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Various models have been developed to determine ammonia (NH3) emissions from animal manure–processing lagoons to enable relatively simple estimations of emissions. These models allow estimation of actual emissions without intensive field measurements or “one‐size‐fits‐all” emission factors. Two mechanisms for lagoon NH3emissions exist: (a) diffusive gas exchange from the water surface and (b) mass‐flow (bubble transport) from NH3contained within the ebullition gas bubble (as it rises to the surface) produced from anaerobic decomposition of organic matter. The purpose of this research is to determine whether gas ebullition appreciably affects NH3emissions and therefore should be considered in emissions models. Specifically, NH3mass‐flow emissions were calculated and compared with calculated diffusive NH3emissions. Mass‐flow NH3emissions were evaluated based on a two‐film model, in connection with the acid dissociation constant of ammonium, to predict the degree of NH3gas saturation within the bubbles. Average daily ammoniacal nitrogen concentration, pH, and measured biological gas production (ebullition) in conjunction with literature values for Henry's law constant were used to calculate emissions from NH3saturation of ebullition gases. Ebullition enhancement of NH3surface emissions due to increased turbulence was estimated from average lagoon ebullition rates and literature values of turbulence enhancement. Ebullition enhancement of NH3surface emissions and ebullition mass‐flow NH3emissions was determined to be <10% and <0.052%, respectively, of total NH3emissions. Therefore, because ebullition effects are small, they may be neglected when developing process models to estimate NH3emissions from water surfaces of swine manure processing lagoons. Ammonia emissions models are used to estimate emissions from manure processing.Ebullition mass transport is insignificant compared with diffusion/turbulence emissions.Ebullition surface emission enhancement is less than the error of emission models.Biogas ebullition does not need to be included in ammonia emission models.

Apportionment of nitrate (NO3−) sources in surface water and classification of monitoring locations according to NO3−polluting activities may help implementation of water quality control measures. In this study, we (i) evaluated a Bayesian isotopic mixing model (stable isotope analysis in R [SIAR]) for NO3−source apportionment using 2 yr of δ15N‐NO3−and δ18O‐NO3−data from 29 locations within river basins in Flanders (Belgium) and five expert‐defined NO3−polluting activities, (ii) used the NO3−source contributions as input to an unsupervised learning algorithm (k‐means clustering) to reclassify sampling locations into NO3−polluting activities, and (iii) assessed if a decision tree model of physicochemical data could retrieve the isotope‐based and expert‐defined classifications. Based on the SIAR and δ11B results, manure/sewage was identified as a major NO3−source, whereas soil N, fertilizer NO3−, and NH4+in fertilizer and rain were intermediate sources and NO3−in precipitation was a minor source. The k‐means clustering algorithm allowed classification of NO3−polluting activities that corresponded well to the expert‐defined classifications. A decision tree model of physicochemical parameters allowed us to correctly classify 50 to 100% of the sampling locations as compared with the k‐means clustering approach. We suggest that NO3−polluting activities can be identified via clustering of NO3−source contributions from samples representing an entire river basin. Classification of future monitoring locations into these classes could use decision tree models based on physicochemical data. The latter approach holds a substantial degree of uncertainty but provides more inherent information for dedicated abatement strategies than monitoring of NO3−concentrations alone.

Total soil organiccarbon SOC stocks for grassland soils in Flanders N Belgium were determined for the Kyoto Protocol reference year 1990 and 2000 in order to investigate whether these soils have been CO2sinks or sources during that period. The stocks were calculated by means of detailed SOC datasets, which were available at the community scale for the whole of Flanders. The total SOC stocks for Flemish grassland soils 1 m depth were estimated at 38 Mt SOC in 1990 and 34 Mt SOC in 2000. The loss of SOC resulted from a decrease in the SOC content of grassland soils 71 and could also partly 29 be explained by a decline in grassland area. Significant decreases in SOC for the 0–6 cm depth layer were found for the 1990s for the coarsertextured soils with SOC losses ranging between –0.3 and –0.5 over the 10 y period. Specific management practices that disturb the SOC balance such as conversion to temporary grassland and a reduction of animalmanure application are hypothesized to have contributed to the observed loss of SOC stocks. We furthermore conducted an analysis of uncertainty of the 1990 and 2000 grassland SOC–stocks calculation using Monte Carlo analysis. Probabilitydistribution functions were determined for each of the inputs of the SOCstock calculation, enabling us to assess the uncertainty on the 1990 and 2000 SOC stocks. The frequency distributions of these simulated stocks both closely approached lognormal distributions, and their 95confidence intervals ranged between 150 and 50 of the calculated mean SOC stock. The standard error on the measured decrease in SOC stocks in Flemish grassland soils during the 1990s was calculated to be 7–8 Tg SOC, which is equivalent to twice this decrease. This clearly shows that largescale changes in SOC stocks are uncertaintyridden, even when they are based on detailed datasets.

Vermicompost is typically applied to improve soil quality, but can be used to remediate hydrocarbon-contaminated soils. Little information is available on how contamination and subsequent bioremediation with vermicompost affects emissions of N2O and CO2, important greenhouse gases. A sandy loam soil with different water contents (40%, 60%, 80% and 100% of water holding capacity (WHC)) was contaminated with phenanthrene, anthracene and benzo(a)pyrene and amended with or without vermicompost to stimulate remediation of soil. Emissions of N2O and CO2, and concentrations of inorganic N (ammonium (NH4+), nitrite (NO2−) and nitrate (NO3−)) were determined in a laboratory incubation experiment after 0h, 5h, 24h, 72h and 168h. The cumulative CO2production rate was significantly larger in soil incubated at 60%WHC and 80%WHC compared to soil incubated at 40% and 100%WHC. Addition of vermicompost increased production of CO2and N2O. Addition of PAHs increased production of CO2when water content of soil was at 60%WHC and production of N2O when water content of soil was at 80% WHC. Addition of PAHs induced immobilization of inorganic N and inhibited nitrification as the concentration of NH4+and NO2−in soil contaminated with PAHs was larger than in unamended soil while the concentration of NO3−was lower. It was found that contamination of soil with PAHs increased emissions of N2O and CO2and biostimulation of autochthonous microflora with organic material to remediate those soils further increases production of N2O and CO2. These findings indicate that trace gas emissions should be included in estimations of the environmental impact of contamination of soil and their subsequent bioremediation.

Following mineralization of N‐rich crop residues, large amounts of mineral N can be released into the soil. Manipulating N mineralization of crop residues may be an option to reduce NO3−in soil. The potential to manipulate the N release from vegetable crop residues by using organic wastes was tested under field conditions. At the start of the experiment, cauliflower (Brassica oleracea L. var. botrytisL.) residues (∼73 Mg fresh matter ha−1) together with an immobilizer waste (∼5 Mg C ha−1of straw, green waste compost, sawdust, or paper sludge) were incorporated into a silt loam soil. After 154 d, a remineralizing waste (∼1 Mg C ha−1of vinasse or dairy sludge) was incorporated. During the field experiment, the mineral N content in the soil was measured at regular time intervals, and net N release, NO3−leaching, and denitrification were simulated using a N mineralization–immobilization model coupled to a NO3−leaching model. Straw, green waste compost, and sawdust were able to immobilize between 54 and 68% of the N released by the cauliflower residues and reduced NO3−leaching by 56 to 68%. Paper sludge released an extra amount of N due to its low C/N ratio. No consistent remineralization of N could be found in any of the treatments, probably due to an unsuitable composition of the remineralizer wastes. Manipulating N release of N‐rich crop residues by using organic wastes may be a suitable method to reduce NO3−leaching; however, stimulating remineralization of immobilized N by the start of the following spring may not be easy to achieve.

The different management regimes on grassland soils were examined to determine the possibilities for improved and/or changed land management of grasslands in Flanders (Belgium), with respect to article 3.4 of the Kyoto Protocol. Grassland soils were sampled for soil organic carbon (SOC) and for bulk density.For all grasslands under agricultural use, grazing and mowing + grazing led to higher SOC stocks compared with mowing, and grazing had higher SOC stocks compared with mowing + grazing. Overall, 15.1 ± 4.9 kg OC m–2 for the clayey texture, 9.8 ± 3.0 kg OC m–2 for the silty texture, and 11.8 ± 3.8 kg OC m–2 for the sandy texture were found for grassland under agricultural use to a depth of 60 cm. For seminatural grasslands, different results were found. For both the clayey and silty texture, mowing and mowing + grazing led to higher SOC stocks compared with grazing. The clayey texture had a mean stock of 15.1 ± 6.6, the silty texture of 10.9 ± 3.0, and the sandy texture of 12.1 ± 3.9 kg OC m–2 (0–60 cm). Lower bulk densities were found under grazed agricultural grassland compared with mown grassland but for seminatural grassland, no clear trends for the bulk density were found. The best management option for maintaining or enhancing SOC stocks in agricultural grassland soils may be permanent grazed grassland. For seminatural grassland, no clear conclusions could be made. The water status of the sampled mown fields was influencing the results for the clayey texture.Overall, the mean SOC stock was decreasing in the order clay > sand > silt. The higher mean SOC concentrations found for the sandy texture, compared to the finer silty texture, may be explained by the historical land use of these soils.

Abstract Manipulating the N release from high-N crop residues by simultaneous mixing of these residues with organic biological waste (OBW) materials seems to be a possible method to reduce NO3− leaching. The aim of this study was to examine whether the incorporation of OBW materials together with a high-N crop residue (celery) had also an effect on N2O emission from horticultural soil under short-term and optimised laboratory conditions. A sandy loam soil and celery residues were mixed with different OBW materials and brought into PVC tubes at 80% water-filled pore space and 15°C. Every 2.5 h, a gas sample was taken and analysed by gas chromatography for its N2O concentration. The soil amended with only celery residues had a cumulative N2O emission of 9.6 mg N kg−1 soil in 50 h. When the celery residues were mixed with an OBW material, the N2O emission was each time lower than the emission from the celery-only treatment (between 3.8 and 5.9 mg N kg−1 soil during maximum 77 h), except with paper sludge (17.2 mg N kg−1 soil in 100 h). The higher N2O emission from the paper sludge treatment was probably due to its unusually low C:N ratio. Straw, green waste compost 1 (GWC1) and 2 (GWC2), saw dust, and tannic acid reduced the N2O emission of the celery treatment by 40 to 60%. Although the N2O reduction potential can be expected to be lower and with differing dynamics under field conditions, this study indicates that apart from reducing NO3− leaching, OBW application may at the same time reduce N2O emissions after incorporation of high-N crop residues.

Variations in 13C natural abundance and distribution of total C among five size and density fractions of soil organic matter, water soluble organic C (WSOC) and microbial biomass C (MBC) were investigated in the upper layer (0–20 cm) of a continuous grassland soil (CG, C3vegetation), a C3‐humus soil converted to continuous maize cultivation (CM, C4vegetation) and a C3‐humus soil converted to a rotation of maize cultivation and grassland (R). The amounts of WSOC and MBC were both significantly larger in the CG than in the CM and the R. In the three soils, WSOC was depleted while MBC was enriched in 13C as compared with whole soil C. The relative contributions to the total C content of C stored in the macro‐organic matter and in the size fraction 50–150 µm decreased with decreasing total C contents in the order CG > R > CM, while the relative contribution of C associated with the clay‐ and silt‐sized fraction <50 µm increased. This reflects a greater stability and physical protection against microbial degradation associated with soil disruption (tillage) of the clay‐ and silt‐associated organic C, in relation to the organic C in larger size fractions. The size and density fractions from the CG soil showed significant differences in 13C enrichment, indicating different degrees of microbial degradation and stability of soil organic C associated with physically different soil organic matter (SOM) fractions. δ13C analysis of the size and density fractions from CM and R soils reflected a decreasing turnover rate of soil organic C with increasing density among the macro‐organic matter fractions and with decreasing particle size. Copyright © 2002 John Wiley & Sons, Ltd.

Strategies used to reduce emissions of N2O and CH4in rice production normally include irrigation management and fertilization. To date, little information has been published on the measures that can simultaneously reduce both emissions. Effects of application of a urease inhibitor, hydroquinone (HQ), and a nitrification inhibitor, dicyandiamide (DCD) together with urea (U) on N2O and CH4emission from rice growing were studied in pot experiments. These fertilization treatments were carried out in the presence and absence of wheat straw, applied to the soil surface. Without wheat straw addition, in all treatments with inhibitor(s) the emission of N2O and CH4was significantly reduced, as compared with the treatment whereby only urea was applied (control). Especially for the U+HQ+DCD treatment, the total emission of N2O and CH4was about 1/3 and 1/2 of that in the control, respectively. In the presence of wheat straw, the total N2O emission from the U+HQ+DCD treatment was about 1/2 of that from the control. The total CH4emission was less influenced. Wheat straw addition, however, induced a substantial increase in emissions of N2O and CH4. Hence, simultaneous application of organic materials with a high C/N ratio and N-fertilizer (e.g. urea) is not a suitable method to reduce the N2O and CH4emission. Application of HQ+DCD together with urea seemed to improve the rice growth and to reduce both emissions. The NO3−-N content of the rice plants and denitrification of (NO3−+NO2−)-N might contribute to the N2O emission from flooded rice fields.

In vineyards, the long-term use of copper fungicides has increased soil Cu concentrations that can adversely affect the number and activities of soil microorganisms. To better understand this phenomenon and to ameliorate such harmful effects, an incubation experiment was carried out with a sandy loam and a sandy soil to which increasing rates of CuSO4were added. By this treatment, the basal soil respiration (7-55%) and decomposition of added vine branches (46-86%) was inhibited. At the application rate of 500 mg Cu kg−1, soil microbial biomass-C was inhibited (7-66%) in the sandy soil and stimulated (2-10%) in the sandy loam soil. The specific respiration rate was a reliable indicator for Cu stress, and it increased with time and higher Cu concentrations before lime and compost applications. Total number of bacteria and streptomycetes were also strongly inhibited. Fungal population was significantly more tolerant to copper toxicity than the bacteria. A stimulation of fungal population at a dose of 500 mg Cu kg−1in both soils was observed. A criterion such as “stimulation” lasting for more than 60 days can also be used as indication of Cu contamination of soils. The order of inhibition (on day 125) at a dose of 500 mg Cu kg−1soil was as follows: A. sandy loam soil (pH> 7.0) — fungi < biomass-C < basal soil respiration < bacteria < streptomycetes; B. sandy soil (pH< 6.0) — fungi < basal soil respiration < biomass-C < bacteria < streptomycetes. The application of lime increased soil recovering ability at a moderate rate (for CO2production – 22-70% and for biomass-C- 39-156%), but the combination of lime and compost significantly increased soil resiliency (for CO2production- 16-518% and for biomass-C- 103-693%). The soil resiliency assessed by number of bacteria in compost treatments was 30-120% in sandy loam soil and 92-700% in the sandy soil. Compost and lime application increased the number of streptomycetes from 52 to 500% in sandy loam soil and from 100 to 700% in sandy loam soil. Fungal population was less increased in sandy soil as compared to sandy loam soil. The ecological dose higher than 5% inhibition of microbial processes and microorganisms appears to be suitable to assess Cu contamination of soils. CO2production, biomass-C and specific respiration rate were less sensitive indicators as compared to streptomycetes and bacteria. It appears that compost application effectively promoted the recovery of soil microbial activity and soil fertility of Cu contaminated soils.

In this study N2O emissions from agriculture in Belgium have been split up per agro-pedological region and calculated per farm type. The N2O emissions were calculated according to the `Revised 1996 IPCC guidelines for national greenhouse gas inventories'. Input data were weighed averages of the N balance of a large number of farms per agro-pedological region and per farm type. As such, the input data represent a theoretical farm in each agro-pedological region and for each distinguished farm type. In a first part, N2O emissions were calculated for 10 agro-pedological regions in Belgium. The yearly N2O emissions varied between 225 and 462 kg N2O-N. The highest N2O emissions (around 400 kg N2O-N yr−1) were found in regions with fertile soils, dominated by crop production or a combination of crop production and cattle breeding. The lowest emissions (around 250 kg N2O-N yr−1) were found in regions with extensive cattle breeding. N2O emissions of 300 ± 15 kg N2O-N yr−1were found in regions with less extensive cattle breeding or in regions with combinations of cattle, pig and poultry breeding. The N2O emission per ha varied between 6 and 14 kg N2O-N yr−1. In a second part, N2O emissions were calculated for 12 different farm types. The yearly N2O emissions varied between 273 and 512 kg N2O-N. The highest emissions were found on farms with crop production or a combination of crop production and cattle breeding. The lowest emissions were found on farms specialised in only one activity of animal breeding. Specialised pig farms and farms with combinations of cattle caused the greatest threat with respect to N2O releases from agriculture. Their N2O emission per ha was 18–40 kg N2O-N yr−1, which was significantly higher than the average N2O release (10 kg N2O-N yr−1ha−1) for the other farm types.

According to the revised 1996 IPCC guidelines, several emission factors are needed to calculate national inventories of N2O emissions from agriculture. To estimate the direct N2O emissions from mineral soils, an emission factor of 0.0125 kg N2O-N per kg N applied is currently being used. From recent literature data it was clearly shown that real N2O emissions could differ substantially from this value. Based on the IPCC methodology an inventory of N2O emission from agriculture in Europe (EU-15) has been made. In 1996, the N2O emission was estimated at 672 Gg N2O-N. The N2O emission per country varied between 10 and 177 Gg N2O-N. The N2O emission per ha agricultural land in the various countries varied between 1.7 and 14.2 kg N2O-N ha−1. Highest N2O emissions per ha were found in countries with a high agricultural intensity, such as the Netherlands, Belgium-Luxembourg, Denmark and Germany. Agricultural soils are a sink for atmospheric methane. An oxidation capacity of 2.5 and 1.5 kg CH4ha−1yr−1was put forward for grasslands and arable land, respectively. Based on land use data of 1993, the CH4sink of agricultural lands in EU-15 was estimated at 303.5 Gg CH4. In general, it could be concluded that N2O emissions from soils (327 Tg CO2equivalents) are far more important than its sink function for CH4(6.3 Tg CO2equivalents).

Abstract:  This paper aims at a better understanding of methane oxidation under conditions that are representative of landfill cover soils. The kinetics of methane oxidation were studied in landfill cover soils that had been exposed to high methane mixing ratios. This was done in batch experiments, under various environmental conditions. V max increased exponentially with temperature in the range 5–35  C, with a Q 10 value of 2.8. K m increased approximately linearly in this range from 1.2 μM to 7 μM. Consequently, the influence of temperature on methane consumption was more pronounced at high concentrations than at low concentrations. The inhibition by ammonium of methane consumption was much stronger after 6–7 months of exposure to high methane mixing ratios than after 5–7 weeks of exposure, indicating that there was a shift of dominating methanotrophic species in soils after long exposure times. Additions of nitrifying sludge or compost to soils initially inhibited methane oxidation, followed by a stimulation after a few days.

Abstract:  A neutral and an acidic soil were treated with different doses (0–3,000 mg Cu kg–1 soil as CuSO4) of copper. The percentages of inhibition of nitrification in both soils varied from 5 to 97%, but for the N mineralization these percentages varied from 8 to 65%. The toxic effect of Cu for basal nitrification and N mineralization was assessed as critical. Nitrification was more sensitive than ammonification to copper toxicity. It appears that an ecological dose of inhibition for nitrification and N mineralization higher than 10% is suitable as an indicator for Cu contamination. Soil resiliency assessed by N mineralization in the lime treatments varied from 11 to 154% in the sandy soil and from 70 to 168% in the sandy loam soil. A combined application of lime and compost significantly increased soil resiliency. The percentage increase varied from 904 to 1,390% in the sandy soil and from 767 to 2,230% in the sandy loam soil. It appears that compost was a powerful agent for recovering the soil fertility of Cu-contaminated soils as assessed by N transformation. The acidic sandy soil showed a lower capacity for recovery after Cu toxicity stress.

Abstract:  The emission of N2O from soybean plants treated with the herbicides dichlorophenoxyacetic acid (2,4-D) and bromoxynil was studied. The N2O flux from 2,4-D- and bromoxynil-treated soybean was 14.1 ng N2O-N g–1 fresh weight h–1 and 19.7 ng N2O-N g–1 fresh weight h–1, respectively, i.e. approximately twice that of the controls. The NO2–-N concentration in 2,4-D- and in bromoxynil-treated soybean was about 8 μg N g–1 fresh weight, i.e. fivefold the concentration found in control plants. The NO3– content in herbicide-treated soybean did not differ significantly from that of the control plants. Consequently, the accumulation of NO2–-N during the assimilation of NO3–-N was thought to cause the observed N2O release. Probably, N2O is a by-product produced during either the reaction of NO2–-N with plant metabolites or NO2–-N decomposition. Final conclusions must await further experiments.

Photoacoustic detection of gases in the air phase in combination with a multipoint sampling device transfers about 100 mL of air from each sample location to the next one, causing a considerable disturbance when small systems are sampled. In reactive systems, such as trace gas exchange in soil samples, a correction is required to determine the kinetic behavior of the systems. But this kinetic behavior is required in turn to calculate the correction in a repeated sampling sequence. A model was developed for reaction kinetics (zero-order or first-order) within closed systems and the sample transfer between these systems by a CBISS MK2 multipoint sampling system, connected with a Brüel & Kjaer photoacoustic detector. By regression, the reaction kinetics is determined, and by simulation of the system in the absence of sample transfer, corrected data are generated. Comparison of experimental and modeled data revealed that part of the sample is transferred directly two systems further. In addition, a slight memory effect of the detector was revealed. These effects were accounted for in the model. If the correction is not made, biased results are obtained for the reaction kinetics.

In 1995 a working group was assembled at the request of OECD/IPCC/IEA to revise the methodology for N2O from agriculture for the National Greenhouse Gas Inventories Methodology. The basics of the methodology developed to calculate annual country level nitrous oxide (N2O) emissions from agricultural soils is presented herein. Three sources of N2O are distinguished in the new methodology: (i) direct emissions from agricultural soils, (ii) emissions from animal production, and (iii) N2O emissions indirectly induced by agricultural activities. The methodology is a simple approach which requires only input data that are available from FAO databases. The methodology attempts to relate N2O emissions to the agricultural nitrogen (N) cycle and to systems into which N is transported once it leaves agricultural systems. These estimates are made with the realization that increased utilization of crop nutrients, including N, will be required to meet rapidly growing needs for food and fiber production in our immediate future. Anthropogenic N input into agricultural systems include N from synthetic fertilizer, animal wastes, increased biological N-fixation, cultivation of mineral and organic soils through enhanced organic matter mineralization, and mineralization of crop residue returned to the field. Nitrous oxide may be emitted directly to the atmosphere in agricultural fields, animal confinements or pastoral systems or be transported from agricultural systems into ground and surface waters through surface runoff. Nitrate leaching and runoff and food consumption by humans and introduction into sewage systems transport the N ultimately into surface water (rivers and oceans) where additional N2O is produced. Ammonia and oxides of N (NOx) are also emitted from agricultural systems and may be transported off-site and serve to fertilize other systems which leads to enhanced production of N2O. Eventually, all N that moves through the soil system will be either terminally sequestered in buried sediments or denitrified in aquatic systems. We estimated global N2O–N emissions for the year 1989, using midpoint emission factors from our methodology and the FAO data for 1989. Direct emissions from agricultural soils totaled 2.1 Tg N, direct emissions from animal production totaled 2.1 Tg N and indirect emissions resulting from agricultural N input into the atmosphere and aquatic systems totaled 2.1 Tg N2O–N for an annual total of 6.3 Tg N2O–N. The N2O input to the atmosphere from agricultural production as a whole has apparently been previously underestimated. These new estimates suggest that the missing N2O sources discussed in earlier IPCC reports is likely a biogenic (agricultural) one.

Agricultural practices, soil characteristics and meteorological conditions are responsible for eventual nitrate accumulation in the subsoil. There is a lot of evidence that denitrification occurs in the subsoil and rates up to 60–70 kg ha-1yr-1might be possible. It has also been shown that in the presence of Fe2+(formed through weathering of minerals) and an alkaline pH, nitrate can be chemically reduced. Another possible pathway of disappearance is through the formation of nitrite, which is unstable in acid conditions. With regard to the emission of N2O and N2, it can be stated that all conditions whereby the denitrification process becomes marginal are favourable for N2O formation rather than for N2. Because of its high solubility, however, an important amount of N2O might be transported with drainage water.

Some factors influencing methane emission from a freshwater wetland in Belgium were studied. Seasonal fluctuations of methane emission rates, influence of drainage capacity and depth of methane production on methane emission, as well as in situ methane oxidation were monitored. From March until December, methane fluxes varying between 0 and 102 mg CH4m−2d−1were measured. During this period, a total emission of 60 kg CH4ha−1was calculated. Statistical analysis of these emission data showed that soil moisture was a more important controlling parameter than soil temperature. Depending on the drainage capacity of the selected area, different emission rates were observed. Sites with a “bad natural drainage” and a “fairly bad natural drainage” showed average fluxes of 5.41 and 2.04 mg CH4m−2d−1, respectively, during July. The area with an “insufficient natural drainage” had an emission of 1.44 mg CH4m−2d−1. Using methyl fluoride as a specific inhibitor for methane oxidation, it was found that 34 to 67% of the produced methane could be oxidized. Methane emission was found to decrease with increasing soil depth. With diffusion chambers placed on the soil surface, a CH4release of 40.0 kg CH4ha−1(March–June) was found. With chambers placed at 150‐ and 300‐mm depths, emission rates of 11.3 and 3.3 kg CH4ha−1, respectively, were calculated. Obviously, most of the emitted methane was produced in the upper organic soil layer.

Ammonium (NH+) inhibits the microbial oxidation of methane (CH4), and gives rise to the formation of nitrous oxide (N2O) in aerobic soils. However, the NH+4concentration in the soil water is not necessarily proportional to the total NH+4concentration in the soil, due to cation exchange or fixation phenomena. It was found that introducing the concept of ion exchange or fixation in kinetic models on CH4consumption and N2O formation can increase our knowledge on these processes in soils. A fit of these kinetic models with experimental data showed a standard deviation of slightly more than 10%. The effects of NH+4on CH4oxidation and N2O formation can only be compared in soils with the same cation exchange capacity (CEC).

ABSTRACTCation exchange capacity (CEC) and reducing capacity (RC) in relation to compost stability and quality were studied. The results show that grape prunings, husks and seeds compost and vine branches compost were nearly stabilized after 120 days of composting. The CEC of the vine branches compost (23.1–66.5 cmol kg−1) and the grape prunings, husks and seeds compost (98.3–138.7 cmol kg−1) was high during that period. Their reduction power was low and the quality of these composts was very good. The CEC of sawdust composts was noticeably lower (2.9–14.4 cmol kg−1) after 180 days. After 360 days of composting they were nearly stabilized and the CEC drastically increased (80.9–83.8 cmol kg−1). The reduction power of the sawdust composts was high during one full year and they could be applied to the soil with precautions within this period. Next to the cation exchange capacity the reducing capacity appeared to be a reliable and important criterion for compost quality, especially with respect to the protection of soils from intensive reduction processes. Significant correlations among CEC, RC and CO2production were observed during the first 4 months of composting. However, the results can be applied only under defined conditions.

The effect of irradiation with X-rays and electron beams on the microbiological quality of white pepper, sweet red paprika and nutmeg was examined. Statistical analyses were performed on the data to interpret the results on coliforms, total mesophilic counts and thermophilic spores after irradiation with doses ranging from 0 to 10 kGy at different dose rates, 50 Gy/min for X-rays and 1 or 5 kGy/min for electron beams. It was concluded that for the selected dry spices no major differences between the two irradiation techniques were found. Electron paramagnetic resonance (EPR) was employed to detect the ionizing treatment, using the produced radicals. No significant differences were observed between spectra of samples irradiated with electrons or X-rays.

Well‐managed, aerated cover soils can have a mitigating effect on methane emission from landfills. The influence of moisture content, soil temperature, and N on the methane uptake capacity of a neutral landfill cover soil was examined. A soil moisture content of 15% w/w gave the maximum CH4oxidation rate (2.36 ng CH4h−1g−1soil). When wetter, CH4consumption was slower (e.g., 1.6 ng CH4h−1g−1at 30% w/w) because of a limited gas diffusion. At lower soil moisture, microbial activity was reduced and consequently the oxidation capacity decreased (e.g., 0.84 ng CH4h−1g−1at 5% w/w). Optimum temperature was between 25 and 30°C. The calculated activation energy of the CH4oxidation was 56.5 kJ K−1mol−1. After NH+4addition, a negative linear correlation was found between the methane oxidation rate and the nitrous oxide flux (R2= 0.96, Y1 = 2.7 − 0.44 × Y2). Addition of NO−3had no significant effect on CH4oxidation. The effect of organic residue amendments depended on their C/N ratios. Crop residues with a high C/N ratio (wheat [Triticum sativumL.] and maize [Zea maysL.] straw) stimulated N‐immobilization and did not affect the methane‐oxidizing capacity. On the other hand, addition of crop residues with low C/N ratios (potato [Solanum tuberosumL.] and sugar beet [Beta vulgariscv. Altissima] leaves) stimulated N‐mineralization, resulting in a strong inhibition of the methane oxidation.

Summary: To quantify the C-metabolism in micropropagated roses, two labeled substrates were tested:14C-sucrose and14CO2. In the14C-sucrose experiment four parameters were followed during the culture period: the decrease of the radioactivity of the culture medium (by liquid scintillation counting), the dry matter accumulation, the radioactivity of the dry matter, and the radioactivity of the captured CO2. These values were related to the total sucrose uptake, the total biomass increase, the biomass increase by sucrose incorporation, and the sucrose respired as CO2. C-incorporation during photosynthesis was calculated as the difference between total biomass increase and biomass increase by sucrose incorporation. The14CO2 experiment did not allow measurement of the net CO2 fixation in a direct way because the ratio of14CO2 over total CO2 in the headspace of the container could not be kept constant over the culture period. Respiration caused a build up of the CO2 concentration in the headspace. Indirect calculation established a comparable photosynthetic portion of CO2 uptake for the tested variety.