Agronomic aspects of wetland rice cultivation and associated methane emissions

Wetland rice cultivation is one of the major sources of atmospheric methane (CH₄). Global rice production may increase by 65% between 1990 and 2025, causing an increase of methane emissions from a 92 Tg CH₄ y^–1 now to 131 Tg in 2025.Methane production depends strongly on the ratio oxidizing: reducing capacity of the soil. It can be influenced by e.g. addition of sulphate, which inhibits methanogenesis. The type and application mode of mineral fertilizers may also affect methane emissions. Addition of organic matter in the form of compost or straw causes an increase of methane emissions, but methane production is lower for materials with a low C/N ratio.High percolation rates in wetland rice soils and occasional drying up of the soil during the cultivation period depresses methane release. Water management practices aimed at reducing emissions are only feasible during specific periods in the rice growing season in flat lowland irrigated areas with high security of water availability and good control of the water supply. Intermittent drying of soils may not be possible on terraced rice lands.Assuming a 10 to 30% reduction in emission rates per unit harvested area, the global emission may amount to 93 Tg CH₄ y^– in 2025. A reduction of global emissions seems very difficult. To develop techniques for reducing CH₄ emissions from wetland rice fields, research is required concerning interactions between soil chemical and physical properties, and soil, water and crop management and methanogenesis. Such techniques should not adversely affect rice yields.     

Spatial and temporal dynamics of methane emissions from agricultural sources in China

Agricultural activities contribute significantly to the global methane budget. Agricultural sources of methane are influenced by land‐use change, including changes in agricultural area, livestock keeping and agricultural management practices. A spatially explicit inventory of methane emissions from agriculture is made for China taking the interconnections between the different agricultural sources into account. The influence of land‐use change on methane emissions is studied by linking a dynamic land‐use change model with emission calculations. The land‐use change model calculates changes in rice area and livestock numbers for a base‐line scenario. Emissions are calculated for 1991 based on land‐use statistics and for 2010 based on simulated changes in land‐use patterns. Emissions from enteric fermentation and manure management are based on emission factors, while emissions from rice paddies involve the calculation of total organic carbon added to rice paddy soils and assume that a constant fraction is emitted as methane. Spatial patterns of emissions are presented for the different sources. For the land‐use scenario considered it is expected that total methane emissions from agricultural sources in China increase by 11% while the relative contribution of rice fields to the emission decreases. Emissions from manure management are expected to become more important. These results indicate that agencies should anticipate changes in source strengths as a consequence of land‐use changes when proposing mitigation strategies and future national greenhouse gas budgets.     

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     

CH4 emissions from rice paddies managed according to farmer's practice in Hunan, China

We measured CH₄ emissions from ricepaddies managed by farmer's practices inChangsha, Hunan Province, China, from 1995 to1997. During the winter season, rice fieldswere left fallow under either drained(C-Fallow) or flooded conditions (C-Flood), andplanted with either Chinese milk vetch (C-GM)or oil-seed rape (C-Rape). The organic manureproduced in the winter (weeds, Chinese milkvetch, or oil-seed rape straw) was incorporatedin situ before the early-ricetransplanting. Both early-rice and late-ricestraws were removed and the soil was notamended with any exogenous organic manure. For1996 to 1997, the average seasonal CH₄emission for the double rice cropping periodwas the highest from the plot that was floodedin the winter (103.5 g CH₄ m^–2) andlowest from the plot planted and incorporatedwith Chinese milk vetch (32.6 gCH₄ m^–2). Precipitation in the winternot only affected growth of green manure, whichwas incorporated in situ, but might alsoaffect CH₄ emissions during the subsequentrice growing period. Therefore, a simplerelationship could not be found between theincorporated amount of green manure andCH₄ emission. In the plots incorporatedwith vetch and oil-seed rape straw CH₄emissions were significantly less during thesubsequent late-rice period than during theearly-rice period. This phenomenon might beattributed to a ``priming effect' of greenmanure, which exhausted soil labile organicmatter. Based on the CH₄ fluxmeasurements, the total CH₄ emissions fromrice fields in Hunan Province during the ricegrowing season were estimated as 1.56 TgCH₄ in 1996 and 1.06 Tg CH₄ in 1997.Large variation of precipitation in the winterwould be an important factor controlling theannual variation of CH₄ emissions from thetreatments.     

Role of rice in mediating methane emission

Methane emitted at different plant conditions through the different organs of rice plants was studied using a closed chamber technique under the laboratory, phytotron, and greenhouse conditions in order to clarify and quantify the role of different organs of rice plant as methane emission sites. Rice plants grown in flooded soils emit methane to the atmosphere via the aerenchyma of leaves, nodes and panicles. Emission through the rice plants is controlled by diffusion. No methane is emitted via the transpiration stream. Leaves are the major release sites at the early growth stage while nodes become more important later. Cracks and porous structure were found in the nodes. Panicles generally contribute little to methane emission. Increasing water depth temporarily reduces methane emission while concentration gradients in rice plants readjust to unsubmerged emission sites. Methane emissions in rice plants cease only when the plants become totally submerged.     

Effects of ammonium-based fertilisation on microbialprocesses involved in methane emission from soilsplanted with rice

The emission of the greenhouse gas CH₄ from ricepaddies is strongly influenced by management practicessuch as the input of ammonium-based fertilisers. Weassessed the impact of different levels (200 and 400kgN.ha^–1) of urea and (NH₄)₂HPO₄on the microbial processes involved in production andconsumption of CH₄ in rice field soil. We usedcompartmented microcosms which received fertilisertwice weekly. Potential CH₄ production rates weresubstantially higher in the rice rhizosphere than inunrooted soil, but were not affected by fertilisation.However, CH₄ emission was reduced by the additionof fertiliser and was negatively correlated with porewater NH ₄ ^plus concentration, probably as theconsequence of elevated CH₄ oxidation due tofertilisation. CH₄ oxidation as well as numbersof methanotrophs was distinctly stimulated by theaddition of fertiliser and by the presence of the riceplant. Without fertiliser addition,nitrogen-limitation of the methanotrophs will restrictthe consumption of CH₄. This may have a majorimpact on the global CH₄ budget, asnitrogen-limiting conditions will be the normalsituation in the rice rhizosphere. Elevated potentialnitrifying activities and numbers were only detectedin microcosms fertilised with urea. However, asubstantial part of the nitrification potential in therhizosphere of rice was attributed to the activity ofmethanotrophs, as was demonstrated using theinhibitors CH₃F and C₂H₂.     

Spatial distribution of methane-oxidizing activity in a flooded rice soil

In a study on spatial distribution of methane oxidation in an unplanted flooded field, methane-oxidizing activity, analysed in soil samples under laboratory conditions, decreased with increasing depth (25 cm and beyond). In a flooded field planted to rice, rates of methane oxidation followed the order : rhizosphere (collected from roots at 10-20 cm depth) > surface soil at (0-1 cm) > subsurface soil at 10-20 cm depth, diagonally 10-15 cm away from the centre of hill. Application of ammonium sulfate and, to a lesser extent, urea to surface, rhizosphere and subsurface soil samples from flooded field planted to rice effected a distinct inhibition of methane oxidation. Nitrification inhibitors (thiourea, sodium thiosulfate and dicyandiamide) were also effective in inhibiting methane oxidation. Both surface and rhizosphere soil samples harbored higher populations of methane-oxidizing bacteria than the subsurface soil. Inhibition of methane oxidation in surface and rhizosphere soil samples concomitant with the suppression of autotrophic ammonium oxidizers by nitrification inhibitors implicates an active involvement of autotrophic ammonium oxidizers in methane oxidation.     

Development of region-specific emission factors and estimation of methane emission from rice fields in the East, Southeast and South Asian countries

Rice cultivation areas in East, Southeast and South Asia account for 89% of the world total, and field measurements of methane (CH₄) emission from rice cultivation have been widely performed in this area. In this paper, we assembled most of the measurements and developed region‐specific CH₄ emission factors. Efforts were made in order to regionalize rice fields by climate and soil properties, and to incorporate the effect of organic input and water regime on emission. Data on rice cultivation areas of 1995 were collected at subdivision level (province, state, prefecture, etc.). Total emission from these areas was estimated at 25.1 Tg CH₄ year ^{? 1}, of which 7.67 Tg was emitted from China and 5.88 Tg from India. Irrigated and rainfed rice fields contributed 70.4 and 27.5% to the total emission, respectively. Deepwater rice fields had a very small share. A high‐resolution and quality emission distribution map was constructed as the emission was directly estimated at province level and below that, a 30‐second land‐use dataset was used in order to translate the emission to grid format. As the rice cultivation area in the study region accounts for 89% of the world total, extrapolating the estimate to the global scale indicates a global emission of 28.2 Tg CH₄ year ^{? 1}. The estimate was compared with country reports made by local scientists. For some countries – such as Indonesia, Myanmar, Thailand, Vietnam, Japan, South Korea, Pakistan and the Philippines – the results of this estimate agree reasonably well with their country reports (CV < 15%). For some other countries – such as China, India and Bangladesh – there is relatively large disagreement between our estimate and their country reports. The reasons for the discrepancies were discussed.     

西双版纳热带人工雨林生物量及净第一性生产力的研究

通过标准木法和收获法研究分析了西双版纳热带人工模拟雨林的生物量及净第一性生产力.结果表明,林分总生物量约为390.4t·hm^-2,其中乔木层生物量达362.5t·hm^-2,占总生物量的92.8%,灌木层生物量为19.3t·hm^-2,占4.9%,层间植物(包括附生植物)的生物量为3.6t·hm^-2,草本层生物量为5.0t·hm^-2.分别占1.3%和0.9%.林分净第一性生产力为2227.3g·m^-2.年^-1,其中乔木层的净生产力为1553.5g·m^-2.年^-1,占整个林分净生产力的69.7%,灌木层、草本层及层间植物分别仅占26.9%、2.4%和1.0%.其器官分配比例以茎最高,达42.0%;其次为叶,占30.2%;枝仅占13.5%.叶面积指数为7.061.同时建立了林分优势种及乔木层各器官生物量的优化回归模型.     

猪粪与沼气渣对双季稻田甲烷排放的影响

随着环境温度的升高,稻田甲烷排放通量增加。早稻期间甲烷排放通量随着水稻生育期的增加而逐步加快,而晚稻甲烷排放主要集中在水稻生长的前中期,而且排放量很高。一天中甲烷排放具有很强的周期性,在6：00～8：00时,甲烷排放通量进入谷底,14：00时甲烷排放通量达到峰值。稻田甲烷排放通量与土壤5cm处的温度及土壤水溶解甲烷含量具有较高的相关性。猪粪和沼气渣的施用分别提高稻田甲烷排放量22．14％和4．40％。在早稻期间,施用猪粪和沼气渣分别提高土壤水溶解甲烷含量40．3％和11．9％,而晚稻期间仅分别提高23．9％和5．04％。     

Assessment of the methane mitigation potentials of alternative water regimes in rice fields using a process‐based biogeochemistry model

Rice production is a substantial source of atmospheric CH₄, which is second only to CO₂ as a contributor to global warming. Since CH₄ is produced in anaerobic soil environments, water management is expected to be a practical measure to mitigate CH₄ emissions. In this study, we used a process‐based biogeochemistry model (DNDC‐Rice) to assess the CH₄ mitigation potentials of alternative water regimes (AWR) for rice fields at a regional scale. Before regional application, we tested DNDC‐Rice using site‐scale data from three rice fields in Japan with different water regimes. The observed CH₄ emissions were reduced by drainage of the fields, but were enhanced by organic amendments. DNDC‐Rice gave acceptable predictions of variation in daily CH₄ fluxes and seasonal CH₄ emissions due to changes in the water regime. For regional application, we constructed a GIS database at a 1 × 1 km mesh scale that contained data on rice field area, soil properties, daily weather, and farming management of each cell in the mesh, covering 3.2% of the rice fields in Japan's Hokkaido region. We ran DNDC‐Rice to simulate CH₄ emissions under five simulated water regimes: the conventional water regime and four AWR scenarios with gradually increasing drainage. We found that AWR can reduce CH₄ emission by up to 41% compared with the emission under conventional water regime. Including the changes in CO₂ and nitrous oxide emissions, potential mitigation of greenhouse gas (GHG) was 2.6 Mg CO₂ Eq. ha^?1 yr^?1. If this estimate is expanded to Japan's total rice fields, expected GHG mitigation is 4.3 Tg CO₂ Eq. yr^?1, which accounts for 0.32% of total GHG emissions from Japan. For a reliable national‐scale assessment, however, databases on soil, weather, and farming management must be constructed at a national scale, as these factors are widely variable between regions in Japan.     

Effect of gas pressure in the root and stem base zone on methane transport through rice bodies

Ebullition of gas bubbles from the soil surface is, in some cases (e.g., in early growth stage of rice), one of the major pathways for methane transport from rice paddies to the atmosphere. However, the role of the gas phase (entrapped gas) in the paddy soil in plant-mediated methane transport, which is the major pathway for methane emission, has not been clarified. To clarify the effect of the gas phase below ground on the methane emission rate through rice plants, we partly exposed the root and stem base of hydroponically grown rice to a high concentration of methane gas at various gas pressures, and immersed the rest of the roots in a solution with a high methane concentration. The methane emission rate was measured from the top of the rice plant using a flow-through chamber method. The methane emission rate drastically increased with a small increase in gas pressure in the gas phase at the root and stem base zone, with about a 3 times larger emission rate being observed with 10 × 10^-3 atm of extra pressure (corresponding to 10 cm of standing water in rice paddy) compared to no extra pressure. However, when alginate was applied to the stem near the base to prevent contact with the gas phase, the methane emission rate did not increase with increasing gas pressure. On the other hand, from observations in the rice paddy, it was found that the gas is entrapped near the surface (e.g., at a depth of 1 cm) and the gas entrapped in the soil would come into direct contact with a part of the stem near the base of the rice plant. Thus, the gas entrapped in the soil could enter into the rice body directly from the part of the stem near the base which is beneath the soil surface due to gas pressure in the gas phase resulting from the pressure exerted by the standing water. Hence, this mechanism involving the entrapped gas could play an important role in methane emission from rice paddy by affecting the plant-mediated methane transport as well as ebullition of gas bubbles.     

不同施肥方式对稻麦轮作田土壤杂草种子库的影响

为揭示不同施肥方式(纯施化肥、有机肥配施化肥、秸秆还田配施有机无机肥、有机无机复合肥)对稻麦两熟制地区农田土壤杂草种子库的影响, 在江苏常州金坛区进行了固定施肥试验。经过连续4年试验处理后, 对不同施肥处理下农田土壤杂草种子库杂草种子种类及密度进行了调查, 并对杂草种子多样性、数量、分布与施肥措施的关系进行了分析。结果表明, 与不施肥相比, 施肥有减少稻麦轮作田土壤杂草种子库杂草种子种类数、杂草种子群落均匀度指数和物种多样性指数的趋势, 并使稻麦轮作田土壤杂草种子库杂草种子总密度明显降低。施肥明显提高了土壤杂草种子库菵草(Beckmannia syzigachne)、日本看麦娘(Alopecurus japonicus)、看麦娘(A. aequalis)种子的密度, 施用猪粪堆肥配施化肥处理提高程度更为显著; 秸秆还田配施化肥、秸秆还田配施有机肥化肥、有机无机复合肥施用处理有减少菵草、日本看麦娘、看麦娘杂草种子密度的趋势。施肥明显降低了土壤杂草种子库阔叶杂草种子密度; 施用有机肥有增加土壤杂草种子库水苦荬(Veronica undulata)、蛇床(Cnidium monnieri)种子密度的趋势; 施用猪粪堆肥有增加土壤杂草种子库鸭舌草(Monochoria vaginalis)种子密度的趋势。因此, 不同种类杂草对不同肥料存在偏好性差异, 不同施肥方式造成了土壤杂草种子库优势物种组成的差异。     

减磷配施有机肥对水旱轮作紫色水稻土磷素淋失的消减效应

为探索长江流域稻油轮作系统水稻季减少农田磷素流失的最佳施肥模式和有效耕作措施,降低其对长江水质的威胁。采用渗漏池长期田间原位定点试验并结合室内实验分析,研究了化肥配施猪粪有机肥和水稻秸秆还田对土壤磷素淋溶迁移的影响。结果表明在水稻生长期内土壤淋溶水中磷素浓度随时间延长呈逐渐下降的趋势,前期波动幅度大且下降迅速,到55d之后逐步稳定达到平衡。总可溶性磷(TDP)是渗漏水磷素的主要形态。土壤淋溶水中总磷(TP)和总可溶性磷(TDP)含量均表现为优化施肥+猪粪有机肥(MP)优化施肥+秸秆还田(SP)优化施肥(P)优化施肥量磷减20%+猪粪有机肥(MDP)优化施肥量磷减20%+秸秆还田(SDP)不施磷肥(P0)。土壤总磷(TP)淋失负荷在0.295—0.493 kg/hm2之间。施用有机肥提高了淋溶水中的磷素含量,促进了土壤中磷素的淋失,同时显著提高了土壤中有效磷的含量,猪粪有机肥的促进作用比水稻秸秆大。减少化肥施用量有利于降低土壤磷素淋失。在综合考虑农业生产省本增效和控制农田面源污染的情况下,可以采取减量化肥配施有机肥的施肥模式。     

铁炉渣施加对稻田甲烷产生、氧化与排放的影响

为了阐明铁炉渣施加对稻田甲烷产生、氧化与排放的影响,采用静态箱-气相色谱法对对照(CK)、2 Mg/hm2(FeⅠ)、4Mg/hm2(FeⅡ)和8 Mg/hm2(FeⅢ)铁炉渣施加后稻田甲烷产生、氧化与排放进行了测定与分析.研究结果表明:观测期内,CK、Fe Ⅰ、FeⅡ和FeⅢ样地甲烷产生量分别为0.06-8.87、0.12-8.28、0.15-7.84、0.17-7.82 mg·m-2·h-1,平均产生量分别为4.68、3.92、3.14、2.76 mg·m-2·h-1;甲烷氧化量分别是0.02-1.27、0.09-0.95、0.09-1.54、0.09-2.79 mg·m-2·h-1,平均氧化量为0.46、0.47、0.59、0.55 mg·m-2·h-1;甲烷排放分别是0.04-7.99、0.03-7.33、0.06-6.30、0.08-5.12 mg· m-2·h-1,平均值分别为3.11、2.29、1.76、1.59 mg·m-2·h-1.铁炉渣的施加降低了甲烷产生量和排放通量,提高了甲烷氧化量.     

Do nitrogen fertilizers stimulate or inhibit methane emissions from rice fields?

In rice cultivation, there are controversial reports on net impacts of nitrogen (N) fertilizers on methane (CH ₄) emissions. Nitrogen fertilizers increase crop growth as well as alter CH ₄ producing (Methanogens) and consuming (Methanotrophs) microbes, and thereby produce complex effects on CH ₄ emissions. Objectives of this study were to determine net impact of N fertilizers on CH ₄ emissions and to identify their underlying mechanisms in the rice soils. Database was obtained from 33 published papers that contained CH ₄ emissions observations from N fertilizer (28–406 kg N ha^?1) treatment and its control. Results have indicated that N fertilizers increased CH ₄ emissions in 98 of 155 data pairs in rice soils. Response of CH ₄ emissions per kg N fertilizer was significantly (P < 0.05) greater at < 140 kg N ha^?1 than > 140 kg N ha^?1 indicating that substrate switch from CH ₄ to ammonia by Methanotrophs may not be a dominant mechanism for increased CH ₄ emissions. On the contrary, decreased CH ₄ emission in intermittent drainage by N fertilizers has suggested the stimulation of Methanotrophs in rice soils. Effects of N fertilizer stimulated Methanotrophs in reducing CH ₄ emissions were modified by the continuous flood irrigation due to limitation of oxygen to Methanotrophs. Greater response of CH ₄ emissions per kg N fertilizer in urea than ammonia sulfate probably indicated the interference of sulfate in the CH ₄ production process. Overall, response of CH ₄ emissions to N fertilizers was correlated with N‐induced crop yield (r = +0.39; P < 0.01), probably due to increased carbon substrates for Methanogens. Using CH ₄ emission observations, this meta‐analysis has identified dominant microbial processes that control net effects of N fertilizers on CH ₄ emissions in rice soils. Finally, we have provided a conceptual model that included microbial processes and controlling factors to predict effects of N fertilizers on CH ₄ emissions in rice soils.     

减氮配施有机肥对滴灌棉田土壤生物学性状与团聚体特性的影响

本文通过新疆绿洲棉田连续4年定位施肥试验,研究了不同处理[对照CK、常规化肥CF、减氮配施普通有机肥OF(80%CF+OF和60%CF+OF)、减氮配施生物有机肥BF(80%CF+BF和60%CF+BF)]对土壤生物学性状和团聚体特性的影响,探讨了土壤生物学性状与有机碳及团聚体之间的关系.结果表明:与单施化肥(CF)相比,配施生物有机肥的80%CF+BF和60%CF+BF处理均可显著提高土壤脲酶、碱性磷酸酶、蔗糖酶、β-葡萄糖苷酶、多酚氧化酶和芳基硫酸酯酶活性,其增幅分别为55.6%～84.0%、53.1%～74.0%、15.1%～38.0%、38.2%～68.0%、29.6%～52.0%和35.4%～58.9%,高量配施有机肥效果优于低量配施.各施肥处理明显提高了土壤基础呼吸,具体表现为BF>OF>CF>CK.与CF相比,60%CF+BF处理的土壤有机碳、微生物生物量碳分别增加22.3%和43.5%,但微生物生物量碳氮比显著下降.>0.25 mm的水稳性团聚体在配施普通有机肥的80%CF+OF、60%CF+OF处理比对照(CK)分别增加7.1%和8.0%.80%CF+BF处理较80%CF+OF处理机械稳定性团聚体的几何平均直径(GMD)增加了9.2%.冗余(RDA)分析和聚类分析均表明,减氮增碳可明显调控滴灌棉田土壤生物活性与团聚体结构.连续4年化肥减量配施有机肥或生物有机肥,提高了土壤有机碳含量,并对团聚体稳定性和生物学性状有协同改善效应,是维持与提升绿洲滴灌棉田土壤肥力的有效途径.     

东北黑土地区稻田甲烷排放时空演变及排放潜力分析

稻田甲烷排放是农业源甲烷排放的主要来源。东北黑土地区是我国最大的粮食生产基地,农业温室气体减排是实现黑土地永续利用的关键议题之一。运用稻田甲烷排放模型（CH4MOD）核算并分析了2009—2018年东北黑土地区稻田甲烷排放的时空演变特征,结合GOSAT卫星遥感数据探究了水稻生产与区域甲烷排放的时空动态联系,进一步量化了稻田甲烷对区域甲烷排放的贡献程度及不同情景下的排放潜力。结果表明,受水稻生产面积扩张和排放强度提高的影响,东北黑土地区稻田甲烷排放总量从2009年的39.05万t增加到2018年的79.53万t。东北黑土地区区域甲烷排放在季节变化和栅格单元上表现出与稻田甲烷排放较为一致的时空动态,大规模的稻田耕作可能会增加水稻生产与区域甲烷排放直接相关的可能性。随着水稻持续扩种稳产,2018年东北黑土地区水稻生产贡献了区域甲烷排放总量的15.04%,其中黑龙江省的贡献率高达31.06%。在基准发展情景下,预计2035年东北黑土地区稻田CH₄排放量较2018年增加19.5%;在粮食供给保障情景下,维持当前稻田耕作面积,水稻生产集约化程度提高,预计其稻田CH₄排放量较2018年减少0.88%;在此基础上,采取促进秸秆还田、增施有机肥、实施节水间歇灌溉等稻田管理措施将使稻田CH₄排放量增加17.8%—63.6%。以满足膳食需求和供给保障为导向,优化水稻种植结构、控制稻田耕作面积,推动技术进步、品种改良以提升单产水平,采取化肥和有机肥搭配施用、节水间歇灌溉等途径能够缓解稻田甲烷排放。研究综合运用自上而下的遥感数据和自下而上的模型运算,刻画了水稻生产与区域甲烷排放的时空联系,进一步评估了稻田甲烷的排放潜力及减排措施的减排效果,为促进东北黑土地区农业甲烷减排和生产布局优化提供了理论依据和决策参考。     

控释氮肥对抗除草剂转基因水稻田土壤甲烷排放的影响

采用温室盆栽和静态箱-气相色谱法,研究了控释氮肥对抗除草剂转基因水稻和亲本常规水稻稻田土壤甲烷(CH4)排放的影响。供试土壤为潴育型水稻土,氮肥种类为尿素和控释氮肥。结果表明,与对照(尿素)相比,控释氮肥提高了水稻分蘖数、株高、生物量及产量。水稻品种对CH4季节性排放规律没有明显影响,CH4排放通量基本表现为,自水稻移栽后逐渐升高,移栽后62—92 d出现峰值,而后逐渐降低至水稻收获。与对照相比,控释氮肥可显著降低CH4排放通量和全生育期累积排放量。抗除草剂转基因水稻稻田土壤CH4排放通量和累积排放量均显著低于亲本常规水稻。研究认为,一次性基施控释氮肥和种植抗除草剂转基因水稻对有效减缓稻田甲烷排放具有重要意义。