上海郊区蔬菜田氮素流失的研

Nitrogen （N） leaching in vegetable fields from December 2002 to May 2003 with equal dressings of total N for a sequential rotation of Chinese flat cabbage （Brassica chinensis L. var. rosularis） and lettuce （Lactuca sativa L.） in a suburban major vegetable production base of Shanghai were examined using the lysimeter method to provide a scientific basis for rational utilization of nitrogen fertilizers so as to prevent nitrogen pollution of water resources. Results showed that leached N consisted mainly of nitrate N, which accounted for up to more than 90% of the total N loss and could contribute to groundwater pollution. Data also showed that by partly substituting chemical N （30%） in a basal dressing with equivalent N of refined organic fertilizer in the Chinese flat cabbage field, 64.5% of the leached nitrate N was reduced, while in the lettuce （Lactuca sativa L.） field, substituting 1/2 of the chemical N in a basal dressing and 1/3 of the chemical N in a top dressing with equivalent N of refined organic fertilizers reduced 46.6% of the leached nitrate N. In the twoyear sequential rotation system of Chinese flat cabbage and lettuce, nitrate-N leaching in the treatment with the highest amount of chemical fertilizer was up to 46.55 kg ha^-1, while treatment plots with the highest amount of organic fertilizer had only 17.58 kg ha^-1. Thus, partly substituting refined organic fertilizer for chemical nitrogen in the first two seasons has a great advantage of reducing nitrate-N leaching.     

太湖地区水稻最适宜施氮量研究

To determine the optimal amount of nitrogen(N) fertilizer for achieving a sustainable rice production at the Taihu Lake region of China,two-year on-farm field experiments were performed at four sites using various N application rates.The results showed that 22%-30% of the applied N was recovered in crop and 7%-31% in soils at the rates of 100-350 kg N ha 1.Nitrogen losses increased with N application rates,from 44% of the applied fertilizer N at the rate of 100 kg N ha 1 to 69% of the N applied at 350 kg N ha 1.Ammonia volatilization and apparent denitrification were the main pathways of N losses.The N application rate of 300 kg N ha 1,which is commonly used by local farmers in the study region,was found to lead to a significant reduction in economic and environmental efficiency.Considering the cost for mitigating environmental pollution and the maximum net economic income,an application rate of 100-150 kg N ha 1 would be recommended.This recommended N application rate could greatly reduce N loss from 199 kg N ha 1 occurring at the N application rate of 300 kg N ha 1 to 80-110 kg N ha 1,with the rice grain yield still reaching 7 300-8 300 kg DW ha 1 in the meantime.     

15N标记的包膜尿素在华北平原渗滤系统中的回收和淋失

The effectiveness of polyolefin-coated urea (Meister-5 and Meister-10; CU) in a wheat (Triticum aestivum L.)-maize (Zea mays L.) rotation system was studied in lysimeter plots located in the North China Plain for three consecutive maize- wheat-maize cropping seasons. An isotopic method was used to compare the fate of CU to that of non-coated urea (NCU), and N application rates of 0, 100, 150 and 225 kg N ha-1 were evaluated. The results showed that the nitrogen use effciency (15NUE) of CU was 13.3%–21.4% greater than that of NCU for the first crop. Alternatively, when the difference method was applied (apparent NUE), no significant variations were observed among treatments in all three seasons. Although inorganic N leached from the 1.3 m layer was less than 1% of the total applied N, unidentified losses of 15N (losses of 15N = 15N applied as fertilizer – 15N absorbed by crops – 15N remaining in the 0–0.2 m layer – 15N leached from the 1.3 m layer) in CU-treated plots were 24.2%–26.5% lower than those of NCU-treated plots. The nitrate concentration in the 0–1.3 m layer of CU plots at the end of the experiment was 53% lower than that of NCU-treated plots. Thus, CU increased crop N uptake from fertilizer and reduced unidentified losses of applied N, which can reduce the risk of groundwater pollution.     

太湖水稻土麦季尿素氨挥发损失

Ammonia volatilization losses from urea applied as a basal fertilizer and a top dressing at tillering stage in a wheat field of Taihu Region, China, were measured with a micrometeorological technique. Urea as fertilizer was surface broadcast at 81 (low N) and 135 (high N) kg N ha-1 as basal at the 3-leaf stage of the wheat seedling on December 2002, and 54 (low N) and 90 (high N) kg N ha-1 as top dressing on February 2003. Ammonia volatilization losses occurred mainly in the first week after applying N fertilizer and mainly during the period after basal fertilizer application, which accounted for more than 80% of the total ammonia volatilization over the entire wheat growth period. Regression analysis showed that ammonia volatilization was affected mainly by pH and NH4^ -N concentration of the surface soil and air temperature.Ammonia volatilization flux was significantly correlated with pH and NH4^ -N concentration of the surface soil and with daily air average temperature and highest temperature. Thus, application of urea N fertilizer to wheat should consider the characteristics of ammonia volatilization in different periods of N application so as to reduce ammonia losses.     

中国太湖地区稻麦轮作农田硝态氮动态与氮素平衡

Nitrate-nitrogen (NO 3--N) dynamics and nitrogen (N) budgets in rice (Oryza sativa L.)-wheat (Triticum aestivum L.) rotations in the Taihu Lake region of China were studied to compare the effects of N fertilizer management over a two-year period. The experiment included four N rates for rice and wheat, respectively: N1 (125 and 94 kg N ha-1 ), N2 (225 and 169 kg N ha-1 ), N3 (325 and 244 kg N ha-1 ), and N0 (0 kg N ha-1 ). The results showed that an overlying water layer during the rice growing seasons contributed to moderate concentrations of NO 3--N in sampled waters and the concentrations of NO 3--N only showed a rising trend during the field drying stage. The NO 3--N concentrations in leachates during the wheat seasons were much higher than those during the rice seasons, particularly in the wheat seedling stage. In the wheat seedling stage, the NO 3--N concentrations of leachates were significantly higher in N treatments than in N0 treatment and increased with increasing N rates. As the NO 3--N content (below 2 mg N L-1 ) at a depth of 80 cm during the rice-wheat rotations did not respond to the applied N rates, the high levels of NO 3--N in the groundwater of paddy fields might not be directly related to NO 3--N leaching. Crop growth trends were closely related to variations of NO 3--N in leachates. A reduction in N application rate, especially in the earlier stages of crop growth, and synchronization of the peak of N uptake by the crop with N fertilizer application are key measures to reduce N loss. Above-ground biomass for rice and wheat increased significantly with increasing N rate, but there was no significant difference between N2 and N3. Increasing N rates to the levels greater than N2 not only decreased N use efficiency, but also significantly increased N loss. After two cycles of rice-wheat rotations, the apparent N losses of N1, N2 and N3 amounted to 234, 366 and 579 kg N ha-1 , respectively. With an increase of N rate from N0 to N3, the percentage of N uptake in total N inputs decreased from 63.9% to 46.9%. The apparent N losses during the rice seasons were higher than those during the wheat seasons and were related to precipitation; therefore, the application of fertilizer should take into account climate conditions and avoid application before heavy rainfall.     

中国南方稻麦轮作生态系统中土壤溶解性有机氮的淋失

The rice-wheat rotation in southern China is characterized by frequent flooding-draining water regime and heavy nitrogen(N)fertilization. There is a substantial lack of studies into the behavior of dissolved organic nitrogen(DON) in the intensively managed agroecosystem. A 3-year in situ field experiment was conducted to determine DON leaching and its seasonal and yearly variations as affected by fertilization, irrigation and precipitation over 6 consecutive rice/wheat seasons. Under the conventional N practice(300kg N ha-1for rice and 200 kg N ha-1for wheat), the seasonal average DON concentrations in leachate(100 cm soil depth) for the three rice and wheat seasons were 0.6–1.1 and 0.1–2.3 mg N L-1, respectively. The cumulative DON leaching was estimated to be1.1–2.3 kg N ha-1for the rice seasons and 0.01–1.3 kg N ha-1for the wheat seasons, with an annual total of 1.1–3.6 kg N ha-1. In the rice seasons, N fertilizer had little effect(P 0.05) on DON leaching; precipitation and irrigation imported 3.6–9.1 kg N ha-1of DON, which may thus conceal the fertilization effect on DON. In the wheat seasons, N fertilization had a positive effect(P 0.01)on DON. Nevertheless, this promotive effect was strongly influenced by variable precipitation, which also carried 1.8–2.9 kg N ha-1of DON into fields. Despite a very small proportion to chemical N applied and large variations driven by water regime, DON leaching is necessarily involved in the integrated field N budget in the rice-wheat rotation due to its relatively greater amount compared to other natural ecosystems.     

中国云南省滇池盆地东南区由于土地利用方式的变化（从水田变为旱地或温室土壤）导致土壤理化性质的变化研究

Paddy fields in the southeastern basin of Dianchi Lake have rapidly changed to greenhouses since 1999. A total of 61 surface soil samples, including 43 greenhouse soils, 12 upland soils, and 6 paddy soils, were collected from a flat lowland area mainly used for agricultural production fields in the southeastern basin of Dianchi Lake. Analyses of the soil samples indicated that the greenhouse soils were characterized by a lower organic matter content, lower pH, and higher soluble nutrients than the paddy soils in the area. The lower organic matter content of the greenhouse soils was ascribed to environmental or management factors rather than the clay content of the soil. Accumulation of soluble nutrients, especially inorganic N, was due to over-application of fertilizers, which also caused soil acidification. The average amount of readily available N, P, and K accumulated in the greenhouse soils was estimated to be equal to or higher than the annual input of these nutrients as a fertilizer, indicating that a reduction in fertilizer application was possible and recommended. In contrast, a very low available Si content was observed in the paddy soils, suggesting the need for Si application for rice production.     

施肥深度和用量对华南果园土壤氮磷流失的影响

Fertilizers are heavily applied in orchards of the hilly and mountainous topography of South China and may increase nutrient loadings to receiving waters. A simple runoff collecting system was used to measure the effects of different fertilization treatments on total N and P concentrations of surface runoff in a Chinese chestnut （Castanea mollissima Blume） orchard in Dongyuan County, Guangdong Province, China. In such orchards, fertilizer was typically applied in two short furrows or pits on either side of each tree. Treatments included three application depths （surface, 10 cm and 20 cm）, and three application rates （low, median and high）. Results showed that 90.5% of the runoff water samples had a total N concentration higher than 0.35 mg·L^-1 and 54.2% had a total P concentration higher than 0.1 mg·L^-1. Fertilizer application at all depths and at all but the lowest rate significantly increased total N and P concentrations in runoff water. Fertilization with chemical compound fertilizer at a soil depth of 20 cm produced significantly lower （P 〈 0.05） total N concentration in runoff than both surface and 10-cm depth fertilization, and significantly lower （P 〈 0.05） total P concentration in runoff than surface fertilization. Total N and P concentrations in runoff significantly increased with the application rate of organic fertilizers. With the exception of total P concentrations, which were not significantly different between the control and fertilization at a rate of 119 kg P ha-1 in organic form, all the other fertilization treatments produced significantly higher total N and total P concentrations in runoff than the control. A fertilization depth ≥ 20 cm and an application rate ≤ 72 kg N ha-1 or 119 kg P ha^-1 for compound organic fertilizer was suggested to substantially reduce N and P runoff losses from hillslope orchards and to protect receiving waters in South China.     

保护地蔬菜轮作体系中两种不同复合肥对产量的影响及其氮素动态特征

Yield and N uptake of tomato (Lycopersicum esculentum Mill.) and pepper (Capsicum annuum L.) crops in five successive rotations receiving two compound fertilizers (12-12-17 and 21-8-11 N-P₂O₅-K₂O) were studied to determine 1) crop responses, 2) dynamics of NO₃-N and NH₄-N in different soil layers, 3) N balance and 4) system-level N efficiencies. Five treatments (2 fertilizers, 2 fertilizer rates and a control), each with three replicates, were arranged in the study. The higher N fertilizer rate, 300 kg N ha^-1 (versus 150 kg N ha^-1), returned higher vegetable fruit yields and total aboveground N uptake with the largest crop responses occurring for the low-N fertilizer (12-12-17) applied at 300 kg N ha^-1 rather than with the high-N fertilizer (21-8-11). Ammonium-N in the top 90 cm of the soil profile declined during the experiment, while nitrate-N remained at a similar level throughout the experiment with the lower rate of fertilizer N. At the higher rate of N fertilizer there was a continuous NO₃-N accumulation of over 800 kg N ha^-1. About 200 kg N ha^-1 was applied with irrigation to each crop using NO₃-contaminated groundwater. In general, about 50% of the total N input was recovered from all treatments. Pepper, relative to tomato, used N more efficiently with smaller N losses, but the crops utilized less than 29% of the fertilizer N over the two and a half-year period. Local agricultural practices maintained high residual soil nutrient status. Thus, optimization of irrigation is required to minimize nitrate leaching and maximize crop N recovery.     

Responses of Agronomic Benefit and Soil Quality to Better Management of Nitrogen Fertilizer Application in Greenhouse Vegetable Land

As a result of intensive greenhouse vegetable production in northern China, the potential risk of nitrogen (N) fertilizer over-applied is increasingly apparent and is threatening ecosystem and the sustainability of food production. An experiment was carried out in Shouguang, Shangdong Province, China to evaluate agronomic benefit and soil quality under different N applications, including the conventional chemical N rate (1000 kg N ha-1 season-1, N1), 70% of N1 (N2), 70% of N1 + maize straw (N3), 50% of N1 + maize straw + drip irrigation (N4), and 0% of N1 (N0), during two successive growing seasons of autumn-winter (AW) and winter-spring (WS). The maximum yields for N4 were 1.1 and 1.0 times greater than those for N1 in the AW and WS seasons, respectively. N agronomic effciency (AEN) and apparent N recovery effciency (REN) were greatest with the N4. A significant relationship was found between soil NO-3 -N content and electrical conductivity (EC) (R2 = 0.61 in the AW season and R2 = 0.29 in the WS season). Reducing N fertilizer decreased soil NO-3 -N accumulation (20.9%-37.8% reduction in the AW season and 11.7%-20.1% reduction in the WS season) relative to the accumulation observed for N1 within the 0-100 cm soil layer. Soil urease and invertase activities were not significantly different among N treatments. The N4 treatment would be practical for reducing excess N input and maintaining the sustainability of greenhouse-based intensive vegetable systems in Shouguang.     

施氮量对太湖地区设施菜地年氮素淋失的影响

采用田间小区试验,研究了太湖地区设施菜地一年三季作物（番茄-莴苣-芹菜）氮素淋失特征。结果表明：太湖地区设施菜地氮淋失以NO3--N为主,氮素淋洗量受施氮量的直接影响,以农民习惯施氮量（N5）处理下的淋洗总量最高,全年TN淋失总量高达193.6 kg.hm-2。在N5基础上减施N 40%（N3）可分别减少番茄、莴苣和芹菜季TN淋洗损失40.4%、49.2%和57.5%,同时可分别增产15.1%、39.0%和27.8%。设施菜地氮素淋洗高峰发生在揭棚期（7—11月）,其中包括揭棚休闲期和莴苣生长前期。揭棚期淋洗液TN平均浓度为51.1 mg.L-1,是盖棚期TN浓度的1.7倍;TN淋洗量为129.2 kg.hm-2,约占全年总氮淋洗量的66.7%。     

华南受干扰林和成熟林氮素流失对模拟氮沉降的响应

Current nitrogen (N) leaching losses and their responses to monthly N additions were investigated under a disturbed pine (Pinus massoniana) forest and a mature monsoon broadleaf forest in southern China. N leaching losses from both disturbed and mature forests were quite high (14.6 and 29.2 kg N ha^-1 year^-1, respectively), accounting for 57% and 80% of their corresponding atmospheric N inputs. N leaching losses were substantially increased following the first 1.5 years of N applications in both forests. The average increases induced by the addition of 50 and 100 kg N ha^-1 year^-1 were 36.5 and 24.9 kg N ha^-1 year^-1, respectively, in the mature forest, accounting for 73.0% and 24.9% of the annual amount of N added, and 14.2 and 16.8 kg N ha^-1 year^-1 in the disturbed forest, accounting for 28.4% and 16.8% of the added N. Great N leaching and a fast N leaching response to N additions in the mature forest might result from long-term N accumulation and high ambient N deposition load (greater than 30 kg N ha^-1 year^-1 over the past 15 years), whereas in the disturbed forest, it might result from the human disturbance and high ambient N deposition load. These results suggest that both disturbed and mature forests in the study region may be sensitive to increasing N deposition.     

两个氮素利用率不同的水稻品种根系形态及生理特性的差异

The variation in nitrogen (N) uptake by rice has been widely studied but differences in rice root morphology that may contribute to this variation are not completely understood. Field and greenhouse experiments were carried out to study N accumulation, root dry weights, total root lengths, root surface areas, and root bleeding rates of two rice cultivars, Elio with low N-use efficiency and Nanguang with high N-use efficiency. Low (1 mmol N L^-1) and high (5 mmol N L^-1) N applications were established in the greenhouse experiment, and the N rates were 0, 120, and 240 kg ha^-1 in the field experiments at Jiangning and Jiangpu farms, Nanjing, China. The results showed that the N accumulation, root dry weight, total root length, and root surface area increased with an increase in N application. At the heading stage, N accumulation in the shoots and roots of Nanguang was greater than that of Elio in the field experiments and that of Elio at 5 mmol N L^-1 in the greenhouse experiment. After the heading stage, N accumulation was higher for Nanguang at both 1 and 5 mmol N L^-1 in the greenhouse experiment. The total root length and root surface area were significantly different between the two cultivars. Over the range of the fertilizer application rates, the root lengths of Nanguang at Jiangning Farm were 49%-61% greater at booting and 26%-39% greater at heading than those of Elio, and at Jiangpu Farm they were 22%-42% and 26%-38% greater, respectively. Nanguang had a greater root bleeding rate than Elio. It was concluded that the N-use efficiency of the two rice cultivars studied depended to a great extent on the root morphological parameters and root physiological characteristics at different growth stages.     

氮肥用量对太湖水稻田间氨挥发和氮素利用率的影响

Ammonia volatilization losses, nitrogen utilization efficiency, and rice yields in response to urea application to a rice field were investigated in Wangzhuang Town, Changshu City, Jiangsu Province, China. The N fertilizer treatments, applied in triplicate, were 0 （control）, 100, 200, 300, or 350 kg N ha^-1. After urea was applied to the surface water, a continuous airflow enclosure method was used to measure ammonia volatilization in the paddy field. Total N losses through ammonia volatilization generally increased with the N application rate, and the two higher N application rates （300 and 350 kg N ha^-1） showed a higher ratio of N lost through ammonia volatilization to applied N. Total ammonia loss by ammonia volatilization during the entire rice growth stage ranged from 9.0% to 16.7% of the applied N. Increasing the application rate generally decreased the ratio of N in the seed to N in the plant. For all N treatments, the nitrogen fertilizer utilization efficiency ranged from 30.9% to 45.9%. Surplus N with the highest N rate resulted in lodging of rice plants, a decreased rate of nitrogen fertilizer utilization, and reduced rice yields. Calculated from this experiment, the most economical N fertilizer application rate was 227 kg ha^-1 for the type of paddy soil in the Taihu Lake region. However, recommending an appropriate N fertilizer application rate such that the plant growth is enhanced and ammonia loss is reduced could improve the N utilization efficiency of rice.     

节水控肥下有机无机肥配施对日光温室黄瓜–番茄轮作体系土壤氮素供应及迁移的影响

本试验以日光温室秋冬茬番茄-冬春茬黄瓜轮作体系为研究对象,采用田间小区试验,研究了5季节水控肥（冬春茬黄瓜和秋冬茬番茄季N-P2O5-K2O总投入量分别为600-300-525 kg/hm2和450-225-600 kg/hm2）有机无机肥配施对 040 cm（根区）土壤硝态氮供应、 40100 cm（根区以外）硝态氮残留和 0100 cm土体不同形态氮素淋失的影响,探索了设施蔬菜生产中节水节肥潜力,为构建设施蔬菜合理水肥管理下土壤肥力培育和土壤质量提升模式提供技术支持。试验结果表明, 1）农民习惯水肥管理节水节肥潜力较大; 节水控肥后0100 cm土体硝态氮积累量、 矿质氮和有机氮渗漏量均明显下降,种植蔬菜经济效益显著增加。2）商品有机肥猪粪与化肥在土壤无机氮供应方面的效果接近; 节水控肥1/41/2 猪粪氮替代1/41/2 化肥氮后,040 cm土体硝态氮供应和40100 cm土体硝态氮残留均无显著变化,但是随着猪粪氮配施比例的增加,土壤溶液渗漏量及养分淋失量呈增加趋势。3）施用秸秆促进了土壤无机氮固持,降低根区土壤硝态氮供应水平,提高土壤养分保蓄能力; 节水控肥1/2秸秆氮替代1/2化肥氮后,040 cm土壤硝态氮供应量平均下降34.3%~56.2%,40100 cm土体硝态氮残留量下降42.5%~87.8%, 0100 cm土体土壤溶液渗漏量下降65.0%,硝态氮淋失量下降 82.0%,而产量和经济收入无显著差异。根据本试验结果,对于新建温室可采用单施化肥、 化肥与猪粪配施方案,能在短时间内提高土壤无机氮供应强度,满足蔬菜氮素需求; 对于种植了一段时间的温室,可采用冬春茬黄瓜季化肥配施猪粪秋冬茬番茄季化肥配施秸秆方案,能固定积累于土壤中的无机氮,提高土壤养分容量,保证根层土壤氮素的稳定供应,降低环境风险,维护设施农业的可持续发展。     

天津市设施菜地施肥现状及减施潜力和对策

  【目的】  设施菜地存在施肥量过大、肥料利用率低、环境污染等问题。通过对天津市设施菜地施肥现状调查,明确设施菜地施肥现状和存在问题,为制定科学合理的施肥方案提供依据。  【方法】  本研究对天津市193个设施蔬菜地块施肥现状展开调查,明确设施菜地施肥特征,估算肥料总养分和化肥养分减施潜力。  【结果】  天津市日光温室平均养分施用总量为N 775.6 kg/hm2、P₂O₅ 715.5 kg/hm2和K₂O 524.9 kg/hm2,显著大于塑料大棚对应养分平均施用总量N 670.9 kg/hm2、P₂O₅ 584.5 kg/hm2和K₂O 425.3 kg/hm2 (P < 0.05)。有机肥是设施菜地养分的主要来源,对日光温室和塑料大棚N、P₂O₅和K₂O各自施用总量的贡献均超过50%。日光温室和塑料大棚中,化肥对磷 (P₂O₅) 施用量的贡献分别为44.2%和48.8%。从养分施用方法看,N、P₂O₅和K₂O基施比例日光温室分别为79.4%、80.2%和73.5%,塑料大棚分别为70.2%、78.2%和67.4%,P₂O₅基施比例大于N和K₂O。日光温室和塑料大棚平均养分施用比例 (N∶P₂O₅∶K₂O) 分别为1.00∶0.92∶0.69和1.00∶0.87∶0.63。相比推荐施肥量,天津市设施蔬菜N和P₂O₅普遍施用过量,甘蓝和白菜K₂O投入不足。设施菜地总养分 (N + P₂O₅ + K₂O) 减施潜力在31.5%～65.0%,化肥养分减施潜力在22.4%～66.6%。  【结论】  天津市设施菜地养分以基施为主,其中化肥基施比例偏高,追肥养分比例过低,养分总量过量施用现象普遍。设施菜地基施化肥和追肥中P₂O₅比例偏高,养分结构不合理。主要设施蔬菜中,茄子、番茄和芹菜的N和P₂O₅施用总量远超过各自推荐施肥量,化肥养分减施潜力较大,是设施蔬菜肥料减施关注的重点。     

包膜尿素对玉米和小麦的生物学与环境效应

应用渗滤池研究了褐潮土不同用量包膜尿素(POCU)和普通尿素对小麦玉米轮作条件下作物生长发育和地下水污染的影响。结果表明,施用包膜尿素可以显著提高玉米的产量、吸氮量和氮肥利用率;小麦收获期土壤残留氮也明显高于普通尿素处理。玉米的氮肥利用率(55%～140%)明显高于小麦(29.96%4～5.26%)。在每季作物施尿素和包膜尿素N.1002～25.kg/hm2的条件下,地下水淋溶损失的硝态氮量只占施肥量的0.43%1～.12%,表明在目前施肥水平下,中国北方实行的小麦玉米轮作制,一般不存在化肥氮素的淋溶损失。     

太湖地区稻麦轮作下氮素径流和淋洗损失

Although nitrogen （N） loss through runoff and leaching from croplands is suspected to contribute to the deterioration of surrounding water systems, there is no conclusive evidence for paddy soils to prove this hypothesis. In this study, field plot experiments were conducted to investigate N losses through runoff and leaching for two consecutive years with 3 N fertilization rates in rice （Oryza sativa L.）-wheat （Triticum aestivum L.） rotations in the Taihu Lake region, China. A water collection system was designed to collect runoff and leachates for both the rice and wheat seasons. Results showed that dissolved N （DN）, rather than particulate N （PN）, was the main form of N loss by runoff. The NO3^--N concentration in runoff was between 0.1 and 43.7 mg L^-1, whereas the NH4^＋-N concentration ranged from below detection limit to 8.5 mg L^-1. Total N （TN） loads by runoff were 1.0-17.9 and 5.2-38.6 kg ha^-1 during rice and wheat seasons, respectively, and the main loss occurred at the early growing stage of the crops. Nitrogen concentrations in leachates during the rice seasons were below 1.0 mg L^-1 and independent of the N application rate, whereas those during the wheat season increased to 8.2 mg L^-1 and were affected by the fertilizer rate. Annual losses of TN through runoff and leaching were 13.7-48.1 kg ha^-1 from the rice-wheat cropping system, accounting for 5.6%-8.3% of the total applied N. It was concluded that reduction in the N fertilization rate, especially when the crop was small in biomass, could lower the N pollution potential for water systems.     

不同水肥措施下华北露地菜地氮淋溶特征

华北地区典型一年两季露地蔬菜种植系统,蔬菜生长季水热同季、种植管理中水氮供应充足且往往过量,造成大量氮素淋溶到深层土壤,不仅造成水肥资源利用率低,对地下水质也造成威胁。本文以华北潮褐土黄瓜-白菜一年两季典型露地蔬菜为研究对象,利用田间试验研究不同氮肥用量及优化措施(包括抑制剂、生物炭、秸秆还田)以及控制灌溉量对蔬菜产量、土壤氮淋溶及氮平衡的影响。研究结果表明:1)华北典型露地菜地氮肥主要损失去向为深层土壤中积累及氮淋溶。2)农民常规施肥处理[黄瓜季和白菜季各施550 kg(N)·hm~(-2)]淋洗出80cm土壤剖面的总氮占当季氮肥施用量的10.0%,减氮20%和50%分别使总氮淋溶量降低23.8%和45.6%;减氮20%对蔬菜产量没有显著影响,减氮50%对水肥需求量较高的黄瓜产量有显著影响(减产19.6%)。3)减氮20%配合脲酶抑制剂和硝化抑制剂、施用生物炭和添加秸秆还田分别使全年总氮淋溶量比常规水肥处理降低40.7%、43.0%和34.3%,而对蔬菜产量没有显著影响。4)减少灌溉量15%和30%分别使总氮淋溶比常规水肥处理降低43.1%和50.5%,水氮协同调控对降低氮淋溶效果显著;对需水量较高的黄瓜季,灌溉量降低30%黄瓜产量显著降低13.9%。5)高量水肥投入条件下连续种植蔬菜3年6季后,0～80cm土壤剖面硝态氮积累量占0～200 cm土壤剖面积累量的38.2%～50.7%,土壤剖面积累了大量硝态氮而且向深层土壤中移动。因此,合理控制水肥管理,特别是减氮结合脲酶抑制剂和硝化抑制剂配合水分管理,是经济可行的有效阻控土壤氮淋溶的措施。