秸秆还田对中国农田土壤温室气体排放的影响

为了更好地了解和掌握秸秆还田对中国农田土壤温室气体排放的影响,笔者根据历年国内相关文献,就秸秆还田对中国农田土壤CO2、N2O和CH4等主要温室气体排放的影响进行较全面的综述。研究表明：秸秆还田能增加农田土壤CO2和CH4的排放通量,对N2O排放通量的影响表现为不确定性,分析了秸秆还田对农田土壤温室气体排放的影响因素,探讨了该领域存在的问题及未来的研究方向。秸秆还田对中国农田土壤温室气体排放有一定影响,对各温室气体影响程度和影响机理不同。     

保护性耕作对黄土高原旱地春小麦成熟期农田温室气体通量日变化的影响

为了预测农田生态系统中CO2、N2O、CH4的排放对全球气候变暖的响应,及其温度对温室气体排放日变化的影响,利用CO2分析仪、静态箱-气象色谱法,对黄土高原旱区农田生态系统传统耕作(T)和保护性耕作(NTS)措施下春小麦成熟期CO2、N2O、CH4气体通量日变化进行原位观测。结果表明：2种耕作措施下农田土壤均表现为大气CO2、N2O的源和CH4的汇。CO2、N2O、CH4都有明显的日变化特征,传统耕作措施下CO2排放通量明显高于保护性耕作。CO2日排放通量最高峰出现在12:00,最低峰出现在2:00。N2O日排放最高峰出现在16:00,最低峰出现在0:00。保护性耕作措施能增加农田土壤N2O通量的排放。2种耕作措施下CH4吸收通量的最高峰均出现在14:00,保护性耕作措施下CH4吸收通量的最低峰出现在22:00,传统耕作措施则出现在2:00。采取保护性耕作措施能促进农田土壤对CH4通量的吸收。地表温度,5 cm地温与CO2排放通量都有极显著的正相关关系,且都与CO2通呈指数函数关系。N2O与各个耕层的土壤温度都有极显著的正相关关系,且与N2O排放通量呈线性函数关系。2种耕作措施下,CO2通量与地表温度的相关系数最高,N2O与10 cm地温的相关系数最高。CH4与地表温度具有极显著的负相关关系。     

耕作与秸秆还田方式对稻田N2O排放、水稻氮吸收及产量的影响

保护性耕作是改善农田土壤肥力的重要举措,然而其对作物氮吸收与产量的作用尚不明确。为此,本试验于2016—2017年稻季在湖北省武穴市花桥镇,设置常规翻耕与免耕两种耕作方式以及前茬作物秸秆全量还田与不还田两种秸秆还田方法,研究耕作与秸秆还田方式对稻田土壤N2O排放、根系酶活性、水稻氮吸收与产量的影响。结果表明,耕作方式显著影响土壤N2O排放,但不影响根系硝酸还原酶与谷氨酰胺合成酶活性、水稻氮吸收与产量。与翻耕处理相比,免耕处理2016年和2017年土壤N2O排放量分别显著提高了12.5%~18.2%和21.1%~38.6%。秸秆还田显著影响土壤N2O排放量、根系酶活性、水稻氮吸收与产量。相对于秸秆不还田处理,秸秆还田处理2016年和2017年土壤N2O排放量分别显著提高了38.5%~45.5%和13.1%~29.5%。秸秆还田处理相对于不还田处理根系硝酸还原酶与谷氨酰胺合成酶活性分别显著增加了6.7%~45.9%和9.0%~46.7%,水稻氮吸收量提高了12.5%~26.0%,产量增加了9.4%~12.6%。本文认为,虽然秸秆还田提高了水稻氮吸收与产量,但也促进了土壤N2O的排放,因此在评估保护性耕作稻田温室效应时应加强对温室气体(CH4和N2O)排放和土壤碳固定影响的长期监测,以期为发展低碳稻作提供理论依据和技术支撑。     

生物炭对稻田温室气体CH4和N2O排放的影响综述

稻田是大气CH4和N2O的重要排放源,减少稻田CH4和N2O排放对缓解全球气候变暖具有重要意义。生物炭具有含碳量高、难分解、比表面积大、疏松多孔等特性。利用生物炭可改善稻田土壤理化性质及微生物学性质,减少温室气体的排放,提高水稻产量。在现有相关研究的基础上,结合国内外研究进展,回顾了国内外生物炭的研究历史及特性,全面评述了生物炭影响稻田温室气体排放的作用机理,以及对稻田温室气体CH4和N2O排放、综合温室效应(GWP)、温室气体排放强度(GHGI)、净生态系统经济预算(NEEB)的影响等国内外研究进展,提出了未来生物炭在稻田温室气体排放方面的研究方向。     

生物炭对CH_4和N_2O排放的影响综述

稻田是大气CH4和N2O的重要排放源,减少稻田CH4和N2O排放对缓解全球气候变暖具有重要意义。生物炭具有含碳量高、难分解、比表面积大、疏松多孔等特性。利用生物炭可改善稻田土壤理化性质及微生物学性质,减少温室气体的排放,提高水稻产量。在现有相关研究的基础上,结合国内外研究进展,回顾了国内外生物炭的研究历史及特性,全面评述了生物炭影响稻田温室气体排放的作用机理,以及对稻田温室气体CH4和N2O排放、综合温室效应(GWP)、温室气体排放强度(GHGI)、净生态系统经济预算(NEEB)的影响等国内外研究进展,提出了未来生物炭在稻田温室气体排放方面的研究方向。     

农田温室气体N2O排放研究进展

N2O是重要的温室气体之一,1mol N2O的温室效应是CO2的150～200倍.在提倡发展“农业现代化即机械化+化学化”的模式下,农业已然成为温室气体排放的第二大排放源.综述了农田N2O的产生机制以及影响农田土壤N2O排放的相关因素,同时从对土壤养分控制的角度入手提出了相应的减排措施.     

生物炭对土壤N2O和CH4排放影响的研究进展

为了探讨生物炭对土壤N2O和CH4排放影响的途径和机理,在综合评述前人研究的基础上,就生物炭对土壤N2O和CH4排放的影响因素、途径和影响机理进行了分析,提出了不同土壤的生物炭施用原则,并指出了今后生物炭研究应注意的问题:(1)明确土壤中2种温室气体排放特点,园地制宜地选择合适的生物炭类型;(2)注意生物炭的添加时机和用量;(3)目前学者所用的生物炭类型以及土壤种类不同,关于生物炭影响土壤N2O和CH4排放的研究结论不同.在这方面的研究工作还应在完善生物炭施用标准的基础上,继续进行生物炭还田的本地化试验验证,才能为生物炭对土壤N2O和CH4排放的影响得出更明确的结论.     

保护性耕作对农田温室效应的影响研究进展

以耕作和秸秆利用对温室气体排放的影响为重点,简述了当前温室气体排放的研究方法及保护性耕作所产生的温室效应,提出了农田温室气体排放研究方法的主导方向,明确了保护性耕作的温室效应不是免耕与秸秆还田所产生的相对温室效应的简单累加,发展新型保护性耕作技术以及对其温室效应的研究是未来保护性耕作研究的重点     

秸秆还田对土壤氮磷及水土的影响研究

秸秆还田作为低碳农业、有机农业的重要环节,对改善土壤结构,减少水土流失,提高土壤的养分含量具有积极作用。秸秆还田主要通过增加土壤孔隙度,降低土壤容重从而调节地温,达到蓄水保墒的功能,促进作物生长。秸秆还田能有效增加土壤有机质含量,提高氮肥的利用效率,有效减少氮素、磷素的流失,提高土壤氮素的含量,对土壤中有效磷和全磷含量均有所提高,改善农田生产环境,保障粮食增产能力。秸秆还田能有效减少地表径流量和径流次数,从而减少径流所带走的养分,减缓对周围水系的面源污染,有利于提高土壤含水量。有效的秸秆还田对N2O等温室气体的排放的实验研究,有着不同的研究结果。但是秸秆还田的实施还存在着一定的问题,应进一步深入研究秸秆还田对土壤养分和环境的影响机制,进行长期监测实验,发展恰当的秸秆还田方式,减少化肥的使用,对促进我国农业的持续快速发展有着十分重要的意义。     

农业生态系统中氮素反硝化作用与N2O排放研究进展

硝化-反硝化作用是土壤氮素循环的两个重要环节,在其生物化学过程中产生的N2O和N2,不但会引起氮素损失,降低氮肥利用率,还会增加大气中的温室气体浓度,带来环境危害。因此,无论是从农业的观点,还是从环境的角度看,硝化反硝化作用已引起人们越来越多的关注。本文根据近年来国内外的文献资料,阐述了各个农业生态系统的硝化反硝化损失和N2O排放量,介绍了减少硝化反硝化损失和N2O排放的措施,并对今后的研究工作提出建议。     

Conservation Agriculture practices reduce the global warming potential of rainfed low N input semi-arid agriculture

Conservation tillage and crop rotations improve soil quality. However, the impact of these practices on greenhouse gas (GHG) emissions and crop yields is not well defined, particularly in dry climates. A rainfed 2-year field-experiment was conducted to evaluate the effect of three long-term (17–18 years) tillage systems (Conventional Tillage (CT), Minimum Tillage (MT) and No Tillage (NT)) and two cropping systems (rotational wheat (Triticum aestivum L.) preceded by fallow, and wheat in monoculture), on nitrous oxide (N₂O) and methane (CH₄) emissions, during two field campaigns. Soil mineral N, water-filled pore space, dissolved organic carbon (C) and grain yield were measured and yield-scaled N₂O emissions, N surplus and Global Warming Potentials (GWP) were calculated. No tillage only decreased cumulative N₂O losses (compared to MT/CT) during campaign 1 (the driest campaign with least fertilizer N input), while tillage did not affect CH₄ oxidation. The GWP demonstrated that the enhancement of C stocks under NT caused this tillage management to decrease overall CO₂ equivalent emissions. Monoculture increased N₂O fluxes during campaign 2 (normal year and conventional N input) and decreased CH₄ uptake, as opposed to rotational wheat. Conversely, wheat in monoculture tended to increase soil organic C stocks and therefore resulted in a lower GWP, but differences were not statistically significant. Grain yields were strongly influenced by climatic variability. The NT and CT treatments yielded most during the dry and the normal campaign, and the yield-scaled N₂O emissions followed the same tendency. Minimum tillage was not an adequate tillage management considering the GWP and the yield-scaled N₂O emissions (which were 39% lower in NT with respect to MT). Regarding the crop effect, wheat in rotation resulted in a 32% increase in grain yield and 31% mitigation of yield-scaled N₂O emissions. Low cumulative N₂O fluxes (<250 g N₂O-N ha⁻¹ campaign⁻¹) highlighted the relevance of soil organic C and CO₂ emissions from inputs and operations in rainfed semi-arid cropping systems. This study suggests that NT and crop rotation can be recommended as good agricultural practices in order to establish an optimal balance between GHGs fluxes, GWP, yield-scaled N₂O emissions and N surpluses.     

尿素及秸秆添加对华中地区茶园土壤CO_2和N_2O排放的影响

为了明确尿素和秸秆添加对茶园土壤CO_2和N2O排放的影响,为茶园合理施肥提供理论依据,本研究在室内培养条件下,以华中地区红壤丘陵区茶园土壤为对象,运用静态培养系统研究方法,研究该土壤在尿素输入和作物秸秆添加后CO_2和N_2O的排放特征。培养试验共设置对照、尿素、作物秸秆和尿素+作物秸秆4种处理。结果表明:不同处理下华中地区茶园土壤CO_2和N_2O排放呈显著差异。作物秸秆添加显著提高茶园土壤CO_2的排放,作物秸秆和作物秸秆+尿素处理分别是对照的5.57和4.99倍。尿素输入显著促进茶园土壤N_2O的排放,而秸秆添加却降低N_2O的排放。对照和添加尿素处理土壤N_2O排放通量与铵态氮含量呈显著正相关关系。无秸秆添加处理土壤N_2O排放通量与硝态氮含量呈显著的相关性,而添加秸秆处理二者无显著相关关系。土壤可溶性有机碳含量对CO_2排放有显著影响,二者之间呈极显著线性正相关关系。     

Effects of irrigation and nitrogen fertilization on the greenhouse gas emissions of a cropping system on a sandy soil in northeast Germany

Irrigation induces processes that may either decrease or increase greenhouse gas emissions from cropping systems. To estimate the net effect of irrigation on the greenhouse gas emissions, it is necessary to consider changes in the crop yields, the content of soil organic carbon and nitrous oxide emissions, as well as in emissions from the use and production of machinery and auxiliary materials. In this study the net greenhouse gas emissions of a cropping system on a sandy soil in northeast Germany were calculated based on a long-term field experiment coupled with two-year N₂O flux measurements on selected plots. The cropping system comprised a rotation of potato, winter wheat, winter oil seed rape, winter rye and cocksfoot each under three nitrogen (N) fertilization intensities with and without irrigation. Total greenhouse gas emissions ranged from 452 to 3503 kg CO_2-eq ha⁻¹ and 0.09 to 1.81 kg CO_2-eq kg⁻¹ yield. Application of an adequate amount of N fertilizer led to a decrease in greenhouse gas emissions compared to zero N fertilization whereas excessive N fertilization did not result in a further decrease. Under N fertilization there were no significant differences between irrigation and non-irrigation. Increases in greenhouse gas emissions from the operation, production and maintenance of irrigation equipment were mainly offset by increases in crop yield and soil organic carbon contents. Thus, on a sandy soil under climatic conditions of north-east Germany it is possible to produce higher yields under irrigation without an increase in the yield-related greenhouse gas emissions.     

The new nitrification inhibitor 3,4-dimethylpyrazole succinic (DMPSA) as an alternative to DMPP for reducing N2O emissions from wheat crops under humid Mediterranean conditions

Nowadays agricultural practices are based in the use of N fertilizers which can lead to environmental N losses. These losses can occur as nitrous oxide (N₂O) emissions as result of the microbial processes of nitrification and denitrification. N₂O together with carbon dioxide (CO₂) and methane (CH₄) are the strongest greenhouse gases (GHG) associated with agricultural soils. Nitrification inhibitors (NI) have been developed with the aim of decreasing fertilizer-induced N losses and increasing N efficiency. One of the most popular NI is the 3,4-dimethylpyrazol phosphate (DMPP) which have proven to be an advisable strategy to mitigate GHG emissions while maintaining crops yield. A new NI, 3,4-dimethylpyrazole succinic (DMPSA), has been developed. The objective of this study was to compare the impact of the new nitrification inhibitor DMPSA on greenhouse gases emissions, wheat yield and grain protein with respect to DMPP. For this purpose a field-experiment was carried out for two years. Fertilizer dose, with and without NIs, was 180 kg N ha⁻¹ applied as ammonium sulphate (AS) split in two applications of 60 kg N ha⁻¹ and 120 kg N ha⁻¹, respectively. A single application of 180 kg N ha⁻¹ of AS with NIs was also made. An unfertilized treatment was also included. The new nitrification inhibitor DMPSA reduces N₂O emissions up to levels of the unfertilized control treatment maintaining the yield and its components. The DMPSA shows the same behavior as DMPP in relation to N₂O fluxes, as well as wheat yield and quality. In spite of applying a double dose of N at stem elongation than at tillering, N₂O losses from that period are lower than at tillering as a consequence of the influence of soil water content and temperature reducing the N₂O/N₂ ratio by denitrification. NI efficiency in reducing N₂O losses is determined by the magnitude of the losses from the AS treatment.     

Mitigating N2O emissions from cropping systems after conversion from pasture − a modelling approach

Converting pasture to cropping is common in many of the world’s agricultural systems. This conversion results in substantial net mineralisation of soil organic matter that builds up during a phase of pasture. A few studies have shown that this mineralisation leads to increased nitrous oxide (N₂O) emissions compared to long-term pasture or long-term cropping. Understanding of interactions leading to these significant emissions is still scarce but is needed to identify mitigation options for this situation. In this study, the Agricultural Production Systems sIMulator (APSIM) was used to investigate the optimal timing of pasture termination (relative to crop planting) and management of nitrogen (N) in crops after pasture termination to maximise crop yield and limit N₂O emissions. Beforehand, APSIM’s performance in simulating yields and N₂O emissions was tested against data from field experiments conducted in the temperate high-rainfall zone of southern Australia where N₂O emissions were monitored with automatic gas collection chambers during the first year of cropping wheat after terminating long-term pasture on two adjacent sites in two consecutive years. Field experiments and simulation scenarios showed very high N₂O emissions (up to 48 kg N₂O-N ha⁻¹ yr⁻¹) in the first year of wheat after pasture termination, even without N fertiliser application. Measured cumulative N₂O emissions, crop yields and soil mineral N and water content dynamics were simulated well with APSIM. Including a routine into APSIM to account for N₂O transport through the soil profile improved the simulation of daily N₂O emissions considerably, leading to up to 67% of the measured variability in daily N₂O emissions being explained by the model. We predicted that a short fallow between termination of pasture and sowing wheat, instead of a long fallow which is the common practice, reduces N₂O emissions by more than half in the first year of cropping without a noteworthy impact on crop yield. Reducing N fertiliser applications in the first few years after pasture termination by taking available soil mineral N into account, and applying the fertiliser six to twelve weeks after sowing instead of at sowing was predicted to further reduce N₂O emissions. Since the model was calibrated against experimental data during the first year after pasture termination only, experiments determining N₂O emissions in the first two or three years after terminating pasture are needed to confirm our predictions.     

Decreased foliar nitrogen and crop yield in organic rainfed almond trees during transition from reduced tillage to no-tillage in a dryland farming system

Sustainable farming practices can be beneficial or detrimental to crop production in the short-term, which will strongly determine their appeal to farmers. We evaluated the effects of several sustainable practices on soil properties, plant nutrition and ecophysiology and crop yield in a semiarid agroecosystem. A three-year randomised experiment was conducted in a rainfed almond grove where the initial soil management was reduced tillage. Two alternative treatments were evaluated: reduced tillage plus green manure and no-tillage. The following soil and plant parameters were measured once per year: soil organic carbon, total nitrogen and P_olsen; foliar N, P, δ¹³C and δ¹⁵N and crop yield. We found that soil bulk density increased significantly with no-tillage. Leaf δ¹⁵N was positively associated with soil fertility, foliar nutrient concentrations and crop yield across treatments. Leaf δ¹³C, N_foliar and crop yield were strongly positively associated across treatments in every year of the study. Reduced tillage treatments displayed higher leaf δ¹⁵N, δ¹³C, N_foliar and crop yield than the no-tillage treatment, indicating a sharp decrease in the leaf nitrogen status and intrinsic water use efficiency of almond trees during the transition from reduced tillage to no-tillage. In semiarid agroecosystems where soils are prone to compaction, some tillage is required to maintain optimal crop production in rainfed almonds.     

Application of DNDC model to estimate N<Subscript>2</Subscript>O emissions from green tea fields in Japan

Heavy doses of N fertilizers are commonly applied to green tea fields in Japan, and cause large amount of nitrate leaching in ground water and emission of ammonia and nitrous oxide (N₂O) to the atmosphere. The Denitrification and Decomposition (DNDC) model was tested against experimental data on N₂O emissions from the tea field in Nishio, Aichi, Japan. There were reasonable agreements between the simulated and measured values of N₂O emissions for this site. The model was then applied for estimating the environmental impacts as affected by farm management practices, climate change, and soil properties. The model results were assessed with respect to major indicators of agro-ecosystems including crop yield, soil organic carbon sequestration, nitrate leaching loss, and N₂O emission. The results indicated that use of compost significantly reduced nitrate leaching and N₂O emissions in comparison with N fertilizer. When soil pH and texture shifted to non-acidic and coarser soil, N₂O emission increased; and a change in temperature and precipitation affected N₂O emission, nitrate leaching, and SOC sequestration. This study thus revealed the biogeochemistry model as a powerful tool in addressing the complex efficacy of the alternative farm management practices in tea fields across various climate and soil conditions.     

Dense planting with less basal nitrogen fertilization might benefit rice cropping for high yield with less environmental impacts

Dense planting and less basal nitrogen (N) fertilization have been recommended to further increase rice (Oryza sativa L.) grain yield and N use efficiency (NUE), respectively. The objective of this study was to evaluate the integrative impacts of dense planting with reduced basal N application (DR) on rice yield, NUE and greenhouse gas (GHG) emissions. Field experiments with one conventional sparse planting (CK) and four treatments of dense planting (increased seedlings per hill) with less basal N application were conducted in northeast China from 2012 to 2013. In addition, a two-factor experiment was conducted to isolate the effect of planting density and basal N rate on CH₄ emission in 2013. Our results show that an increase in planting density by about 50% with a correspondingly reduction in basal N rate by about 30% (DR1 and DR2) enhanced NUE by 14.3–50.6% and rice grain yield by 0.5–7.4% over CK. Meanwhile, DR1 and DR2 reduced GWP by 6.4–12.6% and yield-scaled GWP by 7.0–17.0% over CK. According to the two-factor experiment, soil CH₄ production and oxidation and CH₄ emission were not affected by planting density. However, reduced basal N rate decreased CH₄ emission due to it significantly reduced soil CH₄ production with a smaller reduction in soil CH₄ oxidation. The above results indicate that moderate dense planting with less basal N application might be an environment friendly mode for rice cropping for high yield and NUE with less GHG emissions.     

N2O-Freisetzung auf gemähtem Dauergrünland in Abhängigkeit von Standort und N-Düngung

N₂O Emissions from True Meadows Dependent on Location and N Fertilization Agricultural production is thought to be a main anthropogenic emitter of nitrous oxide (N₂O), which contributes to global warming and the destruction of the ozone layer. There is still considerable uncertainty about the amount of N₂O emission, and the site‐specific parameters that affect N₂O emission. From October 1995 until March 1998 experiments were conducted at established field plots (true meadows) at three different sites, i.e. low mountain range (Eifel), lowland (Niederrhein), and moist meadows (Münsterland). Plots were fertilized with calcium ammonium nitrate (CAN) at nitrogen equivalents ranging from 0 to 360 kg N ha^–1. N₂O fluxes were measured throughout the whole year using the closed‐chamber method. In addition, data on temperature, water‐filled pore space and precipitation were collected. N₂O emission rates (mg N₂O‐N ha^–1 h^–1) were highest either after fertilizer application or in winter during frost, depending on the experimental site and N dosage. The annual amount of N losses due to N₂O emission was dependent on the experimental site and the type and dosage of fertilizer. Disregarding the 360 kg N ha^–1 level of the CAN treatments, the N losses in this experiment were less than 1.5 kg N₂O‐N ha^–1 yr^–1. At low fertilizer dosage there was no reliable correlation between the amount of N that was applied and the amount of N₂O that was emitted. However, with high fertilizer levels the N₂O emissions increased gradually. Finally, N₂O emissions were more influenced by the amount of CAN than by the site.     

Effects of different manuring systems with and without biogas digestion on soil mineral nitrogen content and on gaseous nitrogen losses (ammonia,nitrous oxides)

Nitrogen (N) is the most susceptible nutrient to transformations affecting plant availability. These transformations include mineralization, immobilization, nitrification and denitrification, as well as leaching and ammonia volatilization. Use of stable wastes and other residues for biogas digestion may reduce N-losses. It is the purpose of this paper (i) to assess the effects of biogas digestion on soil mineral N (SMN) content in spring and autumn, (ii) to compare NH₃ volatilization following superficial application of different manures to a cereal crop, (iii) to compare greenhouse gas emissions of differently treated liquid slurry after its application via injection into closed slots, and (iv) to compare greenhouse gas emissions of differing manuring treatments within a whole organic stockless cropping system. The SMN content in autumn was not influenced by digestion of slurry. However, if cover crops and crop residues were harvested for digestion instead of leaving it on the field, a strong decrease of the SMN content was measured. Ammonia volatilization after application from digested slurry was higher than the volatilization from undigested slurry, likely due to the effect of the higher ammonia content and higher pH. Organic manuring by application of liquid effluents of the biogas digester, by incorporation of green manures with a narrow C/N ratio or by mulching aboveground biomass of a clover/grass-ley, resulted in a strong increase in N₂O emissions. The balance showed a 38% decrease in N₂O emissions for a whole arable organic stockless cropping system when crop residues and the clover/grass-ley were harvested, digested, and the effluents were reallocated within the same cropping system, in comparison to mulching and incorporation of the biomass as green manure. Injection of liquid cattle slurry resulted in a strong increase of N₂O emissions. The results provide some evidence that denitrification during nitrification was the driving force for the measured emission peaks. It was concluded, that biogas digestion of field residues resulted in a win-win situation, with additional energy yields, a lower nitrate leaching risk and lower nitrous oxide emissions. However, the propensity to ammonia volatilization was higher in digested manures.