New method for the estimation of nitrous oxide emission rates from an agricultural watershed

Abstract

We developed a new and improved method, the ‘high-emission-incorporation (HEI) method’, for estimating soil nitrous oxide (N₂O) emission rates at a watershed level based on nitrogen (N) input (consisting of fertilizer, manure, slurry and excreta N) and N surplus (calculated by subtracting the amount of crop yield and consumed N from the N input) of different sites in a livestock farm located in a watershed. The main characteristic of this method is the inclusion of extremely high N₂O emission rates, ‘outlier’, which are normally excluded from estimation. High N₂O emission rates were estimated using the regression model obtained from the measured N₂O values and the amounts of N surplus; normal N₂O emission rates were estimated using the regression model obtained from the measured values and the amount of N input. The probability of occurrence of a high flux was used to incorporate calculated high and normal N₂O emissions into one. The annual N₂O emission rate from the livestock farm in the watershed (467?ha), estimated using the HEI method, was 1156?±?147?kg?N?year^?1 over a 5-year period. The annual N₂O emission rates calculated using the site-specific emission factor (EF?=?0.0789) and the emission factor of the Intergovernmental Panel on Climate Change (EF?=?0.01) were 1838?±?585?kg?N?year^?1 and 673 (522–1103) kg?N?year^?1, respectively. The estimated value using the measure-and-multiply method, in which each land-use area is multiplied by the representative emission rate for each land-use type, was 964 (509–1610) kg?N?year^?1. The N₂O emission rates estimated by our newly developed method were consistent with the values calculated by the measure-and-multiply method and offered improvement over this measure because the new measure can also predict future N₂O emission rates from the watershed.     

妊娠猪舍氨气及氧化亚氮浓度测定与排放通量的估算

在北京选择一典型猪场，对不同季节妊娠舍的氨气及氧化亚氮浓度进行了为期1年的试验测定，并根据二氧化碳平衡原理，对猪场不同生长阶段的妊娠猪含氮气体的排放通量进行了估算。结果表明：冬季2004年11月氨气和氧化亚氮的平均浓度分别为11.64±4.36，（1.17±0.2）mg／m³，夏季7月舍内氨气和氧化亚氮的平均浓度分别为3.31±2.67，（0.6±0.02）mg／m³；妊娠猪饲养期间的氨气排放通量为每头（185.2～500.8）mg／h，氧化亚氮为（3.85～35.93）mg／h。     

应用修正的IPCC2006方法对中国农田N2O排放量重新估算

氧化亚氮(N2O)是一种重要的温室气体,农田土壤是其排放的重要源。本研究通过本地参数修正的IPCC2006计算方法,结合统计资料计算中国农田土壤的N2O直接排放量。结果表明:从1980年到2007年中国农田N2O排放年均增长7.6%,2007年N2O-N排放量达到288.4Gg。2007年化学氮肥投入、有机物质投入、作物秸秆投入、有机土排放对农田N2O直接排放的贡献份额分别为77.64%、15.57%、6.46%和0.33%。从分布格局看,2007年农田N2O直接排放总量较大省份主要集中在华北地区和四川盆地,单位耕地面积N2O排放量较高的地区主要集中在华北地区和东南沿海。     

妊娠猪舍氨气及氧化亚氮浓度测定与排放通量的估算

在北京选择一典型猪场,对不同季节妊娠舍的氨气及氧化亚氮浓度进行了为期1年的试验测定,并根据二氧化碳平衡原理,对猪场不同生长阶段的妊娠猪含氮气体的排放通量进行了估算。结果表明:冬季2004年11月氨气和氧化亚氮的平均浓度分别为(11．64±4．36),(1．17±0．2)mg／m~3,夏季7月舍内氨气和氧化亚氮的平均浓度分别为(3．31±2．67),(0．6±0．02)mg／m~3;妊娠猪饲养期间的氨气排放通量为每头(185．2～500．8)mg／h,氧化亚氮为(3．85～35．93)mg／h。     

Interactive effects of ammonium application rates and temperature on nitrous oxide emission from tropical agricultural soil

Emissions of nitrous oxide (N₂O), a potent greenhouse gas, from agricultural soil have been recognized to be affected by nitrogen (N) application and temperature. Most of the previous studies were carried out to determine effects of temperature on N₂O emissions at a fixed N application rate or those of N application rates at a specific temperature. Knowledge about the effects of different ammonium (NH₄⁺) application rates and temperatures on N₂O emissions from tropical agricultural soil and their interactions is limited. Five grams of air-dried sandy loam soil, collected in Central Vietnam, were adjusted to 0, 400, 800 and 1200 mg NH₄-N kg^–1 soil (abbreviated as 0 N, 400 N, 800 N and 1200 N, respectively) at 60% water holding capacity were aerobically incubated at 20°C, 25°C, 30°C or 35°C for 28 days. Mineral N contents and N₂O emission rates were determined on days 1, 3, 5, 7, 14, 21 and 28. Cumulative N₂O emissions for 28 days increased with increasing NH₄⁺ application rates from 0 to 800 mg N kg^–1 and then declined to 1200 mg N kg^–1. Cumulative N₂O emissions increased in the order of 35°C, 20°C, 30°C and 25°C. This lowest emission at 35°C occurred because N₂O production was derived only from autotrophic nitrification while other N₂O production processes, e.g., nitrifier denitrification and coupled nitrification-denitrification occurred at lower temperatures. More specifically, cumulative N₂O emissions peaked at 800 N and 25°C, and the lowest emissions occurred at 1200 N and 35°C. In conclusion, N₂O emissions were not exponentially correlated with NH₄⁺ application rates or temperatures. Higher NH₄⁺ application rates at higher temperatures suppressed N₂O emissions.     

典型潮土N2O排放的DNDC模型田间验证研究

利用典型潮土N2O排放的田间试验数据对脱氮-分解模型（DNDC）及其参数进行验证。结果表明,DNDC模型能较好地模拟田间实测到的冬小麦、夏玉米季土壤湿度和土壤日平均地表温度的动态变化。小麦和玉米季土壤N2O排放通量与土壤水分（WFPS）呈显著正相关,与土壤温度相关性不大。田间实测到的N2O排放高峰主要受降水和施肥的影响,在N2O排放峰的峰值和出现时间上模拟值与实测值较接近,但准确地捕捉N2O季节性的排放通量仍需对模型进行修正。通过比较施肥、土壤和田间管理等输入参数的改变对DNDC模型进行灵敏性分析,氮肥用量、施肥次数、土壤初始无机氮含量和土壤质地的改变对土壤N2O排放量均很敏感,其中氮肥用量和施肥次数的改变最为敏感。基于当地土壤特性和田间管理的校正,DNDC模型为评价农田生态系统N2O的排放提供了强有力的工具。     

不同施肥处理稻田甲烷和氧化亚氮排放特征

采用静态箱－气相色谱法对长期不同施肥处理(NPKS、CK、NPK和NKM)的稻田CH₄和N₂O排放进行了观测。结果表明,稻田CH₄和N₂O排放季节变化规律明显不同,二者排放通量季节变化呈显著负相关(p<0.01)。与单施化肥和CK相比,施用有机肥显著促进CH₄排放,排放量最高的NPKS处理早晚稻田排放量分别是：526.68 kg/hm²和1072.92 kg/hm²。对于N₂O排放,早稻田各处理间差异不显著,NPK处理排放量最大,为1.48 kg/hm²;晚稻田各处理差异极显著(p<0.01),NPKS处理排放量最大,为1.40 kg/hm²。晚稻田CH₄排放通量和10 cm土层温度及土壤pH值相关极显著(p<0.01),并与二者存在显著的指数关系。没发现N₂O排放通量与温度及pH值间存在显著相关。稻田CH₄和N₂O排放受多种因素影响,但对全球变暖的贡献率CH₄远大于N₂O。NPKS处理的增温潜势最大,NPK处理的最小。     

Effects of various nitrogen fertilizers on emission of nitrous oxide from soils

Summary Field studies of the effects of different N fertilizers on emission of nitrous oxide (N20) from three Iowa soils showed that the N₂O emissions induced by application of 180 kg ha^–1 fertilizer N as anhydrous ammonia greatly exceeded those induced by application of the same amount of fertilizer N as aqueous ammonia or urea. On average, the emission of N₂O-N induced by anhydrous ammonia was more than 13 times that induced by aqueous ammonia or urea and represented 1.2% of the anhydrous ammonia N applied. Experiments with one soil showed that the N₂O emission induced by anhydrous ammonia was more than 17 times that induced by the same amount of N as calcium nitrate. These findings confirm indications from previous work that anhydrous ammonia has a much greater effect on emission of N₂O from soils than do other commonly used N fertilizers and merits special attention in research relating to the potential adverse climatic effect of N fertilization of soils.Laboratory studies of the effect of different amounts of NH₄OH on emission of N₂O from Webster soil showed that the emission of N₂O-N induced by addition of 100 g NH₄OH-N g^–1 soil represented only 0.18% of the N applied, whereas the emissions induced by additions of 500 and 1 000 g NH4OH-N g^–1 soil represented 1.15% and 1.19%, respectively, of the N applied. This suggests that the exceptionally large emissions of N₂O induced by anhydrous ammonia fertilization are due, at least in part, to the fact that the customary method of applying this fertilizer by injection into soil produces highly alkaline soil zones of high ammonium-N concentration that do not occur when urea or aqueous ammonia fertilizers are broadcast and incorporated into soil.     

Impacts of pellet pH on nitrous oxide emission rates from cattle manure compost pellets

Previous reports indicated that the emission of nitrous oxide (N₂O) when manure compost pellets (MCP) were applied to soil was greater than when ordinary manure compost or inorganic fertilizer was applied, but that applying pellets of nitrogen-enriched manure compost, a by-product of deodorizing manure during composting, resulted in N₂O emission rates less than those from MCPs. To investigate the mechanism by which N₂O emission rates and cumulative emissions were reduced in nitrogen-enriched manure composts pellets (N+MCP), we studied the impact of pellet pH on N₂O emission, because pH is different between MCP (pH 8.6) and N+MCP (pH 5.3). In an incubation experiment, the pH of pellets was adjusted to five levels (5.3, 6.0, 7.0, 8.0 and 8.6) with acid or alkaline solutions, and the pellets were incubated without soil in a beaker at 30°C for 90 d (MCP) or 42 d (N+MCP). A large peak in N₂O emission rate was observed soon after beginning the incubation (within 1–3 d) in the neutral and alkaline treatments for both MCP and N+MCP, and these peaks corresponded to a rise in the pellet nitrite contents. Thus, this N₂O emission peak might have been generated by the denitrification of nitrite in the pellets. In the acid treatments of MCP, the N₂O emission was distributed more in the later incubation period (14–90 d), when the reduction of nitrate in MCP occurred. This led to a significant increase in cumulative N₂O emission as compared with the alkaline treatments for MCP. Regarding the mechanism by which N₂O emission was reduced in N+MCP, although larger cumulative N₂O emission rates in the earlier stage (0–14 d for MCP and 0–7 d for N+MCP) were observed when the pellet pH was adjusted close to 7.0, lowering the pH of MCP to 5.3 (the pH of N+MCP) did not demonstrate a significant decrease in cumulative N₂O emission as compared with the original pH treatment (pH 8.6). These results indicate that pellet pH might not relate directly to the mechanism by which N₂O emission was reduced in N+MCP.     

Yield-scaled nitrous oxide emissions from nitrogen-fertilized croplands in China: A meta-analysis of contrasting mitigation scenarios

Nitrogen(N) losses in cropland resulting from the application of synthetic fertilizers decrease crop productivity and exacerbate environmental pollution.Mitigation measures, such as reduction in N fertilizer application rates, can have unintentional adverse effects on crop yield. We conducted a meta-analysis of soil N₂O emissions from agricultural fields across China under contrasting mitigation scenarios as a novel approach to identify the most effective strategy for the mitigation of emissions of N₂O derived from N fertilizer use in China. Current standard agricultural practice was used as a baseline scenario(BS), and 12 potential mitigation scenarios(S1–S12) were derived from the available literature and comprised single and combinations of management scenarios that accounted for crop yield. Mitigation scenarios S6(nitrification inhibitor 3,4-dimethylpyrazole phosphate) and S11(20% reduction in N application rate plus nitrification inhibitor dicyandiamide) in maize, rice, and wheat crops led to an average 56.0% reduction in N₂O emissions at the national level, whereas scenario S4(nitrification inhibitor dicyandiamide) led to yield optimization, with a 14.0% increase for maize and 8.0% increase for rice as compared to the BS. Implementation of these most effective mitigation scenarios(S4, S6, and S11) might help China, as a signatory to the 2015 United Nations Framework Convention on Climate Change(Paris Agreement), to achieve a 30% reduction in N₂O emissions by 2030.     

前期不同水分状况对土壤氧化亚氮排放的影响

田间采集的新鲜土壤样品分别在室温下风干(土样D)和淹水(土样S)保存110d后,将二者的含水量分别调至20%、40%、60%、80%、100%持水量(WHC,Water Holding Capacity),在25℃下培育138h,设置不通和通入10%(v/v)乙炔的处理。结果显示,在20%～80%WHC下培育时,土样S的氧化亚氮(N2O)排放量为土样D的2.48倍～6.36倍(p<0.01),而在100%WHC水分含量下培育时,土样S的N2O排放量仅为土样D的19%(p<0.01),通入乙炔不但未使土样D的N2O排放量增加,反而显著减少。通入乙炔的处理,培养结束后硝态氮的含量增加。随培育水分含量的升高,土样S和土样D的二氧化碳排放量增大。供试土样可能存在异养硝化作用。前期水分的差异显著影响土壤N2O排放量,故在田间测定土壤N2O排放量时,要考虑土壤前期水分的差异。     

秸秆还田对灌溉玉米田土壤反硝化及N2O排放的影响

运用乙炔抑制技术研究了不同施氮水平下秸秆还田对灌溉玉米田土壤反硝化反应和氧化亚氮(N2O)排放的影响。结果表明,土壤反硝化速率及N2O的排放受氮肥施用、秸秆处理方式及其交互作用的显著影响。与秸秆燃烧相比,不施氮或低施氮水平时,秸秆还田可刺激培养初期反硝化反应速率及N2O排放,增加培养期间N2O平均排放通量;高施氮水平时,秸秆还田可降低反硝化反应速率及反硝化过程中的N2O排放。秸秆还田可降低反硝化中N2O/N2的比例。     

控释肥施用对小麦生长期N2O排放的影响

通过田间试验,采用静态箱法研究不同施氮水平下控释肥和尿素(N 0、100、200、270 kg hm-2)对麦季N2O排放的影响。结果表明,与对照相比,整个小麦生长季N2O排放量均随尿素和控释肥施用量的增加呈指数增加(32%～164%,p<0.05),但控释肥处理增加程度则较尿素处理缓和;施用控释肥可以有效抑制小麦生长季N2O排放(p<0.05),控释肥对N2O的减排量随着施氮量的增加而增加。小麦产量随尿素施用量的增加呈抛物线增加(24%～43%,p<0.05),随控释肥施用量的增加亦呈抛物线增加(30%～45%,p<0.05);与施用相同水平尿素相比,施用控释肥的小麦产量略有增加,但无显著差异(p>0.05)。单位产量N2O排放量随尿素施用量的增加而呈指数增加(31%～114%,p<0.05),随控释肥施用量的增加而呈抛物线增加(2%～50%,p<0.05);施用控释肥可以有效抑制小麦生长季单位产量N2O排放(p<0.05),控释肥对单位产量N2O的减排量随着施氮量的增加而增加。各处理N2O排放量与土壤水分存在显著正相关(p<0.05),与土壤NH4+-N、NO3--N浓度和土温不呈明显线性关系(p>0.05)。     

The influence of winter soil cover on spring nitrous oxide emissions from an agricultural soil

In temperate regions, a majority of N₂O is emitted during spring soil thawing. We examined the influence of two winter field covers, snow and winter rye, on soil temperature and subsequent spring N₂O emissions from a New York corn field over two years. The first season (2006-07) was a cold winter (2309 h below 0 °C at 8 cm soil depth), historically typical for the region. The snow removal treatment resulted in colder soils and higher N₂O fluxes (73.3 vs. 57.9 ng N₂O-N cm⁻² h⁻¹). The rye cover had no effect on N₂O emissions. The second season (2007-08) was a much milder winter (1271 h below freezing at 8 cm soil depth), with lower N₂O fluxes overall. The winter rye cover resulted in lower N₂O fluxes (5.9 vs. 33.7 ng N₂O-N cm⁻² h⁻¹), but snow removal had no effect. Climate scenarios predict warmer temperature and less snow cover in the region. Under these conditions, spring N₂O emissions can be expected to decrease and could be further reduced by winter rye crops.     

农业微环境对土壤温室气体排放的影响

二氧化碳(CO     

保护地土壤N2O排放通量特征研究

为研究保护地土壤N2O排放通量特征,于2009年8～12月,在河北辛集不施氮（N0）、当地习惯施氮（N900）及减量施氮（N675）处理下的秋冬季番茄保护地土壤上使用静态箱采集、气相色谱仪检测的方法测定了土壤N2O排放通量。得到以下研究结果:灌溉施肥后,各处理N2O平均排放通量与表层土壤硝态氮含量呈极显著正相关关系。灌溉施肥后7 d内是施氮处理土壤N2O主要排放期,其排放量占当季总排放量的55.9%~59.8%;高峰值一般出现在第3～5 d,此时的土壤含水量对硝化、反硝化作用都较适宜。8～10月份由于温度较高,N2O排放通量明显高于较冷的11～12月。8～10月份施氮是影响保护地土壤N2O排放的主导因素,减少施氮量显著降低了N2O排放量;之后温度是主导因素,此时N2O排放量受追施氮量的影响较小。经估算,保护地秋冬季番茄不同施氮处理N2O总排放量的大小顺序为:N900（N 5.304 kg/hm2）N675（N 3.616 kg/hm2） N0（N 0.563 kg/hm2）,差异显著,减量施氮比习惯施氮处理降低了31.8%的N2O排放量;N675和N900处理的N2O排放系数分别为0.45和0.53。     

农用地定级因素法与修正法比较分析

以广东省惠阳市农用地定级研究为例，对因素法和修正法两种定级方法进行比较分析，论述了因素法和修正法的定级过程、应用特点、适用范围，以及定级成果的合理性。通过空间区分度(分异性)分析、空间重叠度(相同性)分析、级差收益分析和农用地等、级、价衔接分析，从不同方面论证了两种定级方法的可行性，认为修正法定级结果较符合当地实际。     

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.     

生物质炭对集约化菜地N2O排放和蔬菜产量的影响

【目的】 本试验评价了生物质炭对菜地土壤温室气体排放和产量的长期效应。 【方法】 田间试验在江苏省南京市集约化种植菜地进行。共设置4个处理,分别为对照 (CK)、单施氮肥处理 (N)、施用氮肥 + 新生物质炭 (NC_F,C_F在2016年6月施用) 以及施用氮肥 + 4年陈化生物质炭 (NC_A,C_A在 2012 年6月施用)。生物质炭施用量为40 t/hm2。2016年11月至2017年11月连续种植4季蔬菜,分别为小青菜、空心菜、苋菜、菠菜,并伴有休耕期。每季蔬菜施氮量均为N 240 kg/hm2,其中空心菜收获三茬,在第一茬收获后按照N 240 kg/hm2 追肥一次。采用静态暗箱–气相色谱法测定N₂O浓度。 【结果】 观测期内各处理菜地N₂O排放主要集中在第二季和第三季,其单位产量N₂O排放量分别为0.038～0.131 kg/t和0.107～0.482 kg/t,而第一季和第四季的单位产量N₂O排放量分别是0.033～0.209 kg/t和0.007～0.070 kg/t。土壤温度和矿质氮变化未显著影响土壤N₂O排放通量;整个观测期内土壤充水孔隙度 (WFPS) 介于37%～93%之间,土壤含水量变化显著影响 (P < 0.01) 土壤N ₂O排放通量。与N处理相比,整个轮作周期内NC_F和NC_A处理N₂O周年累积排放量和周年排放系数均显著降低,两个施生物质炭处理之间差异不显著;NC_F处理N₂O周年累积排放量和周年排放系数降幅分别为35.6%和46.2%,NC_A处理降幅分别达38.8%和49.9%。与N处理相比,NC_F和NC_A处理均增加了集约化菜地蔬菜产量,增幅分别为4.6%和17.9%,NC_A处理达到显著水平,两个施生物质炭处理之间差异不显著。此外,NC_F和NC_A处理分别显著降低单位产量N₂O排放量49.8%和41.3% (P < 0.01)。 【结论】 在集约化菜地土壤中经4年陈化后的生物质炭仍然具有较强的减排和增产能力。与新施入的生物质炭相比,施用4年后的生物质炭增产效果更显著;施用生物质炭对集约化蔬菜生态系统减排和改善作物生产具有长期效应。      

Effects of rate and depth of fertilizer application on emission of nitrous oxide from soil fertilized with anhydrous ammonia

Summary Field studies to determine the effect of different rates of fertilization on emission of nitrous oxide (N₂O) from soil fertilized with anhydrous ammonia showed that the fertilizer-induced emission of N₂O-N in 116 days increased from 1.22 to 4.09 kg ha^–1 as the rate of anhydrous ammonia N application was increased from 75 to 450 kg ha^–1. When expressed as a percentage of the N applied, the fertilizer-induced emission of N₂O-N in 116 days decreased from 1.6% to 0.9% as the rate of fertilizer N application was increased from 75 to 450 kg N ha^–1. The data obtained showed that a 100% increase in the rate of application of anhydrous ammonia led to about a 60% increase in the fertilizer-induced emission of N₂O.Field studies to determine the effect of depth of fertilizer injection on emission of N₂O from soil fertilized with anhydrous ammonia showed that the emission of N₂O-N in 156 days induced by injection of 112 kg anhydrous ammonia N ha^–1 at a depth of 30 cm was 107% and 21 % greater than those induced by injection of the same amount of N at depths of 10 cm and 20 cm, respectively. The effect of depth of application of anhydrous ammonia on emission of N₂O was less when this fertilizer was applied at a rate of 225 kg N ha^–1.