【作者】 张惠；

【导师】 杨正礼； 罗良国；

【作者基本信息】 中国农业科学院 ， 作物生态学， 2011， 博士

【摘要】 黄河上游灌区水稻中高产区过量施肥现象十分突出,氮肥过量引起土壤氮素盈余,对区域生态环境构成直接或潜在威胁。稻田氮素气态损失是灌区农田氮素流失的主要途径之一,氮肥过量施用加剧了氮素的气态损失,由氮素气态损失引起的大气氮沉降成为灌区地表水氮污染的重要来源,氮素气体排放引起的增温潜势不容忽视。为了实现灌区粮食增产和环境友好的双赢目标,迫切需要探明灌区稻田氮素的气态损失特征及减少氮素气态损失的有效途径。本研究选择黄河上游灌区具有代表性的宁夏引黄灌区灵武试验区,于2009-2010年开展大田小区试验和（15）^N微区示踪试验,通过大田原位监测,揭示了不同氮肥运筹下稻田氨挥发和N₂O排放的动态分布特征,估算了氮素气态损失量,评价了稻田氮素损失对环境的污染及大气增温效应;利用（15）^N示踪法及农田系统氮素质量平衡法,研究了稻田氮肥去向和稻田系统氮素平衡及损失风险。本研究田间小区试验设置了5个处理,分别为常规氮肥300 kg/hm2水平下的单施尿素（N300）和有机肥（猪粪）与尿素氮肥配合施用（N300-OM）的2个处理、优化氮肥240 kg/hm2水平下的单施尿素（N240）和有机肥（猪粪）与尿素氮肥配合施用（N240-1/2OM）的2个处理和不施氮肥（CK）处理。微区（15）^N示踪试验选择其中单施尿素的N300、N240和N0（CK）共3个处理。氨气的捕获采用密闭间歇式抽气,硼酸吸收,标准酸滴定法;N₂O气体采用密闭静态暗箱法采集、气相色谱法检测;同时在作物生长季监测雨水和灌溉水带入稻田的无机氮素。基于监测和测定值计算灌区稻田生长季氨挥发损失累积量和N₂O排放累积量,分析计算稻田氮素分布特征及氮素利用和损失。研究获得以下主要结论:1.黄河上游灌区稻田氮素氨挥发损失是氮素损失的主要途径之一。高氮肥施用会显著增加稻田氮素氨挥发损失量,有机肥配施及氮肥优化减量可显著降低稻田氨挥发损失量及肥料氮氨挥发损失百分率。在习惯灌水和习惯高氮肥300kgN/hm2水平下,稻田氨挥发损失氮素高达94.1 kgN/hm2,较其它处理差异显著（p < 0.05）;与N300处理比较,N300-OM处理的累积氨挥发损失量减少了17.4 kgN/hm2;优化施氮240kgN/hm2水平下,N240-1/2OM和N240处理的累积氨挥发损失量分别降低了22.7 kgN/hm2和26.5 kgN/hm2,方差分析差异显著（p < 0.05）。在黄河上游灌区习惯肥水管理水平下,投入稻田的肥料氮通过氨挥发损失量达66.5 kgN/hm2,通过氨挥发损失的肥料氮占施氮量的22.2%,灌区稻田每年通过氨挥发损失的氮素量高达1693.8×104 kg N/a,每年由稻田氨挥发损失形成的大气干湿沉降氮达1242.5×104¹524.4×104 kg N/a,稻田生长季每年由于氨挥发损失引起的大气干湿沉降氮,对灌区地表和水体的氮污染产生极大威胁。2.黄河上游灌区水稻生长季N₂O排放不是稻田氮素损失的主要途径,但其增温潜势不容忽视。灌区稻田不同施氮水平下,水稻整个生长季土壤N₂O排放总量为2.64³.87kg/hm2,肥料氮通过N₂O排放损失的百分率仅为0.43%⁰.64%。氮肥过量施用会显著增加N₂O排放量;在相同氮素水平下,有机肥配施会显著增加稻田N₂O的排放量;优化施氮能有效减少N₂O排放量（P<0.01）。在灌区习惯灌水和高氮肥300kg/hm2时,N300-OM处理的稻田N₂O排放量达3.87kg/hm2,在100a时间尺度上的全球增温潜势（GWPs）为20.76×107 kg CO₂/hm2;优化施氮240kg/hm2水平下,N240和N240-1/2OM处理的N₂O累计排放量与N300-OM处理比较,分别降低1.18kg/hm2和0.57kg/hm2,在100a尺度上每年由稻田N₂O排放引起的GWPs分别降低了3.30×107 kg CO₂/hm2和3.06×107 kg CO₂/hm2。3.水稻生长季氨挥发主要发生在分蘖肥和拔节肥后的2⁵d,稻田不同时期施肥灌水后第2³d氨挥发速率达最大值,不同处理的氨挥发速率最大值为5.80⁹.14 kg N/ （hm2·d）,在每次施肥后氨挥发持续时间为10d左右;N₂O排放主要发生在水稻插秧前及水稻生长的中后期,同时在稻田灌水泡田后及水稻生育中期土壤水分干湿交替时也有较大的排放量。高氮肥施用会显著增大氨挥发速率和N₂O排放通量,有机肥的配合施用会显著增加稻田N₂O累积排放量,但会适当降低稻田氨挥发损失量;土壤pH值对灌区稻田氨挥发影响较大,土壤pH值偏高导致稻田氨挥发损失氮量较其它地区严重,但pH值变化对N₂O排放通量影响不明显;此外温度、日照、降雨等因素变化对稻田氮素气态损失和排放也影响较大;稻田日氨挥发通量与稻田田面水NH4+-N浓度变化呈显著正相关,土壤N₂O排放通量与田面水NO3--N含量显著相关。4.灌区稻田高氮肥施用显著增加了土壤肥料氮残留量,导致土壤氮素大量盈余;优化施氮可显著提高植株对土壤氮的吸收量和氮肥农学利用率,有效减少肥料氮素土壤残留量,降低稻田土壤氮素盈余量。微区（15）^N同位素示踪试验结果表明,在灌区习惯灌水和习惯高氮肥300kgN/hm2水平下,水稻植株摄取肥料（15）^N的百分率为40%⁴2%,水稻植株对肥料（15）^N当季回收率（ηpf）为26.05%³0.43%,稻田土壤剖面0-90cm土体中氮肥残留率为17.9%²3.31%,肥料氮通过气态损失百分率达22.6%,灌区稻田氮肥表观损失率达47%⁵2%,由此得出,灌区稻田50%以上的氮肥离开农田系统,通过气态损失和灌溉淋溶损失,对大气、水体等造成直接污染。与习惯高氮肥处理相比,优化氮肥处理的水稻植株吸收的土壤氮量增加了12³5 kg/hm2,稻田土壤剖面0-90cm土体中标记肥料（15）^N残留量（Nsf）减少了32.83²6.74 kg/hm2,土壤氮素盈余量减少了22³1 kg/hm2。5.土壤剖面中（15）^N丰度变异特征分析表明,灌区稻田土壤氮素随灌溉水向土壤深层发生了淋溶迁移,水稻连作导致土壤氮素在60-90cm深度富集;灌区稻田高氮肥施用显著增加了土壤耕层0-30cm土层中肥料氮残留量,同时稻田连作导致土壤30cm以下肥料氮残留量显著增加。水稻生长季土壤剖面不同深度无机氮分布特征分析表明,氮肥施用对土壤剖面0-100cm无机氮累积量影响较大,高氮肥施用显著增加了稻田连作第二年插秧前土壤剖面硝态氮积累量,稻田基肥施用对0-40cm土体NH4+-N积累量影响最大。土壤表层铵氮积累量的增加,增大了氮素氨挥发损失的风险;土壤硝氮积累量的增加,导致稻田N₂O排放通量增加,同时也增大了稻田氮素淋溶损失的风险;优化施氮可有效降低土壤剖面无机氮的累积量,相应会减少稻田氨挥发损失和N₂O排放量,同时也会相应地降低土壤氮素深层淋溶损失的风险。稻田有机肥的施用可显著提高土壤无机氮的积累量,在满足水稻植株生长对氮素大量持续需求的同时,降低了氮素损失的风险。以上研究结果表明,在黄河上游灌区通过氮肥减量及有机肥配合施用等优化施氮措施可有效减少稻田氮素氨挥发损失,降低N₂O排放量,同时可显著提高稻田氮肥回收利用率,有效降低稻田土壤剖面硝态氮的深层积累和淋溶损失,保障黄河上游灌区大气、水体等生态环境安全。更多还原

【Abstract】 Input of nitrogen is essential for high crop yields, but losses of these same nutrients diminish environmental quality. Over-fertilization application in the irrigation area of the Yellow River where agricultural production is more developed are all faced with the serious situation of N pollution due to excessive fertilizer usage. Gaseous loss of N is a main way of nitrogen loss in the paddy fields of the irrigation area. Excessive application of nitrogen fertilizer increased the loss of gaseous nitrogen, as result of the increase of atmospheric nitrogen deposition into surface water, which has been an important source of nitrogen pollution in the irrigation area. All of these draw the high attention to the greenhouse effects by gaseous nitrogen emissions. Considering the high food production and the minimum environmental threat, we need to find an effective way to control the loss of gaseous nitrogen in the paddy fields of the irrigation area.The randomized split-plot experiments and the （15）^N tracing micro-plot experiment at the Lingwu farm of Ningxia irrigating area from 2009 to 2010 were conducted to get the patterns of the ammonia volatilization （AV） and N₂O emissions from the paddy field . The amount of the ammonia volatilization （AV） and N₂O emissions during the rice-growing season were also calculated. The fate of fertilizer derived nitrogen in the paddy field were estimated by the technique of stable isotope （15）^N-traced nitrogen fertilizer. With the mass balance method, we also estimated the nitrogen balance and risk of loss of N in the paddy field ecosystem.The five N treatments of field experiment were conducted, including two treatments of the conventional N application amount（300 kg/hm2）, i.e the application of only urea （N300） and the application of the organic fertilizer （manure） with the urea nitrogen （N300-OM）, two treatments of the optimized N application amount（240 kg/hm2）, i.e, the application of only urea （N240） and the application of the organic fertilizer （manure） with the urea nitrogen （N240-1/2OM）, and no nitrogen fertilizer application plot （CK）. Three treatments were conducted for the （15）^N tracing method with the micro-plot experiment, i.e, the application of only urea N300, N240, and CK.A batch-type airflow enclosure method was used to measure the AV, and analyzed with the boric acid absorption and the standard acid titration method. The static chamber-gas chromatograph method was used to measure the N₂O emission from the paddy field. Nitrogen from rainfall and irrigation water was measured in the experimental site as well. Based on both of the measuring data and the data from the experiments, we estimated the cumulative amount of AV and N₂O emissions in the rice growing season, and analyzed the nitrogen transport characteristics, nitrogen use efficacy and its loss from the rice field system.The main results are summed as follows:1. The AV is one of major way of nitrogen loss from the paddy fields of the irrigation area of the Yellow Rive. High nitrogen fertilizer can increase the N loss through AV. The application of organic fertilizer and reducing fertilizer use by optimized fertilization will reduce the loss of AV. The cumulative loss amount of AV reached 94.1 kgN/hm2 for conventional N application （N300）. Compared with N300, cumulative amount of AV of N300-OM treatment decreased by 17.4 kg/hm2 during the rice growing season. Compared with N300 treatment, cumulative loss of AV with N240-1/2OM and N240 treatmentwas reduced by 22.7 kg/hm2 and 26.5 kg/hm2, respectively. Nitrogen loss percentage through AV loss was reduced by 3.9 % to 5.5%. Under the conventional irrigation practice and high nitrogen fertilizer of 300kg/hm2, annual N losses due to AV from the rice filed in the irrigation area reached 1693.8×104 kg N/a, accounted for 22.2% of the fertilizer N applied.2. N₂O emissions from the paddy field is not an important way of nitrogen loss at the Yellow River irrigation area, but the warming potential through N₂O emissions in the irrigation area are not neglectable. Excessive application of N fertilizer in the paddy field will significantly increase N₂O emissions, and at the same level of nitrogen application, organic fertilizer amendment could increase N₂O emissions from the paddy soil （P < 0.01）. Optimization of nitrogen application in the irrigated paddy field during the rice growing season could reduce N₂O emissions. At the rice growing stage, N₂O emissions mainly occurred before the tiller stage or at the pre- and late- rice growth stages and more N₂O emissions were measured after rice planting and irrigation. At different nitrogen levels, the total amount of N₂O emissions during the whole rice growing season varied among 2.64 3.87kg/hm2, and the loss of fertilizer nitrogen by N₂O emissions was only 0.43% 0.64%. With the conventional irrigation practice and high nitrogen fertilizer of 300kg/hm2, N₂O emissions from paddy fields in N300-OM treatment reached 3.87 kg/hm2. In the scales of 100a, the global warming potential （GWPs） was 20.76×107 kg CO₂/hm2. Compared with N300-OM treatment, cumulative N₂O emissions in N240 and N240-1/2OM treatments decreased by 1.18 kg/hm2 and 0.57 kg/hm2, respectively. In the scales o100a, GWPs caused by N₂O emissions in the paddy field decreased 3.30×107 kg CO₂/hm2 and 3.06×107 kg CO₂/hm2, respectively.3. Ammonia volatilization during the rice growing season mainly occurred 2⁵d after the tillering and jointing fertilier applied. Nitrogen loss through AV in N300 treatment at tillering and jointing stages accounted for 30.4% and 29.9% of N application, respectively; Nitrogen loss through AV in N300-OM treatment at tillering and jointing stages accounted for 16.8%¹8.5% of N application. Compared with N300 treatment, the percentage of fertilizer N losses decreased by 13.6% and 11.4%. Ammonia volatilization loss from basal fertilizer was relatively large, the percentage lost of different treatments were 11.2% to 14.5%, AV rate reached its maximum at 2³d after fertilization or irrigation at different stages, at a rate of 5.8⁹.14 kg N / （hm2 ? d）, which was affected mainly by N application amount, and temperature, sunshine time, rainfall and pH value also have significant influence on it.4 The results with the （15）^N tracing technique showed that the high N fertilizer application increased the N uptake by rice from fertilizer, and the amount of N rice absorbed from soil reduced correspondingly, which resulted in the higher N surplus in soil. Under the conventional irrigation and fertilizer management level, the （15）^N-labbled fertilizer recovery in rice plant （ηpf） was 26.05%-30.43%. In the paddy soil profiles of 0-90cm, the residual of （15）^N-labeled fertilizer in soil （Nsf） were 53.70-69.93 kg/hm2, and N residual rate in soils were 17.9%²3.31%. Coupled with the method of N balance, the apparent loss of N from the paddy field was 47%-52%, of which N loss as gaseous from the paddy fields was 22.6%. Optimization of nitrogen fertilizer can significantly reduce the amount of N surplus and N loss from the paddy field. Compared with N300, optimized N fertilizer application could decrease the loss of fertilizer N by 26.74-32.83 kg/hm2, and reduce the amount of N surplus by 22- 31 kg/hm2.5. The distribution of （15）^N abundance variability in different soil profile indicated that in the N300 treatment, 55% of the nitrogen left in the 0-90cm soil enriched in the 0-30cm topsoil. As a result of continuous yearly rice planting, fertilizer N leached into deep soil layers along with irrigation water. The （15）^N-labelled fertilizer was detected in the 60-90cm soil layer, indicating that nitrogen fertilizer has leached below 90cm. The nitrogen fertilizer may have entered the shallow groundwater during the growing season. The analysis of changing characteristics of inorganic N accumulation showed high-level nitrogen fertilizer application significantly increased the concentration of ammonium N and nitrate content in top 0-20cm soil. Optimization can reduce the N accumulation in soil layer. Application of organic manure significantly increased nitrate accumulation in 0-100cm soil, and increased the leaching risk of nitrogen loss, as well as N₂O emissions. The N application reduction, optimization of organic manure treatment and other measures can effectively reduce nitrogen loss through AV and N₂O emissions in the paddy field at the irrigation area of Yellow River, and significantly increase nitrogen recycling rate in the paddy field.更多还原