农业土壤中的氧化亚氮排放: 为减排综述时空变化

This short review deals with soils as an important source of the greenhouse gas N2O. The production and consumption of N2O in soils mainly involve biotic processes: the anaerobic process of denitrification and the aerobic process of nitrification. The factors that significantly influence agricultural N2O emissions mainly concern the agricultural practices (N application rate, crop type, fertilizer type) and soil conditions (soil moisture, soil organic C content, soil pH and texture). Large variability of N2O fluxes is known to occur both at different spatial and temporal scales. Currently new techniques could help to improve the capture of the spatial variability. Continuous measurement systems with automatic chambers could also help to capture temporal variability and consequently to improve quantification of N2O emissions by soils. Some attempts for mitigating soil N2O emissions, either by modifying agricultural practices or by managing soil microbial functioning taking into account the origin of the soil N2O emission variability, are reviewed.     

Mitigating nitrous oxide emissions from a maize-cropping black soil in northeast China by a combination of reducing chemical N fertilizer application and applying manure in autumn

Abstract

Nitrous oxide (N₂O) emissions from agricultural soils, mainly caused by chemical nitrogen (N) fertilizer inputs, are major sources of N₂O in Chinese terrestrial ecosystems. Thus, attempts to reduce N₂O emissions from agricultural soils by optimizing N applications are receiving increasing attention. Further, organic fertilizers are being increasingly used in China to improve crop production/quality and prevent or reduce soil degradation. However, organic and chemical fertilizers are often both applied in spring in northeast China, which promotes N₂O emissions and may be sub-optimal. Therefore, we hypothesized that reducing applications of chemical fertilizer N and applying manure in autumn could be an effective strategy for mitigating N₂O emissions from cropped soils in the region. To test this hypothesis, we established a field trial to investigate the effects of different combinations of chemical N fertilizer applications and animal manure in autumn on both N₂O emissions and maize (Zea mays L.) grain yields in northeast China. The treatments, expressed as NxMy (where Nx and My denote the total amounts of chemical fertilizer nitrogen (N) and manure (M) applied in kg N ha^?1 and m³ M ha^?1, respectively), were N₀M₀, N₂₃₀M₀, N₂₇₀M₁₂, N₂₃₀M₁₅, N₃₂₀M₁₈ in 2010 and N₀M₀, N₂₃₀M₀, N₂₀₀M₁₂, N₂₀₀M₁₅, N₂₈₀M₁₈ in 2011. Measurements of the resulting N₂O emissions showed that pulse fluxes occurred after each chemical N fertilizer application, but not after manure inputs in autumn or during soil-thawing periods in the following spring. Emission factors for the chemical fertilizer N were on average 1.07% (1.00?1.10%) and 1.14% (0.49?1.83%) in 2010 and 2011, respectively. Furthermore, by comparing the nine pairs of fertilization treatments, the relative increase in cumulative nitrous oxide-nitrogen (N₂O-N) emissions was found to be proportional to the relative increase in urea application, but independent of the amount of autumn-applied manure. These findings imply that N₂O emissions from fertilized agricultural soils in northeast China could be mitigated by supplying manure in the autumn and reducing the total amount of chemical N fertilizer applied in the following year. Although no significant difference in maize grain yield was found among the fertilization treatments, the grain yield-scaled N₂O emissions for the treatments with a lower chemical N application (e.g., N₂₃₀M₁₅ and N₂₀₀M₁₅ treatments) were significantly lower than those with a higher chemical N application (e.g., N₃₂₀M₁₈ and N₂₈₀M₁₈ treatments). Meanwhile, under the condition of the same application amount of chemical fertilizer N, the grain yield-scaled N₂O emission decreased with the increase of manure application rate. Thus, the results support the hypothesis that combining reductions in chemical N fertilizer and applying manure in autumn could be an effective strategy for mitigating N₂O emissions from N-fertilized soils in northeast China.     

Nitrous oxide emissions from wetland soil amended with inorganic and organic fertilizers

Agricultural soils are a primary source of anthropogenic trace gas emissions, and the subtropics contribute greatly, particularly since 51% of world soils are in these climate zones. A field experiment was carried out in an ephemeral wetland in central Zimbabwe in order to determine the effect of cattle manure (1.36% N) and mineral N fertilizer (ammonium nitrate, 34.5% N) application on N₂O fluxes from soil. Combined applications of 0 kg N fertilizer + 0 Mg cattle manure ha^?1 (control), 100 kg N fertilizer + 15 Mg manure ha^?1 and 200 kg N fertilizer + 30 Mg manure ha^?1 constituted the three treatments arranged in a randomized complete block design with four replications. Tomato and rape crops were grown in rotation over a period of two seasons. Emissions of N₂O were sampled using the static chamber technique. Increasing N fertilizer and manure application rates from low to high rates increased the N₂O fluxes by 37–106%. When low and high rates were applied to the tomato and rape crops, 0.51%, 0.40%, and 0.93%, 0.64% of applied N was lost as N₂O, respectively. This implies that rape production has a greater N₂O emitting potential than the production of tomatoes in wetlands.     

有机无机肥配施对酸性菜地土壤硝化作用的影响

通过室内培养和田间试验, 研究了有机无机肥配施对酸性菜地土硝化作用的影响。培养试验条件为60%土壤最大持水量和25 ℃。 结果表明,土壤硝化作用模式为指数方程,延滞期10天。与纯化肥处理（NPK）相比,鲜猪粪配施无机肥（FPM+NPK）和猪粪堆肥配施无机肥（CPM+NPK）均能降低土壤硝化势和氨氧化潜势,猪粪堆肥配施无机肥还能增加土壤微生物量碳、 氮。鲜猪粪配施无机肥和猪粪堆肥配施无机肥处理在硝化培养和田间试验期间N2O释放量均没有差异,但硝化培养期间鲜猪粪配施无机肥的N2O释放量显著低于纯化肥处理,田间试验期间猪粪堆肥配施无机肥的N2O释放量显著低于纯化肥处理。培养试验结束后的土壤pH值与土壤硝化势间,以及硝化培养期间N2O累积释放量与土壤硝化势间均存在显著正相关关系。本研究表明, 有机无机肥配施显著影响土壤硝化作用以及硝化培养期间和田间N2O释放。     

Microbial communities, biomass, and activities in soils as affected by freeze thaw cycles

Two Finnish agricultural soils (peat soil and loamy sand) were exposed to four freeze-thaw cycles (FTC), with a temperature change from −17.3±0.4 °C to +4.1±0.4 °C. Control cores from both soils were kept at constant temperature (+6.6±2.0 °C) without FTCs. Soil N₂O and CO₂ emissions were monitored during soil thawing, and the effects of FTCs on soil microbes were studied. N₂O emissions were extremely low in peat soil, possibly due to low soil water content. Loamy sand had high N₂O emission, with the highest emission after the second FTC. Soil freeze-thaw increased anaerobic respiration in both soil types during the first 3-4 FTCs, and this increase was higher in the peat soil. The microbial community structure and biomass analysed with lipid biomarkers (phospholipid fatty acids, 3- and 2- hydroxy fatty acids) were not affected by freezing-thawing cycles, nor was soil microbial biomass carbon (MIB-C). Molecular analysis of the microbial community structure with temperature gradient gel electrophoresis (TGGE) also showed no changes due the FTCs. These results show that freezing and thawing of boreal soils does not have a strong effect on microbial biomass or community structure.     

施肥方式对紫色土农田生态系统N2O和NO排放的影响

依托紫色土施肥方式与养分循环长期试验平台(2002年—),采用静态箱-气相色谱法开展紫色土冬小麦-夏玉米轮作周期(2013年10月至2014年10月)农田生态系统N_2O和NO排放的野外原位观测试验。长期施肥方式包括单施氮肥(N)、传统猪厩肥(OM)、常规氮磷钾肥(NPK)、猪厩肥配施氮磷钾肥(OMNPK)和秸秆还田配施氮磷钾肥(RSDNPK)等5种,氮肥用量相同[小麦季130 kg(N)×hm~(-2),玉米季150 kg(N)×hm~(-2)],不施肥对照(CK)用于计算排放系数,对比不同施肥方式对紫色土典型农田生态系统土壤N_2O和NO排放的影响,以期探寻紫色土农田生态系统N_2O和NO协同减排的施肥方式。结果表明,所有施肥方式下紫色土N_2O和NO排放速率波动幅度大,且均在施肥初期出现峰值;强降雨激发N_2O排放,但对NO排放无明显影响。在整个小麦-玉米轮作周期,N、OM、NPK、OMNPK和RSDNPK处理的N_2O年累积排放量分别为1.40 kg(N)×hm~(-2)、4.60 kg(N)×hm~(-2)、0.95 kg(N)×hm~(-2)、2.16kg(N)×hm~(-2)和1.41 kg(N)×hm~(-2),排放系数分别为0.41%、1.56%、0.25%、0.69%、0.42%;NO累积排放量分别为0.57 kg(N)×hm~(-2)、0.40 kg(N)×hm~(-2)、0.39 kg(N)×hm~(-2)、0.46 kg(N)×hm~(-2)和0.17 kg(N)×hm~(-2),排放系数分别为0.21%、0.15%、0.15%、0.17%、0.07%。施肥方式对紫色土N_2O和NO累积排放量具有显著影响(P0.05),与NPK处理比较,OM和OMNPK处理的N_2O排放分别增加384%和127%,同时NO排放分别增加3%和18%;RSDNPK处理的NO排放减少56%。表明长期施用猪厩肥显著增加N_2O和NO排放,而秸秆还田有效减少NO排放。研究表明,土壤温度和水分条件均显著影响小麦季N_2O和NO排放(P0.01),对玉米季N_2O和NO排放没有显著影响(P0.05),土壤无机氮含量则是在小麦-玉米轮作期N_2O和NO排放的主要限制因子(P0.01)。全量秸秆还田与化肥配合施用是紫色土农田生态系统N_2O和NO协同减排的优化施肥方式。     

The effect of reduced tillage on nitrous oxide emissions of silt loam soils

The effect of reduced tillage (RT) on nitrous oxide (N₂O) emissions of soils from fields with root crops under a temperate climate was studied. Three silt loam fields under RT agriculture were compared with their respective conventional tillage (CT) field with comparable crop rotation and manure application. Undisturbed soil samples taken in September 2005 and February 2006 were incubated under laboratory conditions for 10 days. The N₂O emission of soils taken in September 2005 varied from 50 to 1,095 μg N kg⁻¹ dry soil. The N₂O emissions of soils from the RT fields taken in September 2005 were statistically (P < 0.05) higher or comparable than the N₂O emissions from their respective CT soil. The N₂O emission of soils taken in February 2006 varied from 0 to 233 μg N kg⁻¹ dry soil. The N₂O emissions of soils from the RT fields taken in February 2006 tended to be higher than the N₂O emissions from their respective CT soil. A positive and significant Pearson correlation of the N₂O–N emissions with nitrate nitrogen (NO₃ ⁻–N) content in the soil was found (P < 0.01). Leaving the straw on the field, a typical feature of RT, decreased NO₃ ⁻–N content of the soil and reduced N₂O emissions from RT soils.     

施肥对夏玉米季紫色土N2O排放及反硝化作用的影响

采用原状土柱-乙炔抑制培养法研究了施肥对紫色土玉米生长季土壤N2O排放通量和反硝化作用的影响.结果表明:玉米季施肥显著增加土壤N2O排放和反硝化损失,同时,各施肥处理间N2O排放与反硝化损失量差异显著.猪厩肥、猪厩肥配施氮磷钾肥、氮肥、氮磷钾肥和秸秆配施氮磷钾肥等处理的土壤N,O排放量分别为3.01、2.86、2.51、2.19和1.88 kg hm-2,分别占当季氮肥施用量的1.63％、1.53％、1.30％、1.09％和0.88％,反硝化损失量分别为6.74、6.11、5.23、4.69和4.12 kg hm-2,分别占当季氮肥施用量的3.97％、3.55％、2.97％、2.61％和2.23％,不施肥土壤的N2O排放量和反硝化损失量仅为0.56和0.78 kg hm-2.施肥是紫色土玉米生长前期(2周内)土壤N2O排放和反硝化速率出现高峰的主要驱动因子,土壤铵态氮和硝态氮含量是影响土壤N2O排放、土壤硝化和反硝化作用的限制因子,土壤含水量是重要影响因子,降雨是主要促发因素.土壤N2O排放量与反硝化损失量的比值介于0.45 ～0.72之间,土壤反硝化损失量极显著高于土壤N2O排放量,说明土壤反硝化作用是紫色土玉米生长季氮肥损失的重要途径.     

Decreased nitrous oxide emissions associated with functional microbial genes under bio-organic fertilizer application in vegetable fields

Bio-organic fertilizers enriched with plant growth-promoting microbes(PGPMs)have been widely used in crop fields to promote plant growth and maintain soil microbiome functions.However,their potential effects on N₂O emissions are of increasing concern.In this study,an in situ measurement experiment was conducted to investigate the effect of organic fertilizer containing Trichoderma guizhouense(a plant growth-promoting fungus)on soil N₂O emissions from a greenhouse vegetable field.The following four treatments were used:no fertilizer(control),chemical fertilizer(NPK),organic fertilizer derived from cattle manure(O),and organic fertilizer containing T.guizhouense(O+T,referring to bio-organic fertilizer).The abundances of soil N cycling-related functional genes(amoA)from ammonium-oxidizing bacteria(AOB)and archaea(AOA),as well as nirS,nirK,and nosZ,were simultaneously determined using quantitative PCR(qPCR).Compared to the NPK plot,seasonal total N₂O emissions decreased by 11.7%and 18.7%in the O and O+T plots,respectively,which was attributed to lower NH₄⁺-N content and AOB amoA abundance in the O and O+T plots.The nosZ abundance was significantly greater in the O+T plot,whilst the AOB amoA abundance was significantly lower in the O+T plot than in the O plot.Relative to the organic fertilizer,bio-organic fertilizer application tended to decrease N₂O emissions by 7.9%and enhanced vegetable yield,resulting in a significant decrease in yield-scaled N₂O emissions.Overall,the results of this study suggested that,compared to organic and chemical fertilizers,bio-organic fertilizers containing PGPMs could benefit crop yield and mitigate N₂O emissions in vegetable fields.     

微生物介导的农业土壤氧化亚氮减排研究进展

氧化亚氮(N₂O)是一种在大气存留时间长且破坏臭氧层的重要温室气体。农业土壤源N₂O是其重要来源,具有产生路径广、影响因素多、调控复杂等特点。减少农业土壤N₂O排放一直是研究的热点。含有N₂O还原酶的N₂O还原细菌能将N₂O还原为氮气(N2),这是目前已知的微生物还原N₂O唯一的汇。直接应用微生物减少农业土壤N₂O排放是一种新兴的减排技术。本文详细阐述了农业土壤N₂O的生物源与汇,重点论述了N₂O减排微生物的筛选及应用策略。综述了微生物介导的农业土壤N₂O减排的两种微生物生态学机制：一种是利用含有nos Z基因的N₂O还原细菌直接减少N₂O排放,另一种是利用能改变N₂O还原细菌群落组成和丰度及其活性的植物根际促生菌间接减少N₂O排放。最后,讨论了影响微生物介导的...     

不同耕作措施对雨养冬小麦碳足迹的影响

为了解不同耕作管理措施对我国北方旱作农田作物生产生命周期内生产资料及生产过程碳排放足迹的影响,在山西省临汾市尧都区连续15年保护性耕作长期定位试验基地,利用静态箱-气相色谱法连续两年测定了不同秸秆管理和耕作措施(秸秆不还田旋耕、秸秆还田旋耕、秸秆覆盖免耕)下,旱作冬小麦田N_2O周年排放通量,并对不同耕作管理措施的生产资料和生产过程中的碳排放进行全面分析与计算,以估算不同耕作措施的碳足迹。结果表明:1)秸秆覆盖免耕和秸秆不还田旋耕条件下旱作冬小麦田N_2O年度累积排放量较秸秆还田旋耕分别平均减少19.2%和18.9%;2)旱作冬小麦在秸秆覆盖免耕条件下产量最高;3)旱作农田碳足迹中氮肥生产、农田N_2O直接排放和柴油消耗排放占到总排放足迹的90%以上;4)秸秆覆盖免耕较其他耕作方式的碳足迹低,两年试验期间,较秸秆还田旋耕处理碳足迹分别低11.0%和6.9%,较秸秆不还田旋耕处理碳足迹分别低7.9%和8.3%。5)在半干旱地区,秸秆覆盖免耕处理单位产量碳足迹最低,是本研究中低碳低排的推荐措施。本研究结果可为旱作农田以低碳减排为目标的可持续发展提供科学依据。     

NH3 Volatilization,N2O Emission and Microbial Biomass Turnover from 15N-Labeled Manure Under Laboratory Conditions

On irrigated agricultural soils from semi-arid and arid regions, ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission can be a considerable source of N losses. This study was designed to test the capture of ¹⁵N loss as NH₃ and N₂O from previous and recent manure application using a sandy, calcareous soil from Oman amended one or two times with ¹⁵N labeled manure to elucidate microbial turnover processes under laboratory conditions. The system allowed to detect ¹⁵N enrichments in evolved N₂O-N and NH₃-N of up to 17% and 9%, respectively, and total N, K₂SO₄ extractable N and microbial N pools from previous and recent ¹⁵N labeled manure applications of up to 7%, 8%, and 15%. One time manured soil had higher cumulative N₂O-N emissions (141 µg kg^?1) than repeatedly manured soil with 43 µg kg^?1 of which only 22% derived from recent manure application indicating a priming effect.     

Dinitrogen emissions and the N2:N2O emission ratio of a Rendzic Leptosol as influenced by pH and forest thinning

Reduction of nitrous oxide (N₂O) to dinitrogen (N₂) by denitrification in soils is of outstanding ecological significance since it is the prevailing natural process converting reactive nitrogen back into inert molecular dinitrogen. Furthermore, the extent to which N₂O is reduced to N₂ via denitrification is a major regulating factor affecting the magnitude of N₂O emission from soils. However, due to methodological problems in the past, extremely little information is available on N₂ emission and the N₂:N₂O emission ratio for soils of terrestrial ecosystems. In this study, we simultaneously determined N₂ and N₂O emissions from intact soil cores taken from a mountainous beech forest ecosystem. The soil cores were taken from plots with distinct differences in microclimate (warm-dry versus cool-moist) and silvicultural treatment (untreated control versus heavy thinning). Due to different microclimates, the plots showed pronounced differences in pH values (range: 6.3–7.3). N₂O emission from the soil cores was generally very low (2.0 ± 0.5–6.3 ± 3.8 μg N m⁻² h⁻¹ at the warm-dry site and 7.1 ± 3.1–57.4 ± 28.5 μg N m⁻² h⁻¹ at the cool-moist site), thus confirming results from field measurements. However, N₂ emission exceeded N₂O emission by a factor of 21 ± 6–220 ± 122 at the investigated plots. This illustrates that the dominant end product of denitrification at our plots and under the given environmental conditions is N₂ rather than N₂O. N₂ emission showed a huge variability (range: 161 ± 64–1070 ± 499 μg N m⁻² h⁻¹), so that potential effects of microclimate or silvicultural treatment on N₂ emission could not be identified with certainty. However, there was a significant effect of microclimate on the magnitude of N₂O emission as well as on the mean N₂:N₂O emission ratio. N₂:N₂O emission ratios were higher and N₂O emissions were lower for soil cores taken from the plots with warm-dry microclimate as compared to soil cores taken from the cool-moist microclimate plots. We hypothesize that the increase in the N₂:N₂O emission ratio at the warm-dry site was due to higher N₂O reductase activity provoked by the higher soil pH value of this site. Overall, the results of this study show that the N₂:N₂O emission ratio is crucial for understanding the regulation of N₂O fluxes of the investigated soil and that reliable estimates of N₂ emissions are an indispensable prerequisite for accurately calculating total N gas budgets for the investigated ecosystem and very likely for many other terrestrial upland ecosystems as well.     

Fluxes and production pathways of nitrous oxide in different types of tropical forest soils in Thailand

Nitrous oxide (N₂O) emissions from the soil surface of five different forest types in Thailand were measured using the closed chamber method. Soil samples were also taken to study the N₂O production pathways. The monthly average emissions (±SD, n?=?12) of N₂O from dry evergreen forest (DEF), hill evergreen forest (HEF), moist evergreen forest (MEF), mixed deciduous forest (MDF) and acacia reforestation (ARF) were 13.0?±?8.2, 5.7?±?7.1, 1.2?±?12.1, 7.3?±?8.5 and 16.7?±?9.2?µg N m^?2 h^?1, respectively. Large seasonal variations in fluxes were observed. Emission was relatively higher during the wet season than during the dry season, indicating that soil moisture and denitrification were probably the main controlling factors. Net N₂O uptake was also observed occasionally. Laboratory studies were conducted to further investigate the influence of moisture and the N₂O production pathways. Production rates at 30% water holding capacity (WHC) were 3.9?±?0.2, 0.5?±?0.06 and 0.87?±?0.01?ng N₂O-nitrogen (N) g-dw^?1day^?1 in DEF, HEF and MEF respectively. At 60% WHC, N₂O production rates in DEF, HEF and MEF soils increased by factors of 68, 9 and 502, respectively. Denitrification was found to be the main N₂O production pathway in these soils except in MEF.     

施肥方式对冬小麦季紫色土N2O排放特征的影响

利用紫色土养分循环长期定位施肥试验平台,通过静态箱-气相色谱法,于2012年11月至2013年5月,研究了单施氮肥(N)、猪厩肥(OM)、常规氮磷钾肥(NPK)、猪厩肥配施氮磷钾肥(OMNPK)、秸秆还田配施氮磷钾肥(CRNPK)及对照不施肥(NF)6种施肥方式下,紫色土冬小麦季土壤N2O的排放特征。结果表明,在相同施氮水平[130 kg(N)·hm-2]下,施肥方式对N2O排放量有显著影响(P0.05)。N、OM、NPK、OMNPK和CRNPK处理下,土壤N2O排放量[kg(N)·hm-2]分别为0.38、0.36、0.29、0.33和0.19,N2O排放系数分别为0.25%、0.23%、0.18%、0.21%和0.10%。NF的土壤N2O排放量为0.06 kg(N)·hm-2。土壤无机氮含量(NO3--N和NH4+-N)是N2O排放的主要影响因子,降雨能有效激发N2O排放。基于小麦产量评价不同施肥方式下的N2O排放,结果表明,N、OM、NPK、OMNPK和CRNPK单位小麦产量N2O的GWP值[yield-scaled GWP,kg(CO2 eq)·t-1]分别为132.57、45.70、49.07、48.92和26.41。CRNPK的小麦产量与6种施肥方式中获得最大产量的OM间没有显著差异,但显著高于其他处理。而且,CRNPK的yield-scaled GWP比紫色土地区冬小麦种植中常规施肥方式(NPK)显著减少46%,并显著低于其他4种施肥方式。可见,秸秆还田配施氮磷钾肥在保证小麦产量的同时,能有效减少因施肥引发的N2O排放,可作为紫色土地区推荐的最佳施肥措施。     

Linkage of N2O emissions to the abundance of soil ammonia oxidizers and denitrifiers in purple soil under long-term fertilization

Abstract

Microbial nitrification and denitrification are responsible for the majority of soil nitrous (N₂O) emissions. In this study, N₂O emissions were measured and the abundance of ammonium oxidizers and denitrifiers were quantified in purple soil in a long-term fertilization experiment to explore their relationships. The average N₂O fluxes and abundance of the amoAgene in ammonia-oxidizing bacteria during the observed dry season were highest when treated with mixed nitrogen, phosphorus and potassium fertilizer (NPK) and a single N treatment (N) using NH₄HCO₃as the sole N source; lower values were obtained using organic manure with pig slurry and added NPK at a ratio of 40%:60% (OMNPK),organic manure with pig slurry (OM) and returning crop straw residue plus synthetic NH₄HCO₃fertilizer at a ratio of 15%:85% (SRNPK). The lowest N₂O fluxes were observed in the treatment that used crop straw residue(SR) and in the control with no fertilizer (CK). Soil NH₄⁺provides the substrate for nitrification generating N₂O as a byproduct. The N₂O flux was significantly correlated with the abundance of the amoA gene in ammonia-oxidizing bacteria (r = 0.984, p < 0.001), which was the main driver of nitrification. During the wet season, soil nitrate (NO₃^?) and soil organic matter (SOC) were found positively correlated with N₂O emissions (r = 0.774, p = 0.041 and r = 0.827, p = 0.015, respectively). The nirS gene showed a similar trend with N₂O fluxes. These results show the relationship between the abundance of soil microbes and N₂O emissions and suggest that N₂O emissions during the dry season were due to nitrification, whereas in wet season, denitrification might dominate N₂O emission.     

Nitrous oxide emissions from agricultural soils at low temperatures: a laboratory microcosm study

We studied in laboratory microcosms (intact soil cores) N₂O and CO₂ emissions from four different agricultural soil types (organic soil, clay, silt and loam) at low temperatures with or without freezing-thawing events. When the temperature of the frozen soil cores was increased stepwise from −8 °C the N₂O emissions began to increase at −0.5 °C, and peaked at −0.1 °C in the organic, clay and silt soils, and at +1.6 °C in the loam soils. However, a stepwise decrease in soil temperature from +15 °C also induced an increase in the N₂O emissions close to the 0 °C. These emissions peaked between −0.4 and +2.5 °C depending on the soil type and water content. However, the emission maxima were from 2 to 14.3% of those encountered in the experiments where frozen soils were thawed. Our results show that in addition to the well-documented thawing peak, soils also can have a maximum in their N₂O emission near 0 °C when soil temperature decrease. These emissions, however, are less than those emitted from thawing soils. The correlations between the N₂O and CO₂ emissions were weak. Our results suggest that N₂O is produced in soils down to a temperature of −6 °C.     

Effects of nitrogen fertilization and irrigation on N2O emissions from a sandy soil in Germany

The aim of this study was to investigate the effect of supplemental irrigation on the amount of N₂O emissions on a sandy soil in north-east Germany. N₂O flux measurements were carried out over two vegetation periods from the emergence of plants to harvest. The level of N₂O emissions was low, which is typical for sandy soils in north-east Germany. In both periods, irrigation had no increasing effect on N₂O emissions. Relevant factors were the soil temperature and the soil water-filled pore space (WFPS), which were mainly influenced by weather conditions. This may indicate that nitrification was the main source of N₂O emissions. In conclusion, this study has confirmed that sandy soils under weather conditions of north-east Germany generally have a very low potential for N₂O emissions.     

Effects of land-use type and nitrogen addition on nitrous oxide and carbon dioxide production potentials in Japanese Andosols

Land-use type and nitrogen (N) addition strongly affect nitrous oxide (N₂O) and carbon dioxide (CO₂) production, but the impacts of their interaction and the controlling factors remain unclear. The aim of this study was to evaluate the effect of both factors simultaneously on N₂O and CO₂ production and associated soil chemical and biological properties. Surface soils (0–10 cm) from three adjacent lands (apple orchard, grassland and deciduous forest) in central Japan were selected and incubated aerobically for 12 weeks with addition of 0, 30 or 150 kg N ha^–1 yr^–1. Land-use type had a significant (p < 0.001) impact on the cumulative N₂O and CO₂ production. Soils from the apple orchard had higher N₂O and CO₂ production potentials than those from the grassland and forest soils. Soil net N mineralization rate had a positive correlation with both soil N₂O and CO₂ production rates. Furthermore, the N₂O production rate was positively correlated with the CO₂ production rate. In the soils with no N addition, the dominant soil properties influencing N₂O production were found to be the ammonium-N content and the ratio of soil microbial biomass carbon to nitrogen (MBC/MBN), while those for CO₂ production were the content of nitrate-N and soluble organic carbon. N₂O production increased with the increase in added N doses for the three land-use types and depended on the status of the initial soil available N. The effect of N addition on CO₂ production varied with land use type; with the increase of N addition doses, it decreased for the apple orchard and forest soils but increased for the grassland soils. This difference might be due to the differences in microbial flora as indicated by the MBC/MBN ratio. Soil N mineralization was the major process controlling N₂O and CO₂ production in the examined soils under aerobic incubation conditions.