Potassium application reduces methane emission from a flooded field planted to rice

In a field study, potassium (K) applied as muriate of potash (MOP) significantly reduced methane (CH₄) emission from a flooded alluvial soil planted to rice. Cumulative emission was highest in control plots (125.34 kg CH₄ ha⁻¹), while the lowest emission was recorded in field plots receiving 30 kg K ha⁻¹ (63.81 kg CH₄ ha⁻¹), with a 49% reduction in CH₄ emission. Potassium application prevented a drop in the redox potential and reduced the contents of active reducing substances and Fe²⁺ content in the rhizosphere soil. Potassium amendment also inhibited methanogenic bacteria and stimulated methanotrophic bacterial population. Results suggest that, apart form producing higher plant biomass (both above- and underground) and grain yield, K amendment can effectively reduce CH₄ emission from flooded soil and could be developed into an effective mitigation option, especially in K-deficient soils.     

Methane-oxidizing activities and methanotrophic populations associated with wetland rice plants

Acetylene up to 500 μl l^–1 did not affect methane formation in anoxic soil up to 12 h, but further incubation for 1 week showed strong inhibition of methanogenesis. To ascertain the extent of the oxidation of methane produced from rice-planted pots, the effect of acetylene on methane emission was studied. Two rice varieties (Toyohatamochi and Yamahikari) were grown in a greenhouse in submerged soil in pots. At about maximum tillering, heading, and grain-forming stages, methane fluxes were measured. Flux measurement was performed for 3 h from 6 pm, then acetylene at 100 μl l^–1 was added to some of the pots. At 6 a.m. the following day, methane fluxes were again measured for 3 h. Only at maximum tillering stage of the variety Toyohatamochi was a significant increase (1.4 times) in methane flux caused by acetylene observed, whereas in the other treatments no significant increase in methane fluxes by acetylene could be defected. To ascertain the activity of methane monooxygenase (MMO), propylene oxide (PPO) formation from propylene was measured with excised roots and a basal portion of stems of the rice plants grown on the submerged soil. A level of 0.1–0.2 μmol PPO h^–1 plant^–1 was recorded. The roots showed the highest PPO formation per gram dry matter, followed by basal stems. Methane oxidation was roughly proportional to PPO formation. Soluble MMO-positive methanotroph populations were measured by plate counts. The number of colony-forming units per gram dry matter was 10⁶–10⁵ in roots, and 10⁴–10³ in basal stems. These results indicate the possibility of methane oxidation in association with wetland rice plants. Received: 26 October 1995     

Greenhouse gas emissions from farmed organic soils: a review

Abstract. The large boreal peatland ecosystems sequester carbon and nitrogen from the atmosphere due to a low oxygen pressure in waterlogged peat. Consequently they are sinks for CO₂ and strong emitters of CH₄. Drainage and cultivation of peatlands allows oxygen to enter the soil, which initiates decomposition of the stored organic material, and in turn CO₂ and N₂O emissions increase while CH₄ emissions decrease. Compared to undrained peat, draining of organic soils for agricultural purposes increases the emissions of greenhouse gases (CO₂, CH₄, and N₂O) by roughly 1t CO₂ equivalents/ha per year. Although farmed organic soils in most European countries represent a minor part of the total agricultural area, these soils contribute significantly to national greenhouse gas budgets. Consequently, farmed organic soils are potential targets for policy makers in search of socially acceptable and economically cost-efficient measures to mitigate climate gas emissions from agriculture. Despite a scarcity of knowledge about greenhouse gas emissions from these soils, this paper addresses the emissions and possible control of the three greenhouse gases by different managements of organic soils. More precise information is needed regarding the present trace gas fluxes from these soils, as well as predictions of future emissions under alternative management regimes, before any definite policies can be devised.     

Methane mitigation in flooded Louisiana rice fields

Summary A field experiment was conducted to determine whether selected nitrification inhibitors (encapsulated calcium carbide and dicyandiamide) and SO _inf4 ^sup-2 -containing compounds [(NH₄)₂SO₄ and Na₂SO₄] had mitigating effects on CH₄ emissions from flooded rice. Microplots were established within a rice bay drill-seeded with the Texmont rice cultivar and CH₄ fluxes were measured over the main rice cropping season. Methane emissions over the 77-day sampling period were approximately 230, 240, 260, 290, 310, and 360 kg CH₄ ha^-1 from the calcium carbide, Na₂SO₄-rate II, Na₂SO₄-rate I, (NH₄)₂SO₄, dicyandiamide, and urea (control) treatments, respectively. Reductions in CH₄ evolution, compared to the control, ranged from 14 to 35%, depending on treatment. The selected inhibitors and SO _inf4 ^sup-2 -containing compounds appear to be effective in reducing the CH₄ emitted from flooded rice fields.     

Influence of the insecticide carbofuran on the production and oxidation of methane in a flooded rice soil

Applications of a commercial formulation of carbofuran, a carbamate insecticide, at rates of 2kg and 12kg active ingredient ha^–1 to flooded fields planted to rice led to significant inhibition of methane emission. Likewise, laboratory incubation studies showed that carbofuran applied at low rates (5 and 10μgg^–1soil) inhibited the net methane production relative to that of the control, but stimulated it when applied at a rate of 100μgg^–1soil. Interestingly, carbofuran increased the oxidation of methane when applied at low rates and inhibited it when applied at a rate of 100μgg^–1soil. Received: 5 May 1997     

Fluxes of methane from rice fields and potential for mitigation

Abstract. Methane (CH₄) is an important greenhouse gas. Flooded rice fields (paddies) are a significant source of atmospheric CH₄; estimates of the annual emission from paddies range from less than 20 to 100 million Tg, with best estimates of 50 × 20 Tg. The emission is the net result of opposing bacterial processes: production in anaerobic microenvironments, and consumption and oxidation in aerobic microenvironments, both of which occur sequentially and concurrently in flooded rice soils. With current technologies, CH₄ emission from rice fields will increase as production increases. Over the next 25 years rice production will have to increase by 65% from the present 460 Mt/y to 760 Mt/y in 2020. The current understanding of the processes controlling CH₄ fluxes, rice growth and rice production is sufficient to develop mitigation technologies. Promising candidates are changes in water management, rice cultivars, fertilization, and cultural practices. A significant reduction of CH₄ emission from rice fields, at the same time that rice production and productivity increase at the farm level, is feasible, although the regions where particular practices can be applied, and the trade-offs that are possible, have still to be identified.     

长期施肥对湖南稻田甲烷排放的影响

采用静态箱-气相色谱法对长期不同施肥处理的稻田甲烷排放进行了手动观测。结果表明，不同施肥处理的稻田甲烷排放具有一致的规律，混施有机肥的处理甲烷排放大于单施氮肥的处理，同施用稻草相比，发酵猪粪处理的甲烷排放较少。文章还对影响稻田甲烷排放的因素进行了讨论。     

Effect of silicate fertilizer on reducing methane emission during rice cultivation

Slag-type silicate fertilizer, which contains high amount of active iron oxide, a potential source of electron acceptor, was applied at the rate of 0, 2, 6, 10, and 20 Mg ha⁻¹ to reduce methane (CH₄) emission from rice planted in potted soils. Methane emission rates measured by closed chamber method decreased significantly with increasing levels of silicate fertilizer application during rice cultivation. Soil redox potential (Eh) decreased rapidly after flooding, but floodwater pH and soil pH increased significantly with increasing levels of silicate fertilizer application. Iron concentrations in potted soils and in percolated water significantly increased with the increasing levels of silicate fertilizer application, which acted as oxidizing agents and electron acceptors, and thereby suppressed CH₄ emissions. Silicate fertilization significantly decreased CH₄ production activity, while it increased carbon dioxide (CO₂) production activity. Rice plant growth, yield parameters, and grain yield were positively influenced by silicate application levels. The maximum increase in grain yield (17% yield increase over the control) was found with 10 Mg ha⁻¹ silicate application along with 28% reduction in total CH₄ flux during rice cultivation. It is, therefore, concluded that slag-type silicate fertilizer could be a suitable soil amendment for reducing CH₄ emissions as well as sustaining rice productivity and restoring the soil nutrient balance in rice paddy soil.     

Methane emission from paddy fields in Taiwan

 In order to investigate the effect of environmental conditions on CH₄ emission from paddy fields in Taiwan, four locations, two cropping seasons and two irrigation systems were studied. CH₄ emission was high at the active tillering and the booting stages in the first cropping season, whereas it was low at the transplanting and the ripening stages with an intermittent irrigation system. CH₄ emission was high at the transplanting stage in the second cropping season, and decreased gradually during rice cultivation. Daily temperature and light intensity increased gradually during rice growth in the first cropping season (February–June), while it was reversed in the second cropping season (August–December). The seasonal CH₄ emission from paddy fields ranged from 1.73 to 11.70 g m^–2, and from 10.54 to 39.50 g m^–2 in the first and second cropping seasons, respectively. The seasonal CH₄ emission in the second cropping season was higher than that in the first cropping season in all test fields. The seasonal CH₄ emission was 32.65 mg m^–2 in the first cropping season of the National Taiwan University paddy field with continuous flooding, and it was 28.85 mg m^–2 in the second cropping season. The annual CH₄ emission ranged from 12.3 to 49.3 g m^–2 with an intermittent irrigation system, and the value was 61.5 g m^–2 with a continuous flooding treatment. The annual CH₄ emission from paddy fields was estimated to be 0.034 Tg in 1997 from 364,212 ha of paddy fields with an intermittent irrigation system, which was less than the 0.241 Tg calculated by the IPCC method with a continuous flooding treatment Received: 23 February 2000     

Methane production in unamended and rice-straw-amended soil at different moisture levels

 CH₄ production in an alluvial soil, unamended or amended with rice straw (1% w/w), was examined under nonflooded [–1.5 MPa, –0.01 MPa and 0 MPa (saturated) and flooded (1 : 1.25 soil to water ratio)] conditions during a 40-day incubation in closed Vacutainer tubes. CH₄ production was negligible at –1.5 MPa, but increased with an increase in the moisture level. Addition of rice straw distinctly increased CH₄ production in the soil at all moisture levels including –1.5 MPa. Evidence, in terms of the drop in redox potential and Fe²⁺ accumulated, suggested that the addition of rice straw hastened the reduction of the soil, even under nonflooded conditions; thus its addition stimulated even the nonflooded soil to produce CH₄ in substantial amounts. Our results indicate that many currently unidentified sources of CH₄, possibly including organic-amended nonflooded soils, may make a significant contribution to the global CH₄ budget. Received: 10 July 1997     

Fluxes of methane and carbon dioxide from soil under forest, grazing land, irrigated rice and rainfed field crops in a watershed of Nepal

Field evolution of CH₄ and CO₂ from soils under four dominant land uses in the Mardi watershed, western Nepal, were monitored at 15-day intervals for 1 year using closed chamber techniques. The CH₄ oxidation rate (mean±SE, g CH₄ m^–2 h^–1) in the forest (22.8±6) was significantly higher than under grazing land (14±2) and an upland rainfed maize and millet system (Bari) (2.6±0.9). Irrigated rice fields (Khet) showed an oxidation rate of 6±0.8 g CH₄ m^–2 h^–1 in the dry season (December–May) but emitted a mean rate of 131 g CH₄ m^–2 h^–1 in the rainy season and autumn (June–October). The evolution of CO₂ ranged from 10 mg CO₂ m^–2 h^–1 in the Bari in January to 1,610 mg CO₂ m^–2 h^–1 in the forest in July. Higher evolution of CO₂ (mean±SE, mg CO₂ m^–2 h^–1) was observed in the Bari (399±39) and forest (357±36) compared to Khet (246±25) and grazing (206±20) lands. The annual emission of CO₂ evolution varied from 86.6 to 1,836 g CO₂ m^–2 year^–1. The activation energy for CH₄ and CO₂ varied between 16–283 and 80–117 kJ mol^–1, respectively. The estimated temperature coefficient for CO₂ emission varied from 2.5 to 5.0. Temperature explained 46–51% of the variation in CO₂ evolution, whereas it explained only 4–36% of the variation in CH₄ evolution.     

An approach to soil testing with special reference to the zinc requirement of rice paddy soils

Abstract

Experiments were conducted to seek a better basis for soil testing of rice paddy soils. Soils were incubated under variable conditions of simulated flooding, and then extracted with DTPA⁵ . The amounts of Cu, Zn, Mn and Fe extracted were sensitive to the imposed soil conditions. Good correlations between Zn extracted from simulated flooded soils and Zn uptakes by rice from flooded soils in pots, suggest that this approach to soil testing may be more useful for paddy soils than existing tests on air dried soils.     

Effect of continuous and alternate water regimes on methane efflux from rice under greenhouse conditions

In a greenhouse study, the effect of moisture regimes (continuously flooded, continuously nonflooded, alternately flooded) on methane efflux from an alluvial soil planted to rice was studied using the closed chamber method. Methane efflux was almost 10 times more pronounced under continuously flooded conditions than under continuously nonflooded conditions. Intermittently flooded regimes (alternately flooded and nonflooded cycles of 40 or 20 days each) emitted distinctly less methane than the continuously flooded system. A significant negative correlation was found between methane emission under different water regimes and rhizosphere redox potential. Extractable Fe²⁺, readily mineralizable carbon (RMC) and root biomass presented a significant positive correlation with cumulative methane emission. The correlation of methane emission with other plant parameters and microbial biomass was not significant. Our results further suggest the possibility of reduced methane emissions through appropriate water management in a rainfed rice ecosystem. Received: 4 June 1996     

Effects of Sesbania rostrata and Azolla microphylla incorporation on transformation of applied zinc and copper in lateritic rice soils with different flooding regimes

Fixation of Zn and Cu applied to tropical rice-growing lateritic soils rich in Fe-oxides may be reduced if the soils are kept flooded for a few days before their application. There may be a further reduction if such flooding is combined with incorporation of green manures. To investigate this effect, a laboratory experiment was conducted to study the effect of different periods (0 and 15 days) of preflooding combined with (0 and 0.50% of soil weight) Sesbania rostrata and Azolla microphylla incorporation as green manures on the transformation of applied Zn and Cu in two lateritic rice-growing soils. Recovery of added Zn/Cu in DTPA (diethylene triamine pentaacetate)-extractable form was always found to be higher when they were applied after the soils were maintained in a flooded state for 15 days than when applied immediately after flooding; this effect was more prominent in respect of Cu. Contrary to expectations, green manure incorporation along with preflooding caused a significant decrease in recovery of Zn/Cu; the effect, however, showed a decreasing trend as incubation progressed. The effect was more marked with A. microphylla than with S. rostrata, particularly with Cu. Possible causes of such changes and their implications on the Zn/Cu nutrition of rice are discussed. Received: 7 August 1995     

Response of rice to increasing nitrogen rates in five soils with different mineralizable nitrogen levels

Rice is one of the essential foods of the human diet and advances in agronomic crop management, such as nitrogen (N) rate management, can improve productivity and profitability and reduce adverse environmental impacts. Nitrogen fertilization rates in Chile are generally based on crop yield without considering the soil's capacity to supply it. Five rice soils of the Inceptisol, Alfisol, and Vertisol orders in central Chile were incubated at 20°C for 21 d in the 2011–2012 season, and their N mineralization capacity was determined before sowing the rice crop. These soils were cropped in field conditions with rice fertilized with 0, 80, and 160 kg N ha^?1; grain yield, harvest index, and grain sterility were determined. Mineralized N was associated with some chemical properties of each soil, and with the response to N rates in grain yield and grain sterility. Results indicated that the N rates to be used in rice must consider soil N mineralization capacity and crop yield potential. Finally, the best response to the N rates used in this study and the effect on both harvest index and grain sterility was achieved with 80 kg N ha^?1.     

水稻土基底呼吸与CO2排放强度的日动态及长期不同施肥下的变化

土壤呼吸排放是陆地生态系统土气交换快速而活跃的途径之一,对大气CO2浓度的变化有显著的影响。本文对太湖地区一个代表性水稻土水稻收割后土壤基底呼吸CO2排放进行了昼夜观测和采样分析。结果表明,不同小区平均土壤呼吸与CO2排放速率在CO2-C.12.2～25.2.mg/(m2h)之间,日排放量在CO2-C.327.2～604.1mg/(m2d)之间,低于文献报道的森林和草地及旱作农田的土壤呼吸;与长期有机-无机配施处理相比,长期单施化肥CO2日排放量提高了55%～85%,并且显著提高了土壤呼吸对土壤(5.cm)温度的响应敏感性。相关分析表明,土壤呼吸CO2排放强度与土壤微生物N(Nmic)、微生物C∶N(Cmic/Nmic)和P的有效性有密切的关系;生物有效N和P的有效性显著地影响着土壤呼吸与CO2的生成和排放。本试验结果进一步支持了水稻土的固碳效应。但是,供试不同小区土壤呼吸排放强度的变异隐含着长期不同施肥处理可能使与高呼吸活性有关的微生物群落发生改变,有待于进一步研究。     

Effect of wax-coated calcium carbide and nitrapyrin on nitrogen loss and methane emission from dry-seeded flooded rice

Summary The effectiveness of wax-coated calcium carbide (as a slow-release source of acetylene) and nitrapyrin in inhibiting nitrification and emission of the greenhouse gases N₂O and CH₄ was evaluated in a microplot study with dry-seeded flooded rice grown on a grey clay near Griffith, NSW, Australia. The treatments consisted of factorial combinations of N levels with nitrification inhibitors (control, wax-coated calcium carbide, and nitrapyrin). The rate of nitrification was slowed considerably by the addition of wax-coated calcium carbide, but it was inhibited only slightly by the addition of nitrapyrin. As a result, the emission of N₂O was markedly reduced by the application of wax-coated calcium carbide, whereas there was no significant difference in rates of N₂O emission between the control and nitrapyrin treatments. Both nitrification inhibitors significantly reduced CH₄ emission, but the lowest emission rates were observed in the wax-coated calcium carbide treatment. At the end of the experiment 84% of the applied N was recovered from the wax-coated calcium carbide treatment compared with 43% for the nitrapyrin and control treatments.     

CO2 emission from soils under different uses and flooding conditions

The emission of CO₂ from Galician (NW Spain) forest, grassland and cropped soils was studied in a laboratory experiment, at different temperatures (10-35 °C) and at moisture contents of 100% and 160% of the field capacity (FC) of each soil (the latter value corresponds to saturated conditions, and represents between 120% and 140% of the water holding capacity, depending on the soil). In the forest soil, respiration in the flooded samples at all temperatures was lower than that at 100% field capacity. In the agricultural (grassland and cropped) soils the emission was higher (particularly at the highest incubation temperatures) in the soils wetted to 160% of the field capacity than in those wetted to 100% of the field capacity. In all cases the emission followed first order kinetics and the mineralization constants increased exponentially with temperature. In the forest soil, the Q₁₀ values were almost the same in the soils incubated at the two moisture contents. The grassland and cropped soils displayed different responses, as the Q₁₀ values were higher in the soils at 160% than in those at 100% of field capacity. In addition, and particularly at the highest temperatures, the rate of respiration increased sharply 9 and 17 days after the start of the incubation in the grassland and in the cropped soil, respectively. The above-mentioned anomalous response of the grassland and cropped soils under flooding conditions may be related to the agricultural use of the soils and possibly to the intense use of organic fertilizers in these soils (more than 150 kg N ha⁻¹ year⁻¹ added as cattle slurry or manure, respectively, in the grassland and cropped soils). The observed increase in respiration may either be related to the development of thermophilic facultative anaerobic microbes or to the formation during the incubation period of a readily metabolizable substrate, possibly originating from the remains of organic fertilizers, made accessible by physicochemical processes that occurred during incubation under conditions of high moisture.