Methane and nitrous oxide emissions from irrigated lowland rice paddies after wheat straw application and midseason aeration

Straw application and midseason drainage play role in controlling methane (CH₄) and nitrous oxide (N₂O) emissions from rice paddy fields, but little information is available on their integrative effect on CH₄ and N₂O emissions. A two-year field experiment was conducted to study the combined effect of timing and duration of midseason aeration and wheat straw incorporation on mitigation of global warming potential (GWP) of CH₄ and N₂O emissions from irrigated lowland rice paddy fields. Results showed that incorporation of wheat straw increased CH₄ by a factor of 5–9 under various water regimes, but simultaneously decreased N₂O emission by 19–42 % during the rice growing season. Without straw incorporation, prolonged aeration significantly reduced the net 100-year GWP of CH₄ and N₂O emissions by 6 %, but also decreased rice production when compared with normal aeration. With straw incorporation, the lowest GWP was found by early aeration, which reduced GWP by 7 and 20 % in 2007 and 2008, respectively. Estimation of net GWPs of CH₄ and N₂O emissions indicated that early midseason drainage with straw incorporation offered the potential to mitigate CH₄ and N₂O emissions from irrigated lowland rice paddies in China.     

Integrated management practices significantly affect N2O emissions and wheat–maize production at field scale in the North China Plain

In the North China Plain, a field experiment was conducted to measure nitrous oxide (N₂O) and methane (CH₄) fluxes from a typical winter wheat–summer maize rotation system under five integrated agricultural management practices: conventional regime [excessive nitrogen (N) fertilization, flood irrigation, and rotary tillage before wheat sowing; CON], recommended regime 1 (balanced N fertilization, decreased irrigation, and deep plowing before wheat sowing; REC-1), recommended regime 2 (balanced N fertilization, decreased irrigation, and no tillage; REC-2), recommended regime 3 (controlled release N fertilizer, decreased irrigation, and no tillage; REC-3), and no N fertilizer (CK). Field measurements indicated that pulse emissions after N fertilization and irrigation contributed 19–49 % of annual N₂O emissions. In contrast to CON (2.21 kg N₂O-N ha^?1 year^?1), the other treatments resulted in significant declines in cumulative N₂O emissions, which ranged from 0.96 to 1.76 kg N₂O-N ha^?1 year^?1, indicating that the recommended practices (e.g., balanced N fertilization, controlled release N fertilizer, and decreased irrigation) offered substantial benefits for both sustaining grain yield and reducing N₂O emissions. Emission factors of N fertilizer were 0.21, 0.22, 0.23, and 0.37 % under CON, REC-1, REC-3, and REC-2, respectively. Emissions of N₂O during the freeze–thaw cycle period and the winter freezing period accounted for 9.7 and 5.1 % of the annual N₂O budget, respectively. Thus, we recommend that the monitoring frequency should be increased during the freeze–thaw cycle period to obtain a proper estimate of total emissions. Annual CH₄ fluxes from the soil were low (?1.54 to ?1.12 kg CH₄-C ha^?1 year^?1), and N fertilizer application had no obvious effects on CH₄ uptake. Values of global warming potential were predominantly determined by N₂O emissions, which were 411 kg CO₂-eq ha^?1 year^?1 in the CK and 694–982 kg CO₂-eq ha^?1 year^?1 in the N fertilization regimes. When comprehensively considering grain yield, global warming potential intensity values in REC-1, REC-2, and REC-3 were significantly lower than in CON. Meanwhile, grain yield increased slightly under REC-1 and REC-3 compared to CON. Generally, REC-1 and REC-3 are recommended as promising management regimes to attain the dual objectives of sustaining grain yield and reducing greenhouse gas emissions in the North China Plain.     

Emissions of CH4, N2O, NH3 and odorants from pig slurry during winter and summer storage

Manure storage contributes significantly to greenhouse gas (GHG), NH₃ and odour emissions from intensive livestock production. A pilot-scale facility with eight 6.5-m³ slurry storage units was used to quantify emissions of CH₄, N₂O, NH₃, and odorants from pig slurry during winter and summer storage. Pig slurry was stored with or without a straw crust, and with or without interception of precipitation, i.e., four treatments, in two randomized blocks. Emissions of total reduced S (mainly H₂S) and p-cresol, but not skatole, were reduced by the straw crust. Total GHG emissions were 0.01–0.02 kg CO₂ eq m^?3 day^?1 during a 45-day winter storage, and 1.1–1.3 kg CO₂ eq m^?3 day^?1 during a 58-day summer storage period independent of storage conditions; the GHG balance was dominated by CH₄ emissions. Nitrous oxide emissions occurred only during summer storage where, apparently, emissions were related to the water balance of the surface crust. An N₂O emission factor for slurry storage with a straw crust was estimated at 0.002–0.004. There was no evidence for a reduction of CH₄ emissions with a crust. Current Intergovernmental Panel on Climate Change recommendations for N₂O and CH₄ emission factors are discussed.     

Methane and Nitrous Oxide Emissions from Rice Field and Related Microorganism in Black Soil, Northeastern China

Methane (CH₄) and nitrous oxide (N₂O) emissions from rice field in black soil were measured in situ by using static chamber techniques during crop growth season in 2001. The experiment fields were divided into three plots for three different treatments, one with continuous flooded and applying urea (CU), one with continuous flooded and applying slow-releasing urea (CS), and one with intermittent irrigation and applying urea (IU). Under the same fertilization application, compared with continuous flooded, intermittent irrigation can significantly reduce CH₄ emission and increase N₂O emission. But, integrated global warming potentials (GWP_S) of CH₄ and N₂O emission were reduced greatly, while rice yield was not affected. So, the intermittent irrigation is an effective measure to reduce greenhouse gas emissions from paddy fields. The amount of CH₄ emission during rice-growing season for the three treatments was all much lower than that from any other region in China. There was a trade-off relationship between CH₄ and N₂O emissions. We also measured the numbers of methanogens, methanotrophs, nitrifiers and denitrifers from rice field at various growth stages in 2001. Bacteria populations were estimated by the most probable number (MPN) method. Regression analyses show CH₄ emissions were closely related to methanogens population for all the three treatments. There was a positive correlation between denitrifiers population level and N₂O emission in the treatment of IU.     

A category for estimate of CH4 emission from rice paddy fields in China

Based on key factors influencing CH₄ fluxes from rice paddy fields in China, a category for estimation of total CH₄ emission was suggested and the constraints for the estimation were discussed in the paper. Recently, CH₄ fluxes measured in situ have been built up dramatically with the efforts of both Chinese scientists and those from abroad. After reviewing published data on CH₄ fluxes from rice paddy fields, we found that although there are many other influencing factors, water regime and organic manure application are two key factors controlling CH₄ emission; thus, rice paddy fields in China were classified by these two factors to estimate CH₄ emission. In the suggested category, the water regime of rice paddy fields was classified into mid-season aeration at least once during the period of rice growth (MSA), continuous flooding during the period of rice growth but well-drained after rice harvest (CFD), and permanent flooding (PF) even in winter, and fertilization was classified into mineral fertilizers only (MIN), amendment with organic manures at the rate of less than or equal to 15 t ha^-1 (MU < 15) and at the rate of higher than 15 t ha^-1 (MU > 15), and with rice straw or other fresh plant materials (RS). Combining both water regime and fertilization together, we classified rice paddy fields in China into 12 types. The seasonal mean CH₄ flux of each type of rice paddy field was calculated by the data available and showed that the lowest CH₄ flux was found in the type MSA-MIN, and the highest in PF-MU > 15. The total emission estimated by this category was 8.05 Tg CH₄ yr^-1 with a standard deviation of 3.69 Tg CH₄ yr^-1. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nitrous oxide and methane emissions from cultivated seasonal wetland (dambo) soils with inorganic,organic and integrated nutrient management

In many smallholder farming areas southern Africa, the cultivation of seasonal wetlands (dambos) represent an important adaptation to climate change. Frequent droughts and poor performance of rain-fed crops in upland fields have resulted in mounting pressure to cultivate dambos where both organic and inorganic amendments are used to sustain crop yields. Dambo cultivation potentially increases greenhouse gas (GHG) emissions. The objective of the study was to quantify the effects of applying different rates of inorganic nitrogen (N) fertilisers (60, 120, 240 kg N ha^?1) as NH₄NO₃, organic manures (5,000, 10,000 and 15,000 kg ha^?1) and a combination of both sources (integrated management) on GHG emissions in cultivated dambos planted to rape (Brassica napus). Nitrous oxide (N₂O) emissions in plots with organic manures ranged from 218 to 894 µg m^?2 h^?1, while for inorganic N and integrated nutrient management, emissions ranged from 555 to 5,186 µg m^?2 h^?1 and 356–2,702 µg m^?2 h^?1 respectively. Cropped and fertilised dambos were weak sources of methane (CH₄), with emissions ranging from ?0.02 to 0.9 mg m^?2 h^?1, while manures and integrated management increased carbon dioxide (CO₂) emissions. However, crop yields were better under integrated nutrient management. The use of inorganic fertilisers resulted in higher N₂O emission per kg yield obtained (6–14 g N₂O kg^?1 yield), compared to 0.7–4.5 g N₂O kg^?1 yield and 1.6–4.6 g N₂O kg^?1 yield for organic manures and integrated nutrient management respectively. This suggests that the use of organic and integrated nutrient management has the potential to increase yield and reduce yield scaled N₂O emissions.     

Simultaneous Records of Methane and Nitrous Oxide Emissions in Rice-Based Cropping Systems under Rainfed Conditions

Rainfed rice (Oryza sativa L.)-based cropping systems are characterized by alternate wetting and drying cycles as monsoonal rains come and go. The potential for accumulation and denitrification of NO₃ ^– is high in these systems as is the production and emission of CH₄ during the monsoon rice season. Simultaneous measurements of CH₄ and N₂O emissions using automated closed chamber methods have been reported in irrigated rice fields but not in rainfed rice systems. In this field study at the International Rice Research Institute, Philippines, simultaneous and continuous measurements of CH₄ and N₂O were made from the 1994 wet season to the 1996 dry season. During the rice-growing seasons, CH₄ fluxes were observed, with the highest emissions being in organic residue-amended plots. Nitrous oxide fluxes, on the other hand, were generally nonexistent, except after fertilization events where low N₂O fluxes were observed. Slow-release N fertilizer further reduced the already low N₂O emissions compared with prilled urea in the first rice season. During the dry seasons, when the field was planted to the upland crops cowpea [Vigna unguiculata (L.) Walp] and wheat (Triticum aestivum L.), positive CH₄ fluxes were low and insignificant except after the imposition of a permanent flood where high CH₄ fluxes appeared. Evidences of CH₄ uptake were apparent in the first dry season, especially in cowpea plots, indicating that rainfed lowland rice soils can act as sink for CH₄ during the upland crop cycle. Large N₂O fluxes were observed shortly after rainfall events due to denitrification of accumulated NO₃ ^–. Cumulative CH₄ and N₂O fluxes observed during this study in rainfed conditions were lower compared with previous studies on irrigated rice fields.     

Influences of free-air CO2 enrichment (FACE), nitrogen fertilizer and crop residue incorporation on CH4 emissions from irrigated rice fields

To investigate the response of methane (CH₄) emissions to an elevated atmospheric carbon dioxide (CO₂) concentration (200?±?40???mol?mol^?1 higher than the ambient atmosphere), we performed a 4-year multi-factorial experiment at a subtropical rice paddy that contained sandy loam soil in the Yangtze River Delta from 2004 to 2007 using free-air CO₂ enrichment (FACE) technology. Our results revealed that the elevated atmospheric CO₂ increased the seasonal cumulative CH₄ emissions by 15?% on average during the 4-year period. The increase was insignificant and much weaker than the previous studies, which might be primarily attributed to the absence of a significant difference in the rice biomass between the two CO₂ levels in half of the field treatments. Crop residue incorporation hindered the stimulatory effects induced by the elevated CO₂, which were 37, 14 and 6?% for the fields that were incorporated with none, half or all of the wheat straws that were harvested in the preceding winter wheat season, respectively. Nitrogen fertilizers application also hindered the stimulatory effects of the elevated CO₂ on the CH₄ emissions. The CO₂ stimulatory effect was 39?% for the field without nitrogen fertilizers, and reduced to 17, 7 and 5?% for the field with nitrogen fertilization of 125, 250 and 350?kg?N?ha^?1, respectively. The regulation of nitrogen fertilizers on the CO₂ effects in this experiment does not well agree with the previous studies, which might because the soil type was different from those of the previous studies. Thus, further studies are necessary to evaluate the role of soil properties in regulating the effects of elevated atmospheric CO₂ on CH₄ emissions from managed and natural wetlands. There were no significant interactions between the atmospheric CO₂ and the incorporations of nitrogen fertilizer and crop residue. Appropriate experiments are necessary for better understanding of the interact influences of the elevated CO₂ and farm managements.     

Environmental and economic opportunities of applications of different types and application methods of chemical fertilizer in rice paddy

Mitigating greenhouse gas (GHG: Methane and nitrous oxide) emission from the rice cropland vis-à-vis increasing rice yield is one of the important challenges to the food security and climate change research. N-fertilizer input to the crop land is the key to rice productivity and GHG emission from soil. The sustainability of different types and application methods of N-fertilizers in rice cropland was studies based on the net annual C-equivalent GHG emission (CE) and total financial profit to the farmers’. The study was conducted in a low lying experimental rice field of eastern India during two consecutive years. The experiment was laid down with five replicates of the following treatments: (1) control (no N-fertilizer); (2) broadcasting ammonium sulphate (AS); (3) prilled urea (PU) and (4) deep placement of urea briquette (UB). Compared to other treatments, significantly higher GHG emission and grain yield (5–20% higher over other fertilizer applied plots) were recorded from the PU and UB applied plots respectively. Net CE was calculated using the GHG emission and secondary CE of different processes used in each treatment. The net CE followed the order: PU > UB > Control > AS. The ratio of total grain-C to net CE was significantly higher from the AS (15–51%) and UB (8–34%) plots compared to the PU applied plots. Net financial benefit ($ ha^?1) to the farmers’ followed the order: UB > AS > Control > PU. Study indicates that UB may be a climatically sustainable mitigation option in the tropical rice paddy.     

Greenhouse gas emissions from tropical peatlands of Kalimantan,Indonesia

Greenhouse gas emissions were measured from tropical peatlands of Kalimantan, Indonesia. The effect of hydrological zone and land-use on the emission of N₂O, CH₄ and CO₂ were examined. Temporal and annual N₂O, CH₄ and CO₂ were then measured. The results showed that the emissions of these gases were strongly affected by land-use and hydrological zone. The emissions exhibited seasonal changes. Annual emission of N₂O was the highest (nearly 1.4 g N m^–2y^–1) from site A-1 (secondary forest), while there was no signi.cant difference in annual N₂O emission from site A-2 (paddy field) and site A-3 (rice-soybean rotation field). Multiplying the areas of forest and non-forest in Kalimantan with the emission of N₂O from corresponding land-uses, the annual N₂O emissions from peat forest and peat non-forest of Kalimantan were estimated as 0.046 and 0.004 Tg N y^–1, respectively. The emissions of CH₄ from paddy field and non-paddy field were estimated similarly as 0.14 and 0.21 Tg C y^–1, respectively. Total annual CO₂ emission was estimated to be 182 Tg C y^–1. Peatlands of Kalimantan, Indonesia, contributed less than 0.3 of the total global N₂O, CO₂ or CH₄ emission, indicating that the gaseous losses of soil N and C from the study area to the atmosphere were small.     

Methane emissions from a rice agroecosystem in South China: Effects of water regime, straw incorporation and nitrogen fertilizer

To quantitatively assess the effects of agricultural practices on methane (CH₄) emissions from rice fields, a two-year (2005/2006) field experiment with 2³ factorial designs was conducted to assess the effects of three driving factors on CH₄ emissions in South China: continuously flooded (W0) and mid-season and final drainages (W2), straw (S1) and nitrogen fertilizer (N1) applications and their controls (S0, N0). Results showed that averaged across all the treatments about 75?% of the seasonal total CH₄ occurred between the rice transplanting and booting stage, while constituted only 33?% of the seasonal total rice biomass during the same period. Averaged across the treatments in 2006, CH₄ emissions were substantially decreased by mid-season drainage up to 60?% (15.6 vs. 39.0?g?m^?2). The decreased CH₄ emissions represented almost all of the decrease in the total global warming potentials. Without straw incorporation CH₄ emissions substantially decreased up to 59?% (15.9 vs. 38.7?g?m^?2). The stimulating effects of straw were significantly greater for W0 than W2 treatment, being also greater in the 2005 than in the 2006 season. A significant inter-annual difference in CH₄ emissions was found when averaged across straw incorporation and N fertilizer applications for the W2 treatment (42.8 and 15.4?g?m^?2 in 2005 and 2006, respectively). Moreover, N fertilization has no significant effect on CH₄ emissions in this study. Our results demonstrate that although straw effects varied greatly with specific management, both straw managements and water regimes are equally important driving factors and thus being the most promising measures attenuating CH₄ emissions while achieving sustainable rice production.     

Gas emissions from liquid dairy manure: complete versus partial storage emptying

When manure slurry is removed from storages for land application, there is often ‘aged’ manure that remains because the storages are not completely emptied. Aged manure may act as an inoculum and alter subsequent methane (CH₄), nitrous oxide (N₂O) and ammonia (NH₃) emissions when fresh manure is added to the system, compared to an empty storage that is filled with fresh manure. Completely emptying manure storages may be a practice to decrease gas emissions, however, little pilot-scale research has been conducted to directly quantify the inoculum effect. Therefore, we compared CH₄, N₂O, and NH₃ emissions from three pilot-scale slurry tanks (~10.5 m³ each) filled with a mixture of fresh manure and an inoculum of previously stored manure (i.e., partial emptying) to three tanks that contained only fresh manure (i.e., complete emptying). Gas fluxes were continuously measured over 155 d of warm season storage using flow-through steady-state chambers. The absence of an inoculum significantly reduced CH₄ emissions by 56 % compared to partially emptied (inoculated) tanks, while there was no difference in N₂O emissions. There was a significant 49 % reduction in greenhouse gas (GHG) emissions because the overall budget (as CO₂-eq) was dominated by CH₄. Complete manure storage emptying could be an effective GHG mitigation strategy; however, NH₃ emissions were significantly higher from un-inoculated tanks due to slower crust formation. Therefore additional NH₃ abatement should be considered.     

Greenhouse gas intensity and net annual global warming potential of cotton cropping systems in an extremely arid region

A long-term fertilizer experiment investigating cotton-based cropping systems established in 1990 in central Asia was used to quantify the emissions of CO₂, CH₄ and N₂O from April 2012 to April 2013 to better understand greenhouse gas (GHG) emissions and net global warming potential (GWP) in extremely arid croplands. The study involved five treatments: no fertilizer application as a control (CK), balanced fertilizer NPK (NPK), fertilizer NPK plus straw (NPKS), fertilizer NPK plus organic manure (NPKM), and high rates of fertilizer NPK and organic manure (NPKM+). The net ecosystem carbon balance was estimated by the changes in topsoil (0–20 cm) organic carbon (SOC) density over the 22-year period 1990–2012. Manure and fertilizer combination treatments (NPKM and NPKM+) significantly increased CO₂ and slightly increased N₂O emissions during and outside the cotton growing seasons. Neither NPK nor NPKS treatment increased SOC in spite of relatively low CO₂, CH₄ and N₂O fluxes. Treatments involving manure application showed the lowest net annual GWP and GHG intensity (GHGI). However, overuse of manure and fertilizers (NPKM+) did not significantly increase cotton yield (5.3 t ha^?1) but the net annual GWP (?4,535 kg CO₂_eqv. ha^?1) and GHGI (?0.86 kg CO₂_eqv. kg^?1 grain yield of cotton) were significantly lower than in NPKM. NPKS and NPK slightly increased the net annual GWP compared with the control plots. Our study shows that a suitable rate of fertilizer NPK plus manure may be the optimum choice to increase soil carbon sequestration, maintain crop yields, and restrict net annual GWP and GHGI to relatively low levels in extremely arid regions.     

Factors influencing methane emission from peat soils: Comparison of tropical and temperate wetlands

Methane (CH₄) emissions from peat soils in tropical and temperate wetlands were compared. Annual CH₄ emission rates in Ozegahara, the largest wetland on Honshu main island, Japan, were higher than in drained forest wetland areas examined in Indonesia. Methane emissions from the lowland paddy fields examined in Indonesia were higher than those of peaty paddy fields in Japan. There was generally a positive correlation (r² = 0.09; P < 0.1) between CH₄ emissions and CH₄ production activities in wetland soils. In Ozegahara, there was a positive relationship (r² = 0.80; P < 0.01) between CH₄ production activities and soil pH, but there was no such relationship in Indonesia. The range of soil pH in Ozegahara was 5–7, while pH values in the Indonesian sites were lower than 5. There was a positive response of CH₄ emission with respect to groundwater level in all of these areas. In Indonesia, land-use change from swamp and drained forest to cassava or coconut field lowered groundwater levels and decreased CH₄ emission, while change to lowland paddy raised the groundwater level and increased CH₄ emission. Addition of acetate generally inhibited CH₄ production during the early period (until 2 weeks) of incubation, then enhanced it afterward in both Ozegahara and Indonesian wetland soils. Addition of hydrogen mostly enhanced CH₄ production. From the results of this study, CH₄ fluxes from peat soil to the atmosphere were positively correlated with CH₄ production activities, and CH₄ production activity in peat soil was regulated by soil pH, while land-use change from wetland to upland crop lowered groundwater level and thus reduced CH₄ production and enhanced CH₄ oxidation.     

Measurement and modeling of nitrous and nitric oxide emissions from a tea field in subtropical central China

Tea fields represent an important source of nitrous oxide (N₂O) and nitric oxide (NO) emissions due to high nitrogen (N) fertilizer applications and very low soil pH. To investigate the temporal characteristics of N₂O and NO emissions, daily emissions were measured over 2½ years period using static closed-chamber/gas chromatograph and chemiluminescent measurement system in a tea field of subtropical central China. Our results revealed that N₂O and NO fluxes showed similar temporal trends, which were generally driven by temporal variations in soil temperature and soil moisture content and were also affected by fertilization events. The measured average annual N₂O and NO emissions were 10.9 and 3.3 kg N ha^?1 year^?1, respectively, highlighting the high N₂O and NO emissions from tea fields. To improve our understanding of N-cycling processes in tea ecosystems, we developed a new nitrogenous gas emission module for the water and nitrogen management model (WNMM, V2) that simulated daily N₂O and NO fluxes, in which the NO was simulated as being emitted from both nitrification and nitrite chemical decomposition. The results demonstrated that the WNMM captured the general temporal dynamics of N₂O (NSE = 0.40; R² = 0.52, RMSE = 0.03 kg N ha^?1 day^?1, P < 0.001) and NO (NSE = 0.41; R² = 0.44, RMSE = 0.01 kg N ha^?1 day^?1, P < 0.001) emissions. According to the simulation, denitrification was identified as the dominant process contributing 76.5% of the total N₂O emissions, while nitrification and nitrite chemical decomposition accounted for 52.3 and 47.7% of the total NO emissions, respectively.     

Soil CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript>, and N<Subscript>2</Subscript>O fluxes over and between tile drains on corn,soybean, and forage fields under tile drainage management

Controlled tile drainage (CTD) can benefit the environment and crop production. However, CTD has the potential to increase soil greenhouse gas (GHG: CO₂, CH₄, N₂O) emissions by increasing soil water contents and elevating field water levels. A paired-field (CTD and uncontrolled tile drainage (UTD)) approach was used to compare soil GHG emissions for silt loam corn, soybean, and forage fields under CTD and UTD management in eastern Ontario, Canada during a drier and a wetter growing season. A total of five field pairs were examined. Soil GHG emissions directly over tile drains (OT) and between tile drains (BT) in the CTD fields were also assessed. Average soil GHG emissions did not significantly differ (p > 0.05) for CTD and UTD field pairs, except for CO₂ emissions (greater emissions from UTD fields) among two field pairs studied (forage in the drier growing season and soybean in the wetter growing season), and N₂O emissions from a soybean field pair in the wet growing season (greater emissions from CTD field). Significantly higher soil water contents in the UTD forage field may have augmented CO₂ fluxes there. There were some significantly higher N₂O (in the wetter growing season) and CO₂ emissions (in both growing seasons) BT relative to OT locations in some fields; but these differences were not translated significantly to other BT and OT site comparisons. The wetter growing season examined resulted in greater average daily soil CO₂ fluxes overall, but similar CH₄ and N₂O fluxes for soybean fields compared to soybean fields in the drier growing season. Overall, there were no spatially or temporally systematic differences in GHG emissions among CTD and UTD field pairs, or among BT and OT locations in CTD fields.     

Fluxes of methane and nitrous oxide in water-saving rice production in north China

Lowland rice production is currently facing serious water shortages in numerous Asian countries. In the North China Plain water limitations are severe. Water-saving rice production techniques are therefore increasingly searched for. Here we present the first study of trace gas emissions from a water-saving rice production system where soils are mulched and are kept close to field capacity in order to compare their contribution to global warming with traditional paddy rice. In a two-year field experiment close to Beijing, CH₄ and N₂O fluxes were monitored in two forms of the Ground Cover Rice Production System (GCRPS) and in traditional paddy fields using closed chambers. With paddy rice the observed CH₄ emissions were very low, about 0.3 g CH₄ m⁻² a⁻¹ in 2001 and about 1 g CH₄ m⁻² a⁻¹ in 2002. In GCRPS, the CH₄ emissions were negligible. N₂O fluxes in GCRPS were similar, 0.5 to 0.6 g N₂O m⁻² a⁻¹ in 2001 and 2002, and emission peaks mainly followed fertilizer applications. In paddy rice, N₂O fluxes were unexpectedly low throughout the year 2001 (0.03 g N₂O m⁻² a⁻¹), and in 2002 larger emissions occurred during the drainage period. So with 0.4 g N₂O m⁻² a⁻¹ the cumulative flux was similar to emissions in GCRPS. Total CO₂ equivalent fluxes calculated according to IPCC methodology were tenfold higher in GCRPS compared to paddy in 2001. In 2002, fluxes from both systems were similar with 175 and 141 g CO₂ equivalents m⁻² a⁻¹ from GCRPS and paddy. Burkhard Sattelmacher deceased.     

Effect of timing and duration of midseason aeration on CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O emissions from irrigated lowland rice paddies in China

Midseason aeration (MSA) of rice paddy fields functions to mitigate CH₄ emission by a large margin, while simultaneously promoting N₂O emission. Alternation of timing and duration of MSA would affect CH₄ and N₂O emissions from intermittently irrigated rice paddies. A pot trial and a field experiment were conducted to study the effect of timing and duration of MSA on CH₄ and N₂O emissions from irrigated lowland rice paddy soils in China. Four different water regimes, i.e., early aeration, normal aeration (the same as the local practice in timing and duration of aeration), delayed aeration, and prolonged aeration, were adopted separately and compared with respect to global warming potential (GWP) of CH₄ and N₂O emissions and rice yields as well. Total emission of CH₄ from the rice fields ranged from 28.6 to 64.1 kg CH₄ ha⁻¹, while that of N₂O did from 1.71 to 6.30 kg N₂O–N ha⁻¹ during the study periods. Compared with the local practice, early aeration reduced CH₄ emission by 13.3–16.2% and increased N₂O emission by 19.1–68.8%, while delayed aeration reduced N₂O emission by 6.8–26.0% and increased CH₄ emission by 22.1–47.3%. The lowest GWP of CH₄ and N₂O emissions occurred in prolonged aeration treatment, however, rice grain yield was reduced by 15.3% in this condition when compared with normal practice. It was found in the experiments that midseason aeration starting around D 30 after rice transplanting, just like the local practice, would optimize rice yields while simultaneously limiting GWPs of CH₄ and N₂O emissions from irrigated lowland rice fields in China.     

Methane and nitrous oxide emissions from rice paddy soil as influenced by timing of application of hydroquinone and dicyandiamide

A pot trial and a field experiment were conducted to study the effect of timing of application of nitrification inhibitor dicyandiamide (DCD) on N₂O and CH₄ emissions from rice paddy soil. Four treatments including Treatment CK₁, DCD-1 (application of DCD with basal fertilizer), DCD-2 (DCD with tillering fertilizer) and DCD-3 (DCD with panicle initiation fertilizer), were designed and implemented in pot experiment. Total N₂O and CH₄ emissions from DCD-treated soils were decreased profoundly when compared with that from urea alone (P < 0.05). Application of DCD together with basal fertilizer, tillering fertilizer and panicle initiation fertilizer reduced N₂O emission by 8, 30 and 2%, respectively, while those for CH₄ were 21, 8 and 1%. The field experiment with four treatments was carried out subsequently, and a kind of urease inhibitor hydroquinone (HQ) was also incorporated with DCD simultaneously. The combined use of HQ and DCD with basal fertilizer, tillering fertilizer and panicle initiation fertilizer decreased N₂O emissions by 24, 56 and 17%, respectively, while those for CH₄ were 35, 19 and 12%. N₂O emission was effectively reduced by the inhibitor(s) applied with tillering fertilizer before midseason aeration, while CH₄ emission was effectively decreased by the combined use of inhibitor(s) with basal fertilizer before rice transplanting. Furthermore, an increase in rice yield and a reduction of total global warming potential (GWP) of CH₄ and N₂O could be achieved by using inhibitor(s) in rice paddy field.     

Methane (CH4) and nitrous oxide (N2O) emissions from the system of rice intensification (SRI) under a rain-fed lowland rice ecosystem in Cambodia

The present field study investigated the effects of the system of rice intensification (SRI) on greenhouse gas emissions and rice yield, in the first field trial of its kind in Cambodia. The study was a 2 × 4 factorial design, including SRI and conventional management practices (CMP) with the following treatments: control, composted farmyard manure (FYM), mineral fertiliser (MF) and FYM + MF. The results indicated large seasonal variations of CH₄ patterns during the growing season with a peak emission of about 1,300 mg CH₄ m^?2 day^?1 under both production systems 2 weeks after rice transplanting. There was large temporal variability of CH₄ fluxes from morning to midday. Emission of N₂O was below the detection limit in both systems. Under each production system, the highest seasonal emission of CH₄ was under the FYM + MF treatment, namely 282 kg ha^?1 under CMP and 213 kg ha^?1 under SRI. Total CH₄ emission under SRI practices was reduced by 22 % in the FYM treatment, 17 % in the MF treatment and 24 % in the FYM + MF treatment compared to CMP. There was no effect of water management on CH₄ emission in the non-fertilized treatment. Grain yields were not significantly affected by the production system. Thus the yield-scaled global warming potential (GWP) was lower under SRI than CMP, namely 21 % in FYM and FYM + MF treatments, and 8 % in MF treatment. The application of mineral fertilisers moderately increased CH₄ emission but significantly increased rice yields, resulting in a significantly lower yield-scaled-GWP compared to farmyard manure.