不同土地利用方式下土壤温度与土壤水分对黑土N2O排放的影响

采用静态箱一气象色谱法,对黑土区3种不同土地利用方式（草地、裸地和农田）下土壤氧化亚氮（N：O）的排放特征及其与土壤温度和土壤水分的关系进行研究。结果显示：试验监测期间（2011年5月27日-9月30日）,不同土地利用方式下,土壤N：0累积排放量分别为草地52．08mgN·m^-2裸地64．43mgN·m^-2农田70．16mgN·m^-2,农田土壤N：O累积排放量比草地和裸地分别高出35％和9％,草地、裸地和农田的N2O平均排放通量分别为16．56、20．36、21．44μgN·m^-2·h^-1。草地和裸地中,土壤N2O排放通量与土壤温度和土壤水分（充水孔隙度,WFPS）相关性均不显著,但在农田中,土壤N20排放通量与土壤温度（5cm和10cm）和土壤水分（5cm）均呈显著正相关（P〈0．05）。另外,土壤N2O累积排放量与土壤硝态氮和矿质氮含量均呈正相关关系。研究表明,黑土草地开垦可促进土壤N2O的排放,且不同土地利用方式下土壤N2O排放的主要影响因子不同。     

Fluxes of nitrous oxide and nitric oxide from experimental excreta patches in boreal agricultural soil

Nitric oxide (NO) and nitrous oxide (N₂O) emissions were measured from experimental dung and urine patches placed on boreal pasture soil during two growing seasons and one autumn period until soil freezing. N₂O emissions in situ were studied by a static chamber method. NO was measured with a dynamic chamber method using a NO analyser in situ. Mean emissions from the control plots were 47.6±4.5 μg N₂ON m⁻² h⁻¹ and 12.6±1.6 μg NON m⁻² h⁻¹. N₂O and NO emissions from urine plots (132±21.2 μg N₂ON m⁻² h⁻¹ and 51.9±7.6 μg NON m⁻² h⁻¹) were higher than those from dung plots (110.0±20.1 μg N₂ON m⁻² h⁻¹ and 14.7±2.1 μg NON m⁻² h⁻¹). There was a large temporal variation in N₂O and NO emissions. Maximum N₂O emissions were measured a few weeks after dung or urine application, whereas the maximum NO emissions were detected the following year. NO was responsible on average 14% (autumn) and 34% (summer) of total (NO+N₂O)N emissions from the pasture soil. NO emissions increased with increasing soil temperature and with decreasing soil moisture. N₂O emissions increased with increasing soil moisture, but did not correlate with soil temperature. Therefore we propose that N₂O and NO were produced mainly during different microbial processes, i.e., nitrification and denitrification, respectively. The results show that the overall conditions and mechanism especially for emissions of NO are still poorly understood but that there are differences in the mechanisms regulating N₂O and NO production.     

Dinitrogen and N2O emissions in arable soils: Effect of tillage, N source and soil moisture

A laboratory investigation was performed to compare the fluxes of dinitrogen (N₂), N₂O and carbon dioxide (CO₂) from no-till (NT) and conventional till (CT) soils under the same water, mineral nitrogen and temperature status. Intact soil cores (0-10 cm) were incubated for 2 weeks at 25 °C at either 75% or 60% water-filled pore space (WFPS) with ¹⁵N-labeled fertilizers (100 mg N kg⁻¹ soil). Gas and soil samples were collected at 1-4 day intervals during the incubation period. The N₂O and CO₂ fluxes were measured by a gas chromatography (GC) system while total N₂ and N₂O losses and their ¹⁵N mole fractions in the soil mineral N pool were determined by a mass spectrometer. The daily accumulative fluxes of N₂ and N₂O were significantly affected by tillage, N source and soil moisture. We observed higher (P<0.05) fluxes of N₂+N₂O, N₂O and CO₂ from the NT soils than from the CT soils. Compared with the addition of nitrate (NO₃⁻), the addition of ammonium (NH₄⁺) enhanced the emissions of these N and C gases in the CT and NT soils, but the effect of NH₄⁺ on the N₂ and/or N₂O fluxes was evident only at 60% WFPS, indicating that nitrification and subsequent denitrification contributed largely to the gaseous N losses and N₂O emission under the lower moisture condition. Total and fertilizer-induced emissions of N₂ and/or N₂O were higher (P<0.05) at 75% WFPS than with 60% WFPS, while CO₂ fluxes were not influenced by the two moisture levels. These laboratory results indicate that there is greater potential for N₂O loss from NT soils than CT soils. Avoiding wet soil conditions (>60% WFPS) and applying a NO₃⁻ form of N fertilizer would reduce potential N₂O emissions from arable soils.     

CO2 emission in an intensively cultivated loam as affected by long-term application of organic manure and nitrogen fertilizer

A long-term field experiment was conducted to examine the influence of mineral fertilizer and organic manure on the equilibrium dynamics of soil organic C in an intensively cultivated fluvo-aquic soil in the Fengqiu State Key Agro-Ecological Experimental Station (Fengqiu county, Henan province, China) since September 1989. Soil CO₂ flux was measured during the maize and wheat growing seasons in 2002-2003 and 2004 to evaluate the response of soil respiration to additions and/or alterations in mineral fertilizer, organic manure and various environmental factors. The study included seven treatments: organic manure (OM), half-organic manure plus half-fertilizer N (NOM), fertilizer NPK (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer PK (PK) and control (CK). Organic C in soil and the soil heavy fraction (organo-mineral complex) was increased from 4.47 to 8.61 mg C g⁻¹ and from 3.32 to 5.68 mg C g⁻¹, respectively, after the 13 yr application of organic manure. In contrast, organic C and the soil heavy fraction increased in NPK soil to only 5.41 and 4.38 mg C g⁻¹, respectively. In the CK treatment, these parameters actually decreased from the initial C concentrations (4.47 and 3.32 mg C g⁻¹) to 3.77 and 3.11 mg C g⁻¹, respectively. Therefore, organic manure efficiently elevated soil organic C. However, only 66% of the increased soil organic C was combined with clay minerals in the OM treatment. Cumulative soil CO₂ emissions from inter-row soil in the OM and NPK treatments were 228 and 188 g C m⁻² during the 2002 maize growing season, 132 and 123 g C m⁻² during the 2002/2003 wheat growing season, and 401 and 346 g C m⁻² yr⁻¹ in 2002-2003, respectively. However, during the 2004 maize growing season, cumulative soil CO₂ emissions were as high as 617 and 556 g C m⁻², respectively, due to the contribution of rhizosphere respiration. The addition of organic manure contributed to a 16% increase in soil CO₂ emission in 2002-2003 (compared to NPK), where only 27%, 36% and 24% of applied organic C was released as CO₂ during the 2002 and 2004 maize growing seasons and in 2002-2003, respectively. During the 2002/2003 wheat growing season, soil CO₂ flux was significantly affected by soil temperature below 20 °C, but by soil moisture (WFPS) during the 2004 maize growing season at soil temperatures above 18 °C. Optimum soil WFPS for soil CO₂ flux was approximately 70%. When WFPS was below 50%, it no longer had a significant impact on soil CO₂ flux during the 2002 maize growing season. This study indicates the application of organic manure composted with wheat straw may be a preferred strategy for increasing soil organic C and sequestering C in soil.     

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.     

Effects of water content and N addition on potential greenhouse gas production from two differently textured soils under laboratory conditions

GHGs production and emission may vary depending on soil physical properties, water management and fertilization. Two paddy soils characterized by different texture were incubated to evaluate the impact of flooding (permanent or intermittent) and N addition on potential N₂O, CH₄ and CO₂ production and release into atmosphere and soil solution. Relationships with volumetric water content (VWC) and water filled pore space (WFPS) were evaluated. Overall, the finer clayey soil (CL) produced 58% more CH₄ than the coarser sandy soil (SA) and showed an earlier sink to source transition; the difference was lower with N addition. Permanent flooding favoured the amount of dissolved CH₄. SA produced more N₂O emissions than CL under permanent flooding (31.0 vs. 3.7%); an opposite pattern was observed for dissolved N₂O (16.4 vs. 52.7%). Fertilization increased N₂O emissions under dry conditions in CL and under flooding in SA.

Our findings showed that i) VWC had a larger influence on N₂O and CH₄ emissions than WFPS, ii) soil type influenced the gas release into atmosphere or soil solution and the timing of sink to source transition in CH₄ emissions. Further investigation on timing of fertilization and drainage are needed to improve climate change mitigation strategies.     

土壤含水量对硝化和反硝化过程N_2O排放及同位素特征值的影响

【目的】通过室内培养试验,研究不同含水量对北京顺义潮褐土N_2O排放及同位素特征值(δ15Nbulk,δ18O和nitrogen isotopomer site preference of N_2O,简称SP)的影响,以期获得不同水分条件下土壤N_2O产生途径及变化规律,为农田土壤N_2O减排提供理论依据。【方法】结合稳定同位素技术与乙炔抑制法,以北京顺义潮褐土为试材,设置3个含水量梯度:67%、80%和95%WFPS(土壤体积含水量与总孔隙度的百分比或实际重量含水量与饱和含水量的百分比,简称WFPS),在此基础上设置无C2H2,0.1%(V/V)C2H2和10%(V/V)C2H2处理。将土壤装入培养瓶中培养2 h,之后收集培养瓶中的气体测定N_2O浓度及同位素特征值,并采集土样测定其NH+4-N和NO-3-N的含量。利用同位素二源混合模型计算硝化和反硝化作用对土壤N_2O排放的贡献率,对N_2O产生途径进行量化分析。【结果】根据室内土壤培养测定结果,高(95%WFPS)、中(80%WFPS)和低(67%WFPS)含水量土壤N_2O加权平均排放通量分别为1.17、0.27和0.08 mg N·kg-1·d-1,高含水量土壤N_2O排放量均显著高于中、低含水量处理,中含水量处理显著高于低含水量;整个培养周期,高、中和低含水量土壤N_2O+N_2累积排放量分别为培养初期总的无机氮含量的18.05%、5.27%和1.24%(N_2O+N_2累积排放量分别为19.61、5.72和1.35 mg N·kg-1;各处理NH+4-N+NO-3-N初始含量均为108.62 mg N·kg-1);与低含水量处理相比,高、中含水量土壤的N_2O+N_2累积排放量分别增加了13.53倍和3.24倍,高含水量土壤N_2O+N_2累积排放量比中含水量高2.43倍,表现为随着含水量的增加,土壤无机氮(NH+4-N+NO-3-N)以气态氮(N_2O+N_2)形式的损失量逐渐增加。3个含水量处理N_2O的δ15Nbulk加权平均值变化范围为-42.93‰—-4.07‰,且较高含水量处理显著低于较低含水量处理;10%(V/V)C2H2抑制土壤中N_2O还原成N_2的过程,各含水量土壤中,10%(V/V)C2H2处理组其N_2O的δ18O值显著低于0.1%(V/V)C2H2处理组,且N_2O/(N_2O+N_2)比率随土壤含水量增加而降低;各处理土壤中同时存在多个N_2O产生过程,对于培养第一周,土壤产生的N_2O的SP值于培养前4 d呈逐渐增加的趋势,之后又逐渐降低,低含水量土壤在第1—2天产生的N_2O的SP值为6.74‰—12.04‰,反硝化作用对土壤N_2O排放的贡献率为56.36%—66.15%,此培养阶段表现为土壤主要通过反硝化作用产生N_2O,之后,硝化作用贡献率(55.78%—100%)增强;中含水量土壤N_2O的SP加权平均值为10.26‰,该土壤中反硝化作用(40.90%—74.04%)占据主导地位;加10%(V/V)C2H2的高含水量处理,在整个培养第一周均具有较高的SP值,变化范围为7.61‰—21.11‰;与0.1%(V/V)C2H2处理组相比,10%(V/V)C2H2处理的高、中和低含水量土壤排放N_2O的SP加权平均值分别降低了0.10倍、0.33倍和0.06倍。【结论】土壤含水量增加促进N_2O排放,高含水量处理中N_2O排放量最高。67%WFPS处理中,N_2O排放前期以反硝化作用为主,后期以硝化作用为主;80%WFPS处理中,N_2O主要由反硝化过程产生;95%WFPS处理中,N_2O排放以硝化作用为主。     

旱地反硝化作用和N2O排放影响因子的研究

用乙炔抑制原状土柱和模拟土柱法,研究了包括水分、碳源、氮源以及反硝化的主要决定因子水分干湿交替对土壤N2O排放量的影响。结果表明,影响旱地土壤反硝化的主要因子是作为微生物能源和碳源的有机物质,在碳源充足时,土壤的硝态氮含量和水分因子是限制因子;两种氮源相比较,在一定的碳含量和水分条件下,土壤N2O排放量并不随NO3--N加入量的增加而增大,最大N2O排放量发生在氮源加入量为300 mg/kg时;而当氮源为NO2--N时,土壤N2O排放量随NO2--N加入量的增加而增大,最大排放量为NO2--N为450 mg/kg处理。在同等土壤水分条件下,土壤由湿变干过程中产生的N2O通量高于土壤由干变湿过程中的产生量;土壤由干变湿过程中N2O通量随着土壤水充孔隙空间(WFPS)含量的增加而增大,但在土壤由湿变干过程中最大N2O通量并非在土壤水分饱和状态下,而是在土壤WFPS为70%时,而后N2O排放量随土壤WFPS含量的减少而降低;施肥处理土壤与不施肥对照相比,两者的N2O通量变化趋势相同,但对照的变化幅度相对较小。     

The utility of process-based models for simulating N2O emissions from soils: A case study based on Costa Rican coffee plantations

Soil moisture and gaseous N-flux (N₂O, N₂) dynamics in Costa Rican coffee plantations were successively simulated using a mechanistic model (PASTIS) and two process-based models (NGAS and NOE). Two fertilized (250 kg N ha⁻¹ y⁻¹) coffee plantations were considered, namely a monoculture and a system shaded by the N₂ fixing legume species Inga densiflora. In situ N₂O fluxes were previously measured in these plantations. NGAS and NOE used specific microbial activities for the soils. To parameterize NGAS, we estimated N mineralization via in situ incubations and the contribution of heterotrophic soil respiration to total soil respiration. Potential denitrification rates and the proportion of denitrified N emitted as N₂O were measured in the laboratory to define the values of NOE parameters, as well as nitrification rates and related N₂O production rates for parameterizing both models. Soil moisture and both NGAS and NOE N₂O fluxes were best modelled on an hourly time step. Soil moisture dynamics were satisfactorily simulated by PASTIS. Simulated N₂O fluxes by both NGAS and NOE (3.2 and 2.1 kg N ha⁻¹ y⁻¹ for NGAS; 7.1 and 3.7 kg N ha⁻¹ y⁻¹ for NOE, for the monoculture and shaded plantations respectively) were within a factor of about 2 of the observed annual fluxes (4.3 and 5.8 kg N ha⁻¹ y⁻¹, for the monoculture and shaded plantations respectively). Statistical indicators of association and coincidence between simulated and measured values were satisfactory for both models. Nevertheless, the two models differed greatly in describing the nitrification and denitrification processes. Some of the algorithms in the model NGAS were apparently not applicable to these tropical acidic Andosols. Therefore, more detailed information about microbial processes in different agroecosystems would be needed, notably if process-oriented models were to be used for testing strategies for mitigating N₂O emissions.     

灌溉和降水对旱地土壤N2O气态损失的影响

利用土壤探头法和密闭气室法相结合 ,就黄土高原旱地土壤玉米生长期灌溉和降水对N2O气态损失的影响进行了研究 ;并采用乙炔抑制原状土柱培养法 ,对土壤由湿变干和由干变湿过程中N2O变化进行了模拟。试验结果表明 ,在旱地土壤上 ,N2O的变化一般较小 ,但在降雨或者灌溉后无论是土壤N2O通量或者土壤剖面中N2O的浓度均呈现上升趋势 ,且这种变化趋势与同时期降雨量的变化趋势相同。培养结果说明 ,在相同的土壤孔隙水含量 (WFPS)条件下 ,土壤由湿变干过程产生的N2O通量高于土壤由干变湿过程中的产生量 ;在土壤由干变湿过程中N2O通量随土壤WFPS含量的增加而上升 ,但在土壤由湿变干过程中土壤N2O通量在WFPS含量为 70%时达到最大 ,而后随土壤WFPS含量的减少而下降。施肥处理与对照相比两者的变化趋势相同 ,但不施肥处理的变化幅度较小