【作者】 林忠成；

【导师】 戴其根； 张洪程；

【作者基本信息】 扬州大学 ， 农产品安全与环境， 2010， 博士

【摘要】 太湖地区是我国著名的农业高产区之一,以稻麦两熟为主,种植历史悠久。近年来,太湖水系水体氮、磷偏高,富营养化问题日益突出,农业面源污染受到广泛关注。该农区稻麦两熟种植体系中,氮肥投入量一直较高,过量施肥普遍,不仅肥料利用率低,而且在土壤—作物系统中氮素持续盈余,导致土壤背景氮较高。因此,从土壤—作物系统中研究氮素利用与平衡特点,以及高产与环境改善的要求,研究适宜的土壤背景氮和适宜的施氮量,对于太湖地区稻麦两熟氮素养分科学管理,降低氮素面源污染具有十分重要的理论与实践意义。本研究针对太湖地区土壤高背景氮的现状,通过施氮与不施氮耗竭的定位试验,研究施氮量与土壤背景氮对作物产量、土壤剖面氮素积累与运移、氮肥利用效率等方面的影响,期望明确维持地力、环境保护与稻麦高产、氮高效协调的适宜施肥量。试验于2007-2009年进行,2007年麦季在太湖周边地区的吴江、溧阳、宜兴、武进、常熟和相城(太湖地区农科所)等代表性农田,按0~20cm、20~40cm、40~60cm、60~80cm和80~100cm土壤剖面分层取样,研究了土壤剖面养分特征和对无机氮素的吸附特性。在此基础上,2007-2009年在太湖地区典型农区吴江市,进行3年5季(第1、2、3、4、5季分别为稻、麦、稻、麦、稻季,第6季小麦仍在进行中)稻麦轮作不施氮耗竭与施氮的组合3年定位试验,设养分不施氮耗竭区(不施氮肥区)、施氮肥区(5个水平)。以稻麦周年施纯氮量,施氮肥区全年施纯氮量分别为0(不施氮肥区,即耗竭区)、175、350、525、700、875 kg/hm2,水稻和小麦的施氮量分别占57%和43%,即稻季分别为0、100、200、300、400、500 kg/hm2,麦季分别为0、75、150、225、300、375 kg/hm2。氮肥均用尿素。水稻的氮肥运筹方式为基肥、分蘖肥、穗肥分别在倒4叶期与倒2叶期四次等量施用,小麦的氮肥运筹方式为基肥与拔节孕穗肥,二者比例为6:4。试验过程为2007年进行第一季水稻试验,以稻麦为一周年单位,第一年度(2007年)设置不施氮肥耗竭区和施氮肥区(5个水平);第二年度(2008年)施氮肥区仍按上年度施氮水平继续进行,而经1年(2008年5月份小麦收获后)的不施氮肥耗竭区上分别设置不施氮肥耗竭区和施氮肥区(5个水平);第三年度(2009年),施氮肥区、不施氮耗竭1年后再施氮的小区仍按上年度施氮水平继续进行,而经2年(2009年5月份小麦收获后)的不施氮肥耗竭区上分别又设置不施氮肥耗竭区和施氮肥区(5个水平)。不施氮耗竭区面积在2007年按3年定位试验所需提前规划好。与此同时,在扬州大学试验基地运用土壤渗漏池(Lysimeter),系统研究了在砂土和黏土上稻麦两熟土壤—作物系统中田面水氮、氨挥发、氮素渗漏、作物吸收和土壤剖面氮素累积等氮素行为与数量特征。主要研究结果如下:1、太湖流域各县市的耕地土壤氮素含量高于省平均值,其中上层土壤全氮和速效氮含量最高,土壤氮素含量随着土壤剖面深度的增加而减小;各种土壤的不同剖面对铵态氮的吸附量不同,黏土的吸附能力高于砂性土壤,下层土壤的吸附能力高于上层;随着铵态氮浓度的增大,土壤对铵态氮吸附量都表现为增大的趋势。2、稻季氨挥发量取决于施氮后田面水NH4+-N浓度,与当次施氮量有关,均随着施氮量的增加而增大,且在施氮后1~3天左右达最大值,田面水NH4+-N浓度和氨挥发峰值同步出现,施氮后一周是减少氨挥发、防止径流氮损失的关键期;黏性土壤的氨挥发损失比例要低于砂性土壤,黏土氨挥发总损失量为10.49~87.06 kg/hm2,占施氮量的比例10.92%~21.76%,砂土氨挥发总损失量为11.32~102.43 kg/hm2,占施氮量的比例11.32%~25.61%;各次施氮后氨挥发损失量的大小依次为分蘖肥>倒4叶穗期>基肥>倒2叶穗肥,发现稻季施氮量300 kg/hm2时氨挥发量比200 kg/hm2跃增。氮素渗漏主要泡田引起,以NO3--N为主,NH4+-N很少,砂土NO3--N的渗漏多于黏土,高氮处理NO3--N的渗漏要高于低氮处理,渗漏量大的土壤要高于渗漏量小的土壤。3、土壤—作物系统不同施氮量持续施用,以及不施氮耗竭1、2年后施氮在不同施氮量条件下,各季水稻产量对当季不同施氮量的响应有明显的差异,呈现出土壤背景氮对产量的效应明显,水稻持续施氮处理当季施氮量为100 kg/hm2和200 kg/hm2时,3年水稻产量呈降低趋势,说明土壤不施氮耗竭使背景氮减小,水稻不能获得高产;当施氮量为300 kg/hm2时,持续施氮和不施氮耗竭1、2年后施氮均能获得最高产量;而高于300 kg/hm2时均引起水稻倒伏减产,所以土壤的水稻高产适宜施氮量趋于当季300 kg/hm2、周年525 kg/hm2,可以维持水稻高产的土壤背景氮。水稻累积吸氮量也呈一定的土壤背景效应,氮肥利用率随当季施氮量的增加而降低,与土壤背景氮关系不密切。4、小麦季土壤剖面中无机氮素含量不仅与当季施氮量有关,还与土壤肥力背景值有关,各个生育期土壤剖面无机氮素主要集中在0~30 cm土层,且随着施氮量增加而增加,30~100 cm土层无机氮素对施氮量300~375 kg/hm2有明显地响应,拔节期以后已有明显的淋溶效应;施氮量300~375 kg/hm2土壤中无机氮素的残留量一直较高,小麦成熟期土壤无机氮量与播种期相比,施氮量375 kg/hm2处理仍在增加,施氮量小于300 kg/hm2处理均有所减少;小麦—土壤系统氮素表观损失量随着施氮量的增加而增大,施氮处理75 kg/hm2和375 kg/hm2的损失量和损失率(占相应施氮量的比例)分别为26.20 kg/hm2、34.93%,168.64 kg/hm2、44.97%。从小麦各个生育阶段氮素的损失情况来看,播种至返青期氮素表观损失最多,且随着施氮量的增加而增大,因此要控制前期基肥的施用量;拔节至开花期小麦吸肥量最多,低氮处理(75 kg/hm2和150 kg/hm2)出现氮素亏缺,而高氮处理(300 kg/hm2和375 kg/hm2)氮肥表观损失依然较高,土壤中一直存在着较多的无机氮素;小麦施氮量不超过225 kg/hm2较为适宜。5、土壤剖面氮素含量主要在耕作层,土壤氮素含量随着土壤深度的增加呈减小趋势,在土壤层次40~50cm处达到最小值,尔后略有增大趋势,不施氮处理土壤剖面氮素含量要比试验前减小,呈现氮素养分耗竭的作用;一旦施氮土壤耕作层的氮素含量对氮肥有响应,且随着施氮量的增加而增大,下层土壤氮素也增大,低氮处理(年施氮量为175 kg/hm2和350 kg/hm2)增加较少,而高氮处理(年施氮量为700 kg/hm2和875 kg/hm2)土壤剖面氮素含量显著增大;第五季作物水稻收获后不施氮耗竭2年后施氮处理的土壤剖面氮素含量要低于不施氮耗竭1年后施氮处理和持续施氮处理的相应处理;小麦季土壤剖面氮素含量特别是上层土壤要显著低于水稻季,耗竭效应对旱季小麦的产量影响作用较大;当季施氮均能改变土壤氮素含量,且与施氮量相关。本研究在稻麦较高产的条件下,兼顾氮肥利用效率,综合考虑水稻季施氮后氨挥发效应、土壤氮素渗漏特点和小麦季土壤剖面无机氮素的变化等研究结果表明,太湖流域获得当前生产上水稻目标产量9750 kg/hm2和小麦目标产量6000 kg/hm2,水稻的适宜施氮量为225~300 kg/hm2,小麦的适宜施氮量为180~225 kg/hm2,较有利于维持地力、稻麦高产、氮相对高效和生态安全。更多还原

【Abstract】 Taihu Lake region is one of the most famous agriculture areas of high yield in China; its rice-wheat double cropping system has a long history. In recent years, the concentration of N and P in water of Taihu Lake is on the high side, the eutrophication of surface waters is increasing seriously, non-point source pollution from agriculture have attracted considerable attention. Nitrogen application rate in rice-wheat double cropping system of Taihu Lake district was always higher. Owing to the long-term excessive use of nitrogen, this not only results in the lower nitrogen use efficiency, but also increases nitrogen surplus in soil-crop system, causing higher content of background nitrogen in soil. So the utilization and balance characteristic of nitrogen in soil-crop system, the aim of higher crops yield and the improvement of environment, the appropriate content of background nitrogen in soil and nitrogen application rate were studied. These researches had great theoretical and practical significance to the scientific management of nitrogen nutrient in rice-wheat double cropping system of Taihu Lake district, and to the decrease of non-point nitrogen pollution to our environment.This research based on the current situation of higher content of background soil nitrogen in Taihu Lake region, by doing some experiments about the location of nitrogen application and the exhaustion of nitrogen, the efficiency of nitrogen application rates and content of background soil nitrogen on crop yield, the accumulation and transmission of nitrogen in soil profile, nitrogen use efficiency and so on were studied. With the appropriate amount of nitrogen application, with the appropriate nitrogen application rate, the research aimed at keeping the harmonions relationship among the condition of earth, the protection of environment, the higher yield of rice and wheat and the higher use efficiency of nitrogen. From 2007 to 2009 the experiments were carried out. In the wheat season of year 2007, the researchers took samples of soil profile with the layer of 0～20cm、20～40cm、40～60cm、60～80cm and 80～100cm from the representative farmland in counties of Wujiang, Liyang, Yixing, Wujin, Changshu, Xiangcheng, and then analysed the nutrient characteristic of soil profile and its adsorption characteristic. On this basis, from 2007 to 2009, the located experiments of nitrogen application and nitrogen exhaustion in the rotation of rice and wheat about five crop seasons which were rice-wheat-rice-wheat-rice from first season to fifth season and sixth wheat was growing in three years were carried out in the experimental station of Farming and Forestry Bureau of Wujiang county, Suzhou city, Jiangsu province, China. There were the areas of nitrogen exhaustion (without nitrogen treatments) and areas of nitrogen application (with five nitrogen application rates). According to the amount of pure nitrogen application in rice-wheat system in one year, the treatments of different nitrogen application rate were 0, 175, 350, 525, 700 and 875 kg/ha, the nitrogen fertilizer was divided into 57% for rice and 43% for wheat, so the nitrogen application rate for rice were 0, 100, 200, 300, 400 and 500 kg/ha, and for wheat were 0, 75, 150, 225, 300 and 375 kg/ha, the nitrogen fertilizer was all urea. The nitrogen application of rice was that basal fertilizer, tillering fertilizer, ear fertilizer in four leaves from top panicle stage and two leaves from top panicle stage were applied equally for four times. The use of nitrogen for wheat was that 60% in basal fertilizer and 40% in jointing stage by broadcasting. The experimental process was that first rice experiment was stated in 2007, an anniversary cropping of rice and wheat was a unit. According to the design, in 2007, there were five nitrogen application areas and the others were no nitrogen application areas. After the harvest of rice, the wheat sowed in the corresponding areas for the same experimental purposes. In 2008, to the nitrogen application areas, the experiments of 2008 were continued on the base of 2007, meanwhile, five studies about the quantity of nitrogen application were carried out on these areas, and also some areas were continuously kept to do experiments without nitrogen. The experiments of 2009 were carried out in the same ways like in 2008. The areas of nitrogen exhaustion were programmed before the year of 2007. At the same time, by using the soil Lysimeter in the experimental base of Yangzhou university, the nitrogen behavior and quantity characteristics in soil-crop system of rice-wheat rotation, such as the dynamic changes of NH4+-N concentration in surface water, ammonia volatilization and the leaching of nitrogen in soil after applying nitrogen fertilizer in rice season, the accumulation of nitrogen of crop and the dynamic changes of inorganic nitrogen in soil profile in wheat season were studied. The main results were as follows.First, the nitrogen content of cultivated land in each county around Taihu Lake Region was higher than the average standard of Jiangsu province. In the surface soil, the content of total nitrogen and available nitrogen were the highest, but they decreased when the depth of soil increased. To different soil’s different layers, the amount of NH4+-N absorption was,different, the absorption ability of clay soil was higher than sandy soil, and the NH4+-N absorption ability of subsoil was higher than surface soil. With the increase of NH4+-N concentration, the NH4+-N absorption ability of soil increased too.Second, in rice season, the amount of ammonia volatilization losses depended on the density of NH4+-N in surface water and also related to the nitrogen application rate, the amount of ammonia volatilization losses and the density of NH4+-N in surface water all increased as the nitrogen application rate increased. The quantity turned to the peak in 1~3 days after applying the nitrogen, and the highest density of NH4+-N and amounts of ammonia volatilization losses appeared at the same time, one week after applying the nitrogen was the key time to reduce the nitrogen loss of ammonia volatilization and runoff. The loss of ammonia volatilization in clay soil was lower than that in sandy soil, the total loss of ammonia volatilization from clay soil was 10.49~87.06 kg/ha, and the proportion to nitrogen application rate was 10.92%~21.76%; the total loss of ammonia volatilization from sandy soil was 11.32~102.43 kg/ha, and the proportion to nitrogen application rate was 11.32%~25.61%. After applying different stages of nitrogen fertilizers, the ammonia volatilization losses were that the tillering stage > four leaves from top panicle stage > basal stage > two leaves from top panicle stage, and also we found that when the nitrogen application rate about 300 kg/ha in rice season, the amount of ammonia volatilization was higher than that about 200 kg/ha. Nitrogen leaching was mostly brought by flooding the farmland, NO3--N was the main form of nitrogen in leaching waters, NH4+-N was very little. The leaching of NO3--N in sandy soil was more than that in clay soil, the leaching of NO3--N which with higher nitrogen application was more than that with lower nitrogen application, and the leaching of NO3--N in the soil which owns higher leaching ability was more than that owns lower leaching ability.Third, different nitrogen application rates in soil-crop system were applied continuously and applied after one year and two years’exhaustion, the response of rice yield to nitrogen application rate was obvious different, it presented that the domino effect of content of background nitrogen in soil on rice yield was distinctness. When the amount of nitrogen application were 100 kg/ha and 200 kg/ha, the rice yield decreased in three years, it showed that soil nitrogen exhaustion made the content of background nitrogen decrease, we couldn’t get high rice yield. When the nitrogen application rate was 300 kg/ha, the treatments of nitrogen applied continuously and applied after one year and two years’exhaustion all got high yield. But when the nitrogen application rate went even higher than that point, the rice plants lodged and yield decreased. So the nitrogen application rate in which rice got high yield was 300 kg/ha in a season and 525 kg/ha in one year, it would keep the content of background nitrogen which could ensure the high yield of rice. The content of background nitrogen in soil had some effect on nitrogen absorption accumulation of rice. The use efficiency of nitrogen fertilizer decreased when the nitrogen application rate increased, it were not related to the content of background nitrogen in the soil.Forth, the inorganic nitrogen in soil profile (INISP) in wheat season was not only related to the nitrogen application rate (NAR), but also to the background nitrogen level in the soil. The INISP mostly concentrated at the depth of 0-30 cm of the soil and increased as the NAR increased at different growth stages of wheat, the inorganic nitrogen at the depth of 30~100 cm of the soil had an obvious response to the NAR when the amount was in the range of 300 kg/ha to 375 kg/ha, and it had obvious eluviations effect after jointing stage; when the NAR was in the range of 300 kg/ha to 375 kg/ha, the remains of INISP was always higher, compared with the sowing stage, the INISP in maturity stage increased only when was given the treatment that the NAR was 375 kg/ha, otherwise, it all decreased when the NAR was smaller than 300 kg/ha. In wheat-soil system, the apparent losses of nitrogen increased as the NAR increased. When the NAR was 75 kg/ha, the amount of loss and rate of loss were 26.20 kg/ha and 34.93%; when the NAR was 375 kg/ha, the amount of loss and rate of loss were 168.64 kg/ha and 44.97%. According to the nitrogen loss of different stages of wheat, the nitrogen loss was most from sowing to returning green stage, which increased as the NAR increased, so the basal fertilizer should be limited. The wheat absorbed more nitrogen from jointing to flowering stage, the treatment with lower nitrogen application appeared deficiency, but the nitrogen loss of higher nitrogen application treatment was still severe, there were more inorganic nitrogen in soil. That nitrogen application rate didn’t exceed 225 kg/ha was suitable in wheat season.Fifth, nitrogen content in soil profile (NCISP) was mostly in the cultivation soil, with the increase of soil’s depth, the NCISP decreased, it reached the minimum at the soil depth of 40~50cm, and then increased slightly. NCISP was lower than before which was under the treatment without nitrogen, it’s because of exhaustion effect. Once being applied nitrogen fertilizer, the nitrogen content in the cultivation soil responded to the nitrogen application rate, it increased as the increase of nitrogen application rate, nitrogen of subsoil was also increasing. NCISP under the lower nitrogen treatment which nitrogen application rate was 175 kg/ha and 350 kg/ha in a year increased a little, but NCISP under the higher nitrogen treatment which nitrogen application rate was 700 kg/ha and 875 kg/ha in a year increased significantly. After the fifth harvest of rice, the NCISP under the nitrogen treatment which applied after two years soil exhaustion was lower than both after one year soil exhaustion and continuous nitrogen treatment. In wheat season, the NCISP especially in the surface soil was obvious lower than that in rice season. The effect of soil exhaustion was stronger to wheat yield. Seasonal nitrogen application would change soil nitrogen content, and it was related to nitrogen application rate.Synthesizing all the results of this research, in the condition of higher yield, giving attention to the nitrogen use efficiency, ammonia volatilization losses, the leaching of NO3--N in the soil, the change of inorganic nitrogen in soil profile in wheat season, it was indicated that in Taihu Lake region, if you wanted to achieve the aim of 9750 kg/ha for rice yield and 6000 kg/ha for wheat yield at present, the appropriate nitrogen application rate for rice was 225~300 kg/ha, and 180~225 kg/ha for wheat. With the appropriate nitrogen application rate, the content of background nitrogen in soil would keep steady, crops would get higher yield, nitrogen would get comparatively higher use efficiency and environment would be in a secure state.更多还原