H.A.C. Denier van der Gon

Influence of organic matter incorporation on the methane emission from a wetland rice field.

Methane (CH4) emission from Philippine rice paddies was monitored with a closed chamber technique during the 1992 dry and wet season. CH4 emissions were significantly higher in the dry season. Application of green manure stimulated CH4 emissions. In plots that received more than 11 t ha−1 of fresh green manure, CH4 emission was highest during the first half of the growing season. Significant amounts of CH4 may evolve during or immediately after transplanting, if the organic amendments are incorporated 1 to 3 weeks before transplanting. Laboratory incubations of soil cores show that CH4 production is highest near the soil surface. CH4 production in green manure treated fields is higher than in urea-fertilized fields, but toward the end of the season this difference is less pronounced. Around panicle initiation, the fraction of CH4 produced, which was emitted to the atmosphere, is lower than at tillering or ripening. The impact of organic amendments on CH4 emissions at different locations of the world can be described by a dose response curve, if CH4 emission from organically amended plots is expressed relative to CH4 emission from mineral fertilized plots of the same location and season. Various organic amendments (e.g., straw, fermented residues) have a similar effect on CH4 emissions after correction for differences in easily decomposable carbon content.

Impact of gypsum application on the methane emission from a wetland rice field

Methane emission from Philippine rice paddies was monitored with a closed chamber technique during the 1991 and 1992 wet season. The methane emission from plots amended with 6.66 tons.ha−1 gypsum was reduced by 55–70% compared to non-amended plots. Although CH4 emission from fields with a high input of fresh organic matter was strongly enhanced, the experiments showed that the relative reduction in CH4 emission upon gypsum application was independent of organic matter addition. The reduced CH4 emission upon gypsum application was most likely due to inhibition of methanogenesis by sulfate-reducing bacteria. Observed SO42− concentrations in the soil solution of gypsum-amended plots were well above minimum concentrations reported in the literature for successful competition of sulfate-reducing bacteria with methanogens. The data provide a base for reducing the estimates of CH4 emissions from rice grown on high-sulfate containing soils or gypsum-amended soils.

Release of entrapped methane from wetland rice fields upon soil drying

Methane emissions from Philippine rice paddies, fertilized with either urea or green manure, were monitored for several weeks after harvesting the dry and the wet season crops of 1992. The fields were still flooded during harvest but irrigation was stopped after harvest and the fields were allowed to evaporatively dry while CH4 emissions were monitored with a closed chamber technique. In all plots we observed a sudden, strong increase of CH4 emissions to the atmosphere for 2 to 4 days just after the soil fell dry. As soil drying continued, the soils began to crack and CH4 emissions decreased to nil. The release of CH4 during soil drying was observed for fields on three different soil types and both for urea or organically manured rice fields in both seasons. The absolute amounts of CH4 emitted during soil drying differed greatly depending on fertilizer treatment. However, the ratio between the amount of CH4 released upon soil drying and CH4 emitted during the growing season was quite constant (0.10 ±0.04). This suggests that about 10% of the CH4 emitted during a full rice crop cycle is released during drying of the fields and thus needs to be included in estimates of the total CH4 emission from rice agriculture.

Prediction of reducible soil iron content from iron extraction data.

Soils contain various iron compounds that differ in solubility, reducibility and extractability. Moreover, the contribution of the various iron compounds to total iron (Fe) and total Fe concentrations differs highly among soils. As a result, the total reducible Fe content can also differ among soils, and so does the dynamics of iron reduction. These factors complicate the prediction of reducible Fe based on Fe extraction data and hamper the application of process-based models for reduced or waterlogged soils where redox processes play a key-role. This paper presents a theoretical analysis relating reducible to extractable Fe reported in the literature. Predictions made from this theoretical analysis were evaluated in soil incubations using 18 rice paddy soils from all over the world. The incubation studies and the literature study both show that reducible Fe can be related to Fe from some selected, but not all, iron extractions. The combination of measurements for labile Fe(III)oxides (derived from oxalate-extractable Fe) and stabile Fe(III)oxides (derived from dithionite-citrate-extractable Fe) shows highly significant correlations with reducible Fe with high coefficients of determination (r2 = 0.92−0.95 depending on the definition of stabile Fe(III)oxides). Given the high diversity in rice soils used for the incubations, these regression equations will have general applicability. Application of these regression equations in combination with soil database information may improve the predictive ability of process-based models where soil redox processes are important, such as CH4 emission models derived for rice paddies or wetlands.Soils contain various iron compounds that differ in solubility, reducibility and extractability. Moreover, the contribution of the various iron compounds to total iron (Fe) and total Fe concentrations differs highly among soils. As a result, the total reducible Fe content can also differ among soils, and so does the dynamics of iron reduction. These factors complicate the prediction of reducible Fe based on Fe extraction data and hamper the application of process-based models for reduced or waterlogged soils where redox processes play a key-role. This paper presents a theoretical analysis relating reducible to extractable Fe reported in the literature. Predictions made from this theoretical analysis were evaluated in soil incubations using 18 rice paddy soils from all over the world. The incubation studies and the literature study both show that reducible Fe can be related to Fe from some selected, but not all, iron extractions. The combination of measurements for labile Fe(III)oxides (derived from oxalate-extractable Fe) and stabile Fe(III)oxides (derived from dithionite-citrate-extractable Fe) shows highly significant correlations with reducible Fe with high coefficients of determination (r2 = 0.92−0.95 depending on the definition of stabile Fe(III)oxides). Given the high diversity in rice soils used for the incubations, these regression equations will have general applicability. Application of these regression equations in combination with soil database information may improve the predictive ability of process-based models where soil redox processes are important, such as CH4 emission models derived for rice paddies or wetlands.

Methane emission from a wetland rice field as affected by salinity

The impact of salinity on CH4 emission was studied by adding salt to a Philippine rice paddy, increasing pore water EC to approx. 4 dS.m-1 Methane emission from the salt-amended plot and adjacent control plots was monitored with a closed chamber technique. The addition of salt to the rice field caused a reduction by 25% in CH4 emission. Rates of methane emissions from intact soil cores were measured during aerobic and anaerobic incubations. The anaerobic CH4 fluxes from the salt-amended soil cores were three to four times lower than from cores of the control plot, whereas the aerobic CH4 fluxes were about equal. Measurements of the potential CH4 production with depth showed that the CH4 production in the salt-amended field was strongly reduced compared to the control field. Calculation of the percentage CH4 oxidized of the anaerobic flux indicated that CH4 oxidation in the salt-amended plot was even more inhibited than CH4 production. The net result was about equal aerobic CH4 fluxes from both salt-amended plots and non-amended plots. The data illustrate the importance of both CH4 production and CH4 oxidation when estimating CH4 emission and show that the ratio between CH4 production and CH4 oxidation may depend on environmental conditions. The reduction in CH4 emission from rice paddies upon amendment with salt low in sulfate is considerably smaller than the reduction in CH4 emission observed in a similar study where fields were amended with high-sulfate containing salt (gypsum). The results indicate that CH4 emissions from wetland rice fields on saline, low-sulfate soils are lower than CH4 emissions from otherwise comparable non-saline rice tields. However, the reduction in CH4 emission is not proportional to the reduction in CH4 production

Upscaling regional emissions of greenhouse gases from rice cultivation: methods and sources of uncertainty.

One of the important sources of greenhouse gases is the emission of methane from rice fields. Methane emission from rice fields is the result of a complex array of soil processes involving plant-microbe interactions. The cumulative effects of these processes at the level of individual plants influence the global atmospheric composition and make it necessary to expand our research focus from small plots to large landscapes and regions. However, present extrapolations (‘upscaling’) are tenuous at best because of methodological and practical problems. The different steps taken to calculate regional emission strengths are discussed and illustrated by calculations for a case-study in the Philippines. The applicability of high quality, process-based, models of methane emission at the level of individual plants is limited for regional analysis by their large data requirements. Simplified models can be used at the regional level but are not able to capture the complex emission situation. Data availability and model accuracy are therefore often difficult to match. Other common sources of uncertainty are the quality of input data. A critical evaluation of input data should be made in every upscaling study to assess the suitability for calculating regional emissions. For the case-study we show effects of differences in input data caused by data source and interpolation technique. The results from the case-study and similar studies in literature indicate that upscaling techniques are still troublesome and a cause of large uncertainties in regional estimates. The results suggest that some of the stumbling blocks in the conventional upscaling procedure are almost impassable in the near future. Based on these results, a plea is made for meso-level measurements to calibrate and validate upscaling methods in order to be better able to quantify and reduce uncertainties in regional emission estimates.

Effects of interpolation and data resolution on methane emission estimates from rice paddies

Rice paddies are an important source of the greenhouse gas methane (CH4). Global methane emission estimates are highly uncertain and do not account for effects of interpolation or data resolution errors. This paper determines such scaling effects for the influence of soil properties on calculated CH4 emissions for the island of Java, Indonesia. The effects of different interpolation techniques, variograms and neighbor optimization were tested for soil properties by cross-validation. Interpolated organic carbon values were not significantly different from the original soil samples, in contrast to interpolated soil iron contents. Interpolation of soil properties coupled to a process-based model on CH4emissions led to a significant change in distribution of calculated CH4 emissions, i.e., the variance decreased. Effects of data resolution were examined by interpolating soil properties to derive data at different data resolutions and then calculating CH4 emissions by applying the process-based model at these resolutions. The soil properties did not differ significantly for different data resolutions, in contrast to calculated CH4 emissions. These scaling effects were caused by the combination of interpolation and a non-linear model. Real scaling effects may even be larger because small-scale variability was not accounted for. Scaling effects, including those caused by small-scale variability, have to be considered to achieve unbiased and less uncertain global CH4emissions estimates from rice paddies.

Soil parameters controlling methane emission from rice paddies.

Abstract The influence of soil parameters on methane emissions from rice paddies is studied in a collaborative project of Agricultural University Wageningen and the International Rice Research Institute (IRRI). Methane fluxes from wetland rice fields in the Philippines were monitored with a closed chamber technique during two wet seasons (1991 and 1992) and one dry season (1992). Gypsum addition and salinity were found to reduce CH 4 emissions whereas green manuring strongly enhanced the CH 4 fluxes from rice fields. Laboratory experiments with planted pots showed that plant-mediated CH 4 transport is diffusion controlled and that rhizospheric CH 4 oxidation may depend on the plant growth stage.

Assessment report on NRP subtheme “gGeenhouse Gases”: Sources and sinks of CO2CH4 and N2O, databases and socio-economic causes

Abstract The aim of the subtheme Greenhouse gases of the Dutch National Research programme on (NRP) is to quantify the sources and sinks of the major greenhouse gases to enable estimates of the future atmospheric concentration. The major part of the projects in this theme is focused on the Dutch situation, but the results can be extrapolated countries or regions. The information gained will be used for Dutch policy decisions regarding abatement of greenhouse gases. Section 1 deals with the aim and organization of Causes of climate change, and relates the scope to increased awareness of uncertainties in sources and sinks of greenhouse gases: at the start of the National Research Programme the general consensus of the scientific community was that these uncertainties were not extreme large, it is nowadays accepted that these uncertainties are larger than assumed before. The aim the Cluster CO 2 ( Section 2 ) was devoted to study the exchange between terrestrial ecosystems and the atmosphere to gain more knowledge of the “fertilization” flux. The research was mainly focused on the development of a CO 2 exchange model for grassland describing diurnal and seasonal fluxes, and on the validation of this local scale model on a regional and national scale. In both the clusters CH 4 and N 2 O (respectively Section 3 and Section 4 ) anthropogenic and biogenic sources were studied. Major criteria to study sources were the source strength, but also the uncertainty in the source estimate and the potential emission reduction, all projected on the Dutch situation. Exception were the projects on CH 4 emission from rice fields, and the sea/air exchange of N 2 O in oceans; expertise was available in The Netherlands to carry out these studies. As in the sub-theme CO 2 the study of processes in grasslands was given a high priority in the sub themes CH 4 and N 2 O in order to quantify emission the mentioned greenhouse gases. Moreover, in the CH 4 -sub theme projects were performed to evaluate and validate the strength of various sources. The two remaining clusters (limited in extend) were aimed at the development of emission databases and geographic quantification of soil processes controlling greenhouse gas fluxes (cluster Database Development, Section 5 ), and on national inventories (cluster Socio-economic Causes, Section 6 ). In the framework of the first cluster two databases were developed, one was the World Inventory of Soil Emission potentials (WISE), a global gridded database of the primary soil factors controlling soil greenhouse gas emissions, and the other was Emission Database for Global Atmospheric Research (EDGAR) aimed to describe the processes as land use, energy consumption etc, which control the emissions of greenhouse gases and other air pollutants. The goal of the other sub theme was to develop and apply methodologies to compile national inventories of greenhouse gas emissions in The Netherlands, focused on the compounds CH 4 and N 2 O.