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The effect of tillage on the overall greenhouse gas balance of croplands is not clear. It has been suggested that ceasing tillage increases C sequestration, but has the risk of enhancing NO emission, which could switch the greenhouse gas balance from negative to positive. We studied the short-term effect of tillage intensity on NO and CO emissions. We changed reduced tillage to conventional tillage or no tillage and performed two tillage operations in two growing seasons. All other parameters such as agricultural management, climate, and crop type at the study site, an intermediately aerated Luvisol in Belgium, were similar. Nitrous oxide and CO emissions were measured event-directed about 40 times per year from September 2006 until December 2008 using a closed chamber technique. We did not observe any significant short-term effect of tillage intensity on NO emissions during the 2 years following tillage conversion. The 2-year aggregated NO emission was not affected by the absence of tillage, 5.6 kg NO-N ha, compared to conventional tillage, 4.6 ± 0.9 kg NO-N ha, or reduced tillage, 4.7 ± 0.3 kg NO-N ha. Enhanced NO emission events in the absence of tillage, 1 year after conversion, could be explained by the combination of higher N application and wetter conditions. Conversion to conventional tillage caused a small, but significant, increase in CO emission over the same period. We conclude that in the short term, none of the tillage intensities had an effect on NO emission, and the effect on CO emission was slightly positive when tillage intensity increased. A low short-term risk of increased NO emission in the absence of tillage in well-aerated croplands is beneficial agro-environmentally, but the long-term effect should also be assessed via follow-up studies. [ABSTRACT FROM AUTHOR]

Approximately 60% of Mexico (1.973 × 106 km2) is arid or semi-arid with vegetation dominated by N2 fixing shrubs, such as mesquite (Prosopis juliflora). Little is known, however, how these ecosystems contribute to production of nitrous oxide (N2O), a known greenhouse gas. We investigated this by adding inorganic fertilizer (20 mg ammonium (NH4+) N kg-1 soil) to soil at different water contents (40%, 60%, 80%, and 100% of water-holding capacity (WHC)) sampled under the canopy of mesquite and outside its canopy, while production of carbon dioxide (CO2) and nitrous oxide (N2O), and dynamics NH4+, nitrite (NO2-), and nitrate (NO3-)) were monitored. The CO2 production rate was 1.5 times larger for soil sampled under the canopy of mesquite compared to soil sampled outside the canopy of shrubs and lower in soil incubated at 100% WHC compared to the other treatments. Production of N2O increased with increased water content within the first day, but decreased in soil at 80% and 100% WHC thereafter. The production of N2O was 1.9 times larger for soil sampled under the canopy of mesquite compared to soil sampled outside its canopy. The addition of 20 mg NH4+-N increased production of N2O 1.8-fold. It was found that the cumulative production of N2O was larger from soil sampled under the canopy of mesquite than outside it when amended with inorganic fertilizer and increased with increased water content of the soil within a day. The relationship between the emission of CO2 and N2O, water-holding capacity are discussed. [ABSTRACT FROM AUTHOR]

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. botrytis L.) residues (~73 Mg fresh matter ha 1) together with an immobilizer waste (~5 Mg C ha-1 of 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-1 of 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 N3- 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 N3- 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 N3- leaching; however, stimulating remineralization of immobilized N by the start of the following spring may not be easy to achieve. [ABSTRACT FROM AUTHOR]

Old-growth forests of southern Chile represent an important reserve of temperate (rain) forests in the world. Wetter and colder forest ecosystems appear to be more efficient in conserving and recycling N such that mostly non-plant available N species are lost, which could be indicated by more depleted δ 15 N values of the soil and plants. Hydrological N loss from the old-growth forests in southern Chile occurs mainly via dissolved organic nitrogen and not via dissolved inorganic N. Forest disturbances ( e.g . fire, clear-cutting or enhanced N deposition) cause (abrupt) changes in ecosystem N-cycling processes. In this study, we hypothesized that δ 15 N signatures of soil profiles under old-growth forests could be used as an integrator for ecosystem N-cycling, and changes of these δ 15 N profiles could be valuable to assess ecosystem resilience towards disturbances. Six old-growth forests were selected in the phytogeographical region of the Valdivian rain forest in southern Chile. One of the sites has been partly burned in February 2002. First, we observed that ecosystems with higher mean annual precipitation and lower mean annual temperature were relatively more depleted in 15 N. Secondly, we found that a forest fire caused a 100-fold increase of the nitrate export and induced an enrichment of the soil δ 15 N signal in the upper 20 cm. [ABSTRACT FROM AUTHOR]

Since the early 1990s, we have been carrying out experiments on N2O production, emission and sorption from a variety of soils and ecosystems. These laboratory studies revealed insights on the complex process of N2O formation in soils under contrasting conditions. Within Belgium, we also carried out numerous field experiments to measure in situ N2O emissions, using the closed chamber technique. The latter allowed us to suggest a region-specific N2O-N emission factor (2.66% of the applied N) for direct soil emissions and to assess the spatial and temporal variability of N2O emissions. Recently, we have been using these N2O field emission data to validate an adapted version of the DNDC process-based model to predict direct N2O emissions from agricultural soils of the Flemish region. Ultimately, it is our aim to develop, based on this validated DNDC model, scenario analyses of future direct N2O emissions from agricultural soils. [ABSTRACT FROM AUTHOR]

Abstract Evaluations of soil organic carbon (SOC) stocks are often based on assigning a carbon density to each one of a number of ecosystems or soil classes considered, using data from soil profiles within these categories. A better approach, in which the use of classification methods by which extrapolation of SOC data to larger areas is avoided, can only be used if enough data are available at a sufficiently small scale. Over 190 000 SOC measurements (0–24 cm) have been made in the Flemish cropland (the Northern part of Belgium) in the 1989–2000 period. These SOC data were grouped into 3-year periods and as means plus standard deviation per (part of) community (polygons). This large dataset was used to calculate SOC stocks and their evolution with time, without data extrapolation. Using a detailed soil map, larger spatial groups of polygons were created based on soil texture and spatial location. Linear regression analysis showed that in the entire study area, SOC stocks had decreased or at best had remained stable. In total, a yearly decrease of 354 kton OC yr-1 was calculated, which corresponds with a net CO2 emission of 1238 kton CO2 yr-1 . Specific regions with a high carbon sequestration potential were identified, based on SOC losses during the 1989–2000 period and the mean 1999 SOC content, compared to the average SOC content of soils in Flanders with a similar soil texture. When restoring the SOC stocks to their 1990 level, we estimated the carbon sequestration potential of the Flemish cropland soils to be some 300 kton CO2 yr-1 at best, which corresponds to a 40-year restoration period. In conclusion, we can say that in regions where agricultural production is very intense, carbon sequestration in the cropland may make only a very modest contribution to a country's effort to reduce greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Strategies used to reduce emissions of N2O and CH4 in 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 CH4 emission 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 CH4 was 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 CH4 was 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 CH4 emission 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 CH4 emission. 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. [ABSTRACT FROM AUTHOR]

Net N mineralization was studied in three different forest sites (Belgium): a mixed deciduous forest with oak ( Quercus robur L . and Quercus rubra L .) and birch ( Betula pendula Roth) as dominant species, a deciduous stand of silver birch ( Betula pendula) and a coniferous stand of Corsican pine ( Pinus nigra ssp . Laricio). The organic (F + H) layer and mineral soil at different depths (0–10, 10–20 and 20–30 cm) were sampled at three locations in the mixed deciduous forest (GE, GF1, GF2), at one location in the silver birch stand (SB) and one in the Corsican pine stand (CP). All samples were incubated over 10 weeks under controlled temperature and moisture conditions. The net N mineralization rates in the organic and upper mineral layer (0–10 cm) were found to be significantly different from the other layers and accounted for 66–95% of the total mineralization over the first 30 cm. Net N mineralization rates in the organic layer ranged from 4.2 to 27.3 mg N m–2 day–1. Net N mineralization and nitrification rates were positively correlated. For the mineral soil, net N mineralization rates decreased with depth and the upper 10 cm showed significantly higher rates, ranging from 8.9 to 33.5 mg N m–2 day–1. The rates of the 10–20 cm and 20–30 cm sublayers were similar, ranging from 1.2 to 7.4 mg N m–2 day–1. The net N mineralization rates for the total mineral layer (0–30 cm) ranged from 17.4 mg N m–2 day–1 (SB) to 36.1 mg N m–2 day–1 (CP). Both from PCA and multiple regression analysis, we could conclude that net N mineralization rates were closely related to the initial mineral N content (Ninitial). Furthermore, significant correlations were observed between the net N mineralization rate, the total carbon (TC) and NH4 +-N content for the mineral layers and between net N mineralization rate, total nitrogen (TN), hemicellulose content and C/N for the organic layers. [ABSTRACT FROM AUTHOR]

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. Vmax increased exponentially with temperature in the range 5–35 °C, with a Q10 value of 2.8. Km 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 FROM AUTHOR]

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 FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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-1 yr-1 might 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. [ABSTRACT FROM AUTHOR]

Presents a study conducted on factors influencing methane emmission from a freshwater wetland in Belgium. Monitoring of drainage capacity and depth of methane production influence on methane emmision; Statistical analysis of emmision data from March to December, 1997; What sites with bad natural drainage and fairly bad natural drainage showed; Description of field experiment; Results of the study.

Studies carbon mineralization and nitrogen transformation during decomposition of sunflower stalks and wheat straw with and without addition of ammonium sulphate in a Vertisol. Use of isotopic dilution technique to calculate nitrogen immobilization; Role of high inorganic nitrogen content of stalks in suppressing the nitrogen immobilization; Carbon-nitrogen relationship during the decomposition of divers carbon substrates.