农田土壤N2O生成与排放影响因素及N2O总量估算的研究

综述了国内外农田土壤N2 O生成与排放及其影响因素、N2 O排放测定技术及总量估算等方面的研究进展 ,指出硝化与反硝化过程均可产生N2 O ,而影响硝化、反硝化过程的土壤水分含量、温度、pH、有机碳含量和土壤质地等是影响农田土壤N2 O生成与排放的重要因素。根据我国各地农田土壤N2 O排放通量测定结果及相应模型分析 ,初步估算全国农田土壤N2 O年排放总量为N 398Gg ,约占全球农田土壤排放总量的 1 0 % ,其中旱田N2 O年排放总量为N 31 0Gg ,水田为N 88Gg。     

水分状况对水田土壤N2O排放的影响

通过室内培养试验,研究了不同水分含量下水稻土的Ｎ２Ｏ排放,结果表明,在水分含量相当于田间持水量时,土壤具有最大的Ｎ２Ｏ排放速率,当水分含量在田间持水量之上时,反硝化作用是Ｎ２Ｏ的主要来源。水分含量在田间持水量之下时,尽管硝倾作用强烈,但Ｎ２Ｏ排放量较小。通过温室盆栽试验研究了不同水分管理措施下,水稻土Ｎ２Ｏ和ＣＨ４的排放,同常规水分管理方式相比,长期淹水显著增加ＣＨ４的排放而减少了Ｎ２Ｏ的排放。相反,湿润灌溉的处理在整个水稻生长期内没有明显的ＣＨ４排放,但其Ｎ２Ｏ排放对水分状况敏感,出现数次峰值,从而总排放量远高于其它两处理。     

黄土性土壤剖面中N2O排放的研究初报

用田间原位土壤探头测定法和乙炔抑制未扰动土柱法 ,对黄土性土壤N2 O的排放进行了研究。试验结果表明 ,黄土性土壤N2 O的排放量存在着明显的季节和空间变异。季节变化与田间水分因子密切相关 ,N2 O高峰常出现在灌水 (降水 ) 3天后 ,施肥处理和对照的趋势完全一致。全年中八月份各土层N2 O浓度最高 ;在最高峰值时 ,施肥处理的N2 O浓度几乎是对照处理的 2 .5倍。土壤剖面中N2 O的浓度的顺序是 1 0cm <30cm <1 50cm <90cm <60cm ,以 60～90cm土层最高。影响黄土性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。     

外源碳对鄂南棕红壤N2O排放的影响

   探讨不同水分条件下土壤 N₂O 排放对外源碳添加的响应,明确N₂O排放与碳源的关系,为农田土壤N₂O减排提供理论依据。   设置不添加碳源（C0）、按2 g kg⁻¹含碳量添加葡萄糖（C1）、蔗糖（C2）、甘露醇（C3）共4个不同处理,同时设置低水分（W1）和高水分（W2）两个水分条件,所有处理均添加等量氮肥,在室温25 ℃下培养一周,测定不同处理的土壤N₂O排放通量、CO₂排放通量以及土壤无机氮含量。通过统计分析,揭示外源碳和不同水分处理对鄂南棕红壤N₂O排放的影响。   在不同水分条件下,外源碳的添加降低了土壤NO₃⁻-N含量和NH₄ ⁺ -N含量。土壤水分显著影响土壤N₂O的排放,高水分处理土壤N₂O的排放高于低水分处理。与对照相比,添加葡萄糖、蔗糖、甘露醇处理在低水分条件下的土壤N₂O-N累积排放量分别增加352.15倍、393.07倍、93.94倍;在高水分条件下,添加葡萄糖、蔗糖、甘露醇处理的土壤N₂O-N累积排放量分别增加1.92倍、0.63倍、1.88倍。   3种外源碳输入显著促进土壤N₂O排放总量,其中以添加葡萄糖的处理 N₂O排放最高,高水分条件下土壤N₂O排放远高于低水分处理。     

抑制剂对海南土壤中硝化作用及N2O排放的影响

通过室内培养试验研究4种肥料增效剂对尿素在海南土壤中氮素转化和N₂O排放的影响,以期筛选出适合海南土壤的氮肥增效剂类型。培养试验设单施尿素（CK）、尿素 + 长效复混肥添加剂（加入尿素量的8‰,NAM）、尿素 + 双氰胺（加入尿素量的3.5%,DCD）、尿素 + 3,4-二甲基吡唑磷酸盐（加入尿素量的1%,DMPP）、尿素 + 2-氯-6-三氯甲基吡啶（加入尿素量的8‰,NMAX）5个处理。在培养过程中定期测定土壤理化性质、铵态氮和硝态氮含量以及N₂O排放量的变化,以分析不同增效剂对土壤氮素形态及N₂O排放的影响。结果表明:添加增效剂处理土壤的pH、有机质、全氮和速效钾等均与CK无显著差异,但土壤速效磷含量显著降低。培养过程中,除DCD外,DMPP、NAM和NMAX处理铵态氮浓度一直处于较低水平,而土壤硝态氮含量缓慢增长,显示出明显的硝化抑制效果。与CK处理相比,添加抑制剂处理土壤N₂O浓度峰值延后,累计排放量显著降低,但不同抑制剂间差异不显著。综合比较硝化抑制作用及N₂O减排效果,可以认为添加长效复混肥添加剂（NAM）、3,4-二甲基吡唑磷酸盐（DMPP）和2-氯-6-三氯甲基吡啶（NMAX）等抑制剂的肥料适宜应用于海南水稻土。     

肥料添加剂降低N2O排放的效果与机理

如何降低氮肥施入农田后的N2O排放,实现氮肥增产效应的同时降低其对环境的负面影响是全球集约化农业生产中重要的科学问题,氮肥添加剂是有效途径之一。本研究采用室内静态培养法,在调节土壤水分含量和温度等环境因素的条件下,研究不同肥料添加剂对华北平原典型农田土壤N2O排放的影响及其机制。结果表明,N2O排放通量的峰值大约出现在施氮后的第24 d,肥料混施较肥料表施的出峰时间提前。与单施尿素处理相比,添加硝化抑制剂DMPP或DCD能分别降低N2O排放总量99.2%和97.1%; 添加硫酸铜对N2O排放的抑制作用不显著; 添加秸秆会增加N2O排放总量60.7%,而在添加秸秆的土壤中施加硝化抑制剂DMPP能够显著降低N2O排放量至无肥对照水平。说明华北平原农田土壤中N2O的产生主要是由硝化作用驱动,同时也可看出,添加硝化抑制剂是N2O减排的有效措施。     

土壤水分状况对CH4氧化,N2O和CO2排放的影响

实验室培育试验表明,土壤氧化ＣＨ４,排放Ｎ２Ｏ和ＣＯ２的最佳水分含不量。水稻土氧化ＣＨ４的最佳水分含同于半干旱草地土壤,均接近于土壤环境常年水分含量。水稻土Ｎ２Ｏ排放量随着水分含量的下降而增加,半干旱草地土壤则随着水分含量的下降而减少,表明背离土壤环境上水分含量越远,Ｎ２Ｏ的排放量越大。因而,ＣＨ４氧化和Ｎ２Ｏ排放对土壤水分含量的反应呈极显著的负相关性。ＣＯ２排放的最佳水分含量接近或高于ＣＨ４氧化     

玉米地土壤反硝化速率与N2O排放通量的动态变化

应用乙炔抑制原状土柱培育法测定了4种施肥处理的玉米地N素反硝化损失速率和氧化亚氮（N2O）排放通量,并分析了它们与土壤湿度、土壤温度以及硝态氮（NO3^-－N）含量之间的关系,计算了因反硝化和N2O排放造成的N肥损失率。结果表明,玉米生育期内土壤N素的反硝化损失量为0．67－3．85kg/hm^2,N肥的反硝化损失率为0．5％－1．5％;土壤N2O排放总量为0．55－1．42kg/hm^2,N肥的N2O排放系数为0．2％－0．5％。     

原位条件下不同土壤中N2O的通量

本文研究了原位条件下3种土壤中氧化亚氮的通量。结果表明,湖积物发育的潜育性水稻土施用硝酸铵时,水稻苗期土壤释放氧化亚氮的通量为5.71微克N/平方米·秒;第四纪红色粘土发育的红壤性水稻土(潴育性)和黄泛沉积物发育的淹育性水稻土(石灰性)施用硝酸钾时,水稻苗期土壤释放氧化亚氮的通量分别为9.57和1.53微克N/平方米·秒。湿润条件下,石灰性水稻土硝化过程释放氧化亚氮的通量为1.75微克N/平方米·秒。     

温度对旱田土壤N2O排放的影响研究

以南方亚热带代表性旱田土壤－贵州玉米－油菜轮作田、大豆－冬小麦轮作田和休耕地为研究对象,同步观测了整轮作期土壤N2O排放通量和温度的季节变化。同时,采用DNDC模型定量探讨了未来气温变化对土壤N2O排放的潜在影响。结果表明,温度是土壤N2O排放通量规律性日变化的最主要控制因素;除大豆地外,其他作物生长季节和休耕地的N2O排放通量季节变化与温度之间均存在一定程度的正相关性,其中冬季休耕地的N2O排放通量与温度间存在弱指数函数关系。模型检验结果表明,除大豆地外,其余试验地的N2O排放通量均随年均气温升高而升高,在冬春季,土壤N2O排放通量对气温变化的敏感性强于夏秋季,尤其以冬春季休耕地受体气温变化的影响最为显著。     

Cassava (Manihot Esculenta Crantz) Yields,Soil Nitrous Oxide Emission,and Soil Nitrogen Transformation Affected by Nitrification Inhibitors in Loamy Sand Soil in Thailand

The effects of nitrification inhibitors (NIs) on soil nitrous oxide (N₂O) emission, soil ammonium (NH₄⁺) and nitrate (NO₃^?), and cassava (Manihot esculenta Crantz) yields were investigated in a loamy sand soil in eastern Thailand. Treatments were chemical fertilizer (CF) and CF plus dicyandiamide (DCD) or neem (Azadirachta indica) oil at two rates of 5% and 10%. DCD had a greater reduction of soil N₂O flux than the neem oil (P<0.10). DCD and neem oil retained NH₄⁺-N in the soil by 79% and 63% (P ≤ 0.10), respectively. The NI effect on soil NO₃^?-N was small due to a low N fertilizer rate. The cassava root yield and N uptake were increased 4–11% and 2–18%, respectively, by use of NIs, but they were only significant for DCD (P ≤ 0.10). These findings suggest that NIs application may be a promising method for minimizing nitrogen loss and enhancing crop yields in a tropical cassava field.     

Background level of nitrous oxide in the atmosphere in relation to flux from soil

According to Broadbent and Clark (3), there are numerous data indicating that denitrification leads to the emission of N₂O together with N₂, whereby loss of N is developed from soils. Nitrous oxide is also released from soils to the atmosphere during the nitrification of ammonium and ammonium-producing fertilizers under aerobic conditions (1). Relatively few attempts have been made to directly measure N₂O evolution under field conditions (6, 7, 10–12), although a number of laboratory studies have been reported. These studies are essential for determining the N balance between additions and losses of soil N.     

区分土壤中硝化与反硝化对N2O产生贡献的方法

土壤是产生N₂O的最主要来源之一。硝化和反硝化反应是产生N₂O的主要机理,由于硝化和反硝化微生物同时存在于土壤中,因而硝化和反硝化作用能同时产生N₂O。N₂O的来源可通过使用选择性抑制剂,杀菌剂以及加入的标记底物确定。通过对生成N₂O反应的每一步分析,主要从抑制反应发生的催化酶和细菌着手,总结了测量区分硝化、反硝化和DNRA反应对N₂O产生的贡献方法。并对¹⁵N标记底物法,乙炔抑制法和环境因子抑制法作了详细介绍。     

不同利用方式红壤反硝化势和气态产物排放特征

采用厌氧培养-乙炔抑制法测定了4种不同利用方式红壤的反硝化势和气态产物N₂O和N₂的排放速率。结果表明,不同利用方式红壤反硝化势和N₂O和N₂的排放速率差异明显,土壤反硝化势强弱顺序依次为：竹林>茶园>林地>旱地。反硝化势与土壤有机碳(P<0.05)、厌氧培养期间土壤CO₂累积排放量(P<0.01)、nirS基因丰度( P<0.05)和nirK基因丰度(P<0.05) 呈显著正相关关系。逐步回归分析结果表明,CO₂累积排放量表征的易矿化碳是造成不同利用方式红壤反硝化势差异的主要原因,可以解释反硝化势变化的66%(P<0.01)。不同利用方式红壤N₂O和N₂排放速率差异明显,旱地红壤N₂O和N₂排放速率均最低,表明土壤pH的提升并没有增加旱地红壤的反硝化损失风险和N₂O排放速率。土壤易矿化有机碳含量也是影响不同利用方式红壤N₂O和N₂排放速率的主要因素。反硝化功能基因nirS、nirK和nosZ的丰度均与CO₂累积排放量呈显著正相关关系,进一步支持了土壤易矿化有机碳含量是影响不同利用方式红壤反硝化势和气态产物排放的主要因子。土壤pH是影响不同利用方式红壤反硝化气态产物N₂/N₂O的主要因素,但是pH影响红壤N₂/N₂O的微生物机制仍需要进一步研究。     

华北平原水浇玉米-小麦轮作农田氨挥发与反硝化损失

Ammonia (NH3) volatilization, denitriflcation loss, and nitrous oxide (N2O) emission were investigated from an irrigated wheat-maize rotation field on the North China Plain, and the magnitude of gaseous N loss from denitrification and NH3 volatilization was assessed. The micrometeorological gradient diffusion method in conjunction with a Bowen Ratio system was utilized to measure actual NH3 fluxes over a large area, while the acetylene inhibition technique (intact soil cores) was employed for measurement of denitrification losses and N2O emissions. Ammonia volatilization loss was 26.62% of the applied fertilizer nitrogen (N) under maize, while 0.90% and 15.55% were lost from the wheat field at sowing and topdressing, respectively. The differences in NH3 volatilization between different measurement events may be due to differences between the fertilization methods, and to differences in climatic conditions such as soil temperature. Denitrification losses in the fertilized plots were 0.67%-2.87% and 0.31%-0.49% of the applied fertilizer N under maize and wheat after subtracting those of the controls, respectively. Nitrous oxide emissions in the fertilized plots were approximately 0.08%-0.41% and 0.26%-0.34% of the applied fertilizer N over the maize and wheat seasons after subtracting those of the controls, correspondingly. The fertilizer N losses due to NH3 volatilization were markedly higher than those through denitriflcation and nitrous oxide emissions. These results indicated that NH3 volatilization was an important N transformation in the crop-soil system and was likely to be the major cause of low efficiencies with N fertilizer in the study area. Denitriflcation was not a very important pathway of N fertilizer loss, but did result in important evolution of the greenhouse gas N2O and the effect of N2O emitted from agricultural fields on environment should not be overlooked.     

Nitrous oxide production at different soil moisture contents in an arable soil in China

Abstract

Laboratory incubations were conducted to investigate nitrous oxide (N₂O) production from a subtropical arable soil (Typic Plinthodults) incubated at different soil moisture contents (SMC) and with different nitrogen sources using a 10% (v/v) acetylene (C₂H₂) inhibitory technique at 25°C. The production of N₂O and CO₂ was monitored during the incubations and changes in the contents of KCl-extractable NO^? ₃-N and NH⁺ ₄-N were determined. The production of N₂O increased slightly with an increase in SMC from 40% water-holding capacity (WHC) to 70% WHC, but increased dramatically at 100% WHC. After incubation the NO^? ₃-N content increased even at a SMC of 100% WHC. At a SMC of 100% WHC, the addition of NH⁺ ₄-N promoted the production of N₂O and CO₂, whereas the addition of NO^? ₃-N decreased N₂O production. Compared with the incubation without C₂H₂, the presence of C₂H₂ increased NH⁺ ₄-N content, but decreased NO^? ₃-N content, and there was no significant difference in N₂O production. These results indicate that heterotrophic nitrification contributes to N₂O production in the soil.