 and N2O emission was measured, upon application of nitrate, ammonium and both, to four Belgian soils with different characteristics. The addition of NH4 + caused higher NO and N2O emissions than the addition of no nitrogen, or the addition of NO3 >−. In contrast to the two soils with a pH of approximately 8 the two soils with a pH around 6 showed a considerable delay in production of both NO and N2O upon the application of the ammonium, probably due to the lag-period of nitrification. The soils with a pH of 8 gave higher emissions on the application of NH4 + than the soils with a pH of 6. The emission of NO2 was found to be considerably lower than the NO emission from the soils. The NO/NO2 ratio varied between 5–25 at considerable NO emissions (>50 nmol kg−1). In the controls of soil 1 and soil 2, which showed very low NO emissions ratios of 50 nmol kg−1). Soil 3 and 4 gave lower N2O/NO ratios than soil 1 and 2. In the controls of soil 1 and soil 2, at low NO emissions, N2O/NO ratios of > 300 were observed. Soil 3 and 4 gave higher NO/NO2 and lower N2O/NO ratios than soil 1 and 2.

Emission of gaseous hydrocarbons and NH3 out of soils.

The biosphere, and soils in particular, interact importantly with the atmosphere. It was found that fertilisation with inorganic nitrogen (NH4 +, NO3 − and urea) contributes to the emission of NH3, NO and N2O. Field measurements of NO emission showed a clear diurnal fluctuation. The CaCO3 content and pH of the soil are important soil parameters controlling NH3, as well as NO and N2O emission. However, incorporation of the fertilisers into the soil instead of surface application can substantially reduce the NH3 emission.