Effect of fertilization and irrigation schedule on water and fertilizer solute transport for wheat crop in a sub-humid sub-tropical region

In order to increase the water and fertilizer use efficiency and decrease the losses of water and fertilizer solutes (N and P), it is necessary to assess the influence of level of fertilization and irrigation schedule on movement and balance of water and fertilizers in the root zone. With this goal, the reported study was undertaken to determine the effect of fertilization and irrigation schedule on water movement and fertilizer solute transport in wheat crop field in a sub-tropical sub-humid region. Field experiments were conducted on wheat crop of cultivar Sonalika (Triticum aestivum L.) during the years 2002–2003, 2003–2004 and 2004–2005. Each experiment consisted of four fertilizer treatments and three irrigation treatments during the wheat growth period. During the experiment, the irrigation treatments were: I₁ = 10% maximum allowable depletion (MAD) of available soil water (ASW); I₂ = 40% MAD of ASW; I₃ = 60% MAD of ASW. The fertilizer treatments during the experiment were: F₁ = control treatment with N:P₂O₅:K₂O as 0:0:0 kg ha⁻¹; F₂ = fertilizer application of N:P₂O₅:K₂O as 80:40:40 kg ha⁻¹; F₃ = fertilizer application of N:P₂O₅:K₂O as 120:60:60 kg ha⁻¹ and F₄ = fertilizer application of N:P₂O₅:K₂O as 160:80:80 kg ha⁻¹. The results of the investigation revealed that low volume high frequency irrigation results in higher deep percolation losses than the low frequency high volume irrigation with different levels of fertilization for wheat crop in coarse lateritic soil, whereas different levels of fertilization did not significantly affect soil water balance of the wheat crop root zone during all the irrigation schedules. Level of fertilization and irrigation schedule had significant effect on nitrogen leaching loss whereas irrigation schedules had no significant effect on nitrogen uptake under different levels of fertilization. On the other hand, the leaching loss of phosphorus was not significantly influenced by the irrigation schedule and level of fertilization of wheat crop. This indicated that PO₄–P leaching loss was very low in the soil solution as compared to nitrogen due to fixation of phosphorus in soils. From the observed data of nitrogen and phosphorus use efficiency, it was revealed that irrigation schedule with 40% maximum allowable depletion of available soil water with F₂ fertilizer treatment (N:P₂O₅:K₂O as 80:40:40 kg ha⁻¹) was the threshold limit for wheat crop with respect to nitrogen and phosphorus use, crop yield and environmental pollution.     

再生回用水灌溉对作物品质及土壤质量的影响

考查了不同水质（三级处理水、二级处理水、污水、清水作对照）灌溉对农作物（黄瓜、白菜和玉米）品质和土壤质量的影响,同时测定了灌溉后农作物的可食用部分中的氯离子、磷酸盐、硝酸盐、亚硝酸盐以及残留的重金属含量.结果表明,三级水和二级水浇灌对作物品质无显著影响,污水浇灌可使部分营养成分含量升高,如以蛋白质为例,4种水浇灌时3种作物中蛋白质含量范围分别为：黄瓜0.736?2～0.812?5 mg/kg;白菜0.134?8～0.164?5 mg/kg;玉米10.28～10.84 mg/kg.污水浇灌会产生较高的硝酸盐积累,其中污水浇灌的白菜中硝酸盐含量高达554.4　mg/kg,已达到污染水平.三级水和二级水灌溉对作物中重金属含量影响不大,而污水浇灌会使作物中重金属发生明显的积累,因此污水不适于作灌溉水源.短期灌溉内土壤的钠吸附比(SAR)在3.5～4.5之间,表明土壤未发生明显碱化,重金属也未发生显著积累.     

Long-term impact of municipal sewage irrigation on treated soil and black locust trees in a semi-arid suburban area of Iran

The effects of municipal sewage irrigation on the soil and black locust (Robinia pseudoacacia L.) tree were studied. For this purpose, two artificial black locust stands under irrigation of municipal sewage and well water were selected in south of Tehran, Iran. Data were collected using technique of systematic random sampling with 4 replicates in each stand. It was found that the growth of black locust tree, as indicated by diameter at breast height, total height, crown length, average crown diameter, basal area and volume, in sewage irrigation stand was much higher than that of well water irrigation stand (P < 0.01). Plant analysis indicated that concentrations of leaf nutrients (N, P, K, Ca, Mg, Na, Fe, Mn, Cu and Zn) were greater in sewage-irrigated trees, without toxicity to the minerals of tree leaf, than those of well waterirrigated trees, and positively correlated with their respective value in soil. Ni, Cr and Pb were not detected in leaf samples. Application of sewage resulted in a 1.5-fold increase in the concentrations of soil nutrients, Ni, Cr and Pb. Among these minerals only Pb and Ni in some soil samples exceeded the toxicity limit. The increase in pH, electrical conductivity (EC) and organic carbon of soil was also observed in sewage irrigation. Results confirm that besides the use as irrigation water, municipal sewages are also a potential source of plant nutrients. However, significant accumulation of heavy metals such as Pb and Ni in soil needs to be monitored.     

粗放型绿色屋面填料的介质组成对出水水质的影响

通过模拟降雨实验监测填料组成不同的绿色屋面模拟设施出水水质,研究粗放型绿色屋面设施填料组成对出水污染物特征的影响.结果表明,设施出水中主要的污染物包括不同形态的N、P以及COD;除COD外,出水中污染物浓度随累积降雨量增加而下降,具有明显的淋失效应;所有设施出水中重金属含量均较低,初期出水的平均浓度均达到饮用水标准.含有田园土、醋糟的绿化种植土出水营养物质淋失严重,在累计降雨150 mm情况下,设施出水TN、TP、COD平均浓度分别为2.93、0.73和78 mg·L-1,均超过地表水水质标准Ⅴ类的限值,添加水厂污泥可以有效地减少绿化种植土中TP的淋出且不影响植物对P的吸收;使用无机复合种植土的设施出水水质较好,但仍需要结合设施对水量削减能力和植物生长状况判断填料是否能够应用于粗放型绿色屋面.     

华北平原农田硝态氮淋溶率和淋溶负荷估计

由于化肥过度施用且强度逐渐增加,华北平原氮淋溶问题日趋严重且造成了地下水污染风险.利用1991年以来公开发表的文献中290 组农田NO₃^--N 淋溶试验样本(淋溶率和10个影响因素),基于Bayesian递归回归树模型初步建立了华北平原农田NO₃^--N淋溶迁移过程统计模型.以2008年为例,基于华北平原县域合成氮肥、复合肥施用量和1 km×1 km的影响因素和土地利用(耕地)数据,最终得到1 km×1 km的华北平原农田NO₃^--N淋溶率和淋溶负荷及其不确定性水平.初步结果表明:①模型校准和验证R²分别达到0.832和0.829,模拟结果相对可靠;②华北平原耕地NO₃^--N的淋溶率具有显著的空间分异,其中位值为15.4%(R₅₀为12.6%~18.2%),其主要影响因素为土壤TN量、施N量、灌溉比例与降雨量的比值等;相应地,2008年淋溶负荷和淋溶量分别为995.1 Gg·a^-1(833.4~1156.7 Gg·a^-1);③NO₃^--N淋溶率较高的区域集中在太行山脉以东、黄河附近以及苏北的县(区、市),淋溶负荷贡献最大为河南(~37.7%)、江苏(~24.8%)和河北(~21.6%).     

Nitrogen leaching under corn cultivation stabilized after four years application of pig manure to red soil in subtropical China

The impact of long-term pig manure application to a red soil in subtropical China on nitrate leaching was investigated in a field lysimeter experiment from 2002 to 2009. Simultaneously, nitrate leaching was simulated by water and nitrogen management model (WNMM) basing on these observed data to determine the environmental threshold of manure application. Nitrate concentrations in the drainage and nitrate leaching under low manure application (150 kg N ha⁻¹ y⁻¹) did not increase during the study period. Interestingly, the nitrate concentrations in drainage water following high manure application (600 kg N ha⁻¹ y⁻¹) increased exponentially in the first four years and then remained at 13 mg l⁻¹ for the next four years. Addition of lime based on high manure application had no significant effect on nitrate concentrations or total nitrate leaching. WNMM simulated the variation in corn yields and nitrate leaching well. The environmentally safe threshold for long-term application of pig manure was 360 kg N ha⁻¹.     

乌梁素海硝酸盐来源的季节性变化

乌梁素海是典型农业灌区退水型湖泊,其水生态环境保护对黄河流域生态保护具有重要意义.该研究通过开展乌梁素海流域农业排干和湖体硝酸盐的δ15N和δ18O分析,应用IsoSource同位素模型估算流域生产生活污水、土壤氮源、化肥和大气沉降的贡献率.结果表明:①湖区δ15N-NO₃-和δ18O-NO₃-值范围分别为-2.50‰~18.17‰和-12.02‰~45.09‰,其中夏秋两季δ15N-NO₃-值偏正,冬季偏负,且秋季δ18O-NO₃-值偏正.②春季湖水硝酸盐主要源于化肥和土壤氮源相关的农业活动,其贡献率为43.7%;夏季、秋季和冬季主要源于生产生活污水,贡献率分别为51.3%、38.8%和40.2%,其中夏季农业活动贡献率超过40%,大气沉降主要体现在秋季湖水中.研究显示:春季湖区硝酸盐来源主要集中于七排干和八排干的受水区域,以上区域应在春季着重加强农业面源污染控制;夏季和秋季湖区硝酸盐来源主要集中于五排干和七排干所处城乡区域,以上区域应强化城乡生活污水处理.      

Growth and value of Chlorella salina grown on highly saline sewage effluent

Chlorella salina was successfully cultivated in secondarily treated domestic sewage effluent of salinity (14%) in an outdoor cultivation tank. Removal efficiencies of NH₄⁺ -N, NO₃⁻ -N, and PO₄³⁻ -P by this alga from secondarily treated sewage effluent were 89–100%, 35–66% and 100%, respectively. The high removal efficiencies of inorganic N and P means that this process can be used as a tertiary sewage treatment. The yield of the sewage-grown algae was 5.1 g m⁻² day⁻¹ for a retention time of 6 days. The high protein content (46.8%), relatively good amino-acid profile and low metal content enabled the use of algal biomass as feed supplement for the silver carp (Hypophthalmichthys molitrix). The food conversion ratios (FCR) of 5% and 10% sewage-grown algae supplemented fish food were better than on the control diet (i.e. artificial fish food alone), while the FCR of 20% sewage-grown algae supplemented fish food and live sewage-grown algae alone were inferior to that on the control diet. These results indicate that cultivation of C. salina in secondarily treated sewage effluent of high salinity can be used as a tertiary sewage treatment to remove inorganic N and P from secondarily treated sewage effluent to reduce pollution problems, and to produce algal protein suitable as a supplement for fish feed in aquaculture.     

长期污水灌溉后林地土壤中磷的含量与移动

为尽可能地削减污水携带的N、P进入湖泊,处理后的城市生活污水被直接喷灌到新西兰罗托鲁阿市的Whakarewarewa森林,并建立了污水灌溉林地处理系统的长期定位试验地以评价生态系统对污水携带营养物质的同化能力.为查清长期污水灌溉土壤中P的数量、迁移淋失及其环境危机,对11a污水灌溉后火山灰土壤中磷的积累、再分布进行剖面分层采样测定.结果表明,土壤pH、TP、Olsen P、M3P、M3Ca和M3Mg在所有灌溉处理区的表层土壤(0～10 cm)均有显著(p0.05)增加,部分增加的显著性达到20～40 cm土层或更深层次土壤.大多数随灌溉而进入土壤的P被保存在上层土壤(0～40 cm)中.土壤Olsen P和M3P的浓度在中、高水平处理区的20 cm以上土层中超过了环境临界值(Olsen P为60 mg.kg-1;M3P为150mg.kg-1),磷饱和率(M3PSR)数值同时显示表层土壤对P的吸持已近饱和,预示土壤磷素有随下渗水向下移动的潜在可能.常规土壤采样以60 mg.kg-1 Olsen P测定值为环境临界值,可解决土壤剖面中磷的下移监测难题.以M3P与M3Al、M3Fe的摩尔比计算的磷饱和率(M3PSR)作为长期污水灌溉林地处理系统中土壤磷向下移动的环境危机临界值参数指标已不是很理想,对新的磷饱和参数的研究是今后的主要工作之一.     

Treated wastewater irrigation effect on soil, crop and environment： Wastewater recycling in the loess area of China

A study was carried out at the Loess Plateau in Dongzhi,China,to test the feasibility of using secondary treatment sewage effluent and to determine whether the water quality would then meet the recommended irrigation norm.Seven crops,including celery,wheat, maize,millet,apples,rapeseed and yellow beans,were tested in the study.Physical and chemical properties of the soil,crop yield and quality and leachate at different soil depths were measured.In most cases,the quality of the crops that made use of treated sewage was not distinctively different from those that did not use treated sewage.However,yields for the former were much higher than they were for the latter.Leachates at different soil depths were analyzed and the results did not show alarming levels of constituents.For a period of approximately 14 months,the treated sewage irrigation had no significant effect on the loess soil and no cases of illness resulting from contact with the treated sewage were reported.With treated sewage irrigation,a slight increase in the organic content of the soil was observed.     

北方典型灌区不同灌期农田系统中氮素迁移特征分析

以内蒙古河套灌区杭锦后旗解放闸灌域为研究区,分析2009年夏灌和秋浇前后土壤中、浅层地下水和土壤渗滤液中的硝态氮、总氮的分布特征,研究不同灌期农田系统中氮素的迁移规律及其影响因素.结果表明:夏灌对氮素的稀释作用明显,反硝化作用也会降低地下水中硝态氮的浓度,此外玉米地块的氮流失在夏灌时相对明显;秋浇是农田氮素淋失的主要阶段,一方面是硝态氮 (NO3-N) 在灌水作用下向下淋失,另一方面是土壤中的NO3-N 在反硝化作用下转变成N2O、N2和O2释放;夏灌与秋浇两次灌水前后地下水中总氮 (TN) 的峰值滞后于NO3-N,表明氮素的流失除以NO3-N的形式发生之外,部分氨氮以及有机氮等其他形式的氮素在灌溉驱动下也发生一定程度的纵向流失.     

市政污泥堆肥对矿山废弃地生态恢复影响的研究进展

市政污泥作为城市污水处理过程中的副产物,含有大量的有机质和丰富的氮、磷、钾等营养物质,经堆肥处理后可用作矿山废弃地生态恢复的土壤改良基质.已有实验室模拟和场地规模研究结果表明,污泥堆肥的施用可同步实现矿山废弃地土壤基本理化性质改善、土壤微生物数量和代谢活性提高、植被的快速生长和生态功能的快速重建.污泥堆肥所含的氮、磷、有机质和重金属,在降雨渗流、微生物和植物根系的共同作用下淋溶进入水体或被植物富集,已有淋滤柱试验和短期植物种植研究结果表明,矿山有短期的二次污染风险,但风险可控.国外污泥/污泥堆肥用于矿山生态修复的案例证明,市政污泥经稳定化处理可促进矿山生态恢复,形成有效碳汇,而长期生态影响未来需要开展不同地域的场地跟踪监测并进行系统定量评估,从而进一步探讨该技术路线的可行性和安全性,同步实现市政污泥处理处置和矿山废弃地生态修复的双重目标,这也将成为未来评估市政污泥堆肥用于矿山生态恢复可行性的重要研究方向.      

不同灌溉方式旱田土壤N2O排放和氮素淋溶特征

通过野外原位监测试验,利用静态箱-气相色谱法、土壤溶液提取器分别对旱田土壤N₂O排放及氮素淋溶进行2018和2019年连续两年观测.试验设计为DCK （滴灌无肥）、DD （滴灌+N 500kg/hm²）、DG （滴灌+N 1000kg/hm²）、FCK （沟灌无肥）、FD （沟灌+N 500kg/hm²）、FG （沟灌+N 1000kg/hm²）.结果表明,不同施氮量、不同灌溉方式对N₂O排放和氮素淋溶量影响具有极显著差异（P<0.01）.N₂O排放量随施氮量的增加而增加,滴灌与沟灌相比可有效降低N₂O排放,2018和2019年FCK、FD、FG的N₂O累积排放量分别为2,23.79,45.73kg/hm²和2.08,6.23,13.93kg/hm²,而DCK、DD、DG分别降低了35%、80.9%、75.6%和26.7%、66.4%、21.5%.2018和2019年旱田土壤氮素淋溶量均表现为：滴灌<沟灌,80cm深度土壤溶液氮素淋溶量<40cm.2018和2019年相同施氮量下滴灌与沟灌相比,在40cm和80cm分别能减少氮素淋溶量36.95%~63.10%和54.93%~87.92%.主成分分析结果表明,影响N₂O排放的主要环境因子为土壤NO₃^--N含量和降水频率,相关系数分别为0.689、0.596;影响氮素淋溶量的主要环境因子为降水频率和灌水频率,相关系数分别为0.697和-0.729.滴灌可有效减少N₂O排放和氮素淋溶量,在提高肥料利用率的同时可减轻环境污染.     

基于氮氧同位素技术的黄河上游清水河硝酸盐来源解析

对清水河灌溉季和非灌溉季各采样点位的水化学指标和硝酸盐的时空分布特征进行分析,运用贝叶斯混合模型MixSIAR模型定量识别了该河流硝酸盐来源,以期了解灌溉对地表水硝酸盐含量的影响.结果表明,清水河水体呈弱碱性,水体氮类以硝酸盐为主,Cl^-和SO₄^2-时空变化特征一致,通过NO₃^-/Cl^-比值和Cl^-浓度的关系,结合清水河地区土地利用、工农业生产的实际情况,揭示了清水河水体硝酸盐受生活污水、畜禽养殖和化学氮肥源的影响较大.MixSIAR模型计算结果表明土壤有机氮、化学氮肥和畜禽养殖对灌溉季水体的贡献率较大,分别为24.8%、24.5%和22.8%,生活污水和大气氮沉降的贡献率分别为14.4%和13.6%;而生活污水、畜禽养殖和土壤有机氮对非灌溉季水体的贡献率较大,分别为26.7%、23.4%和20.4%,大气氮沉降和化学氮肥贡献率分别为16.5%和12.9%.农业灌溉增加了地表水硝酸盐的含量,灌溉季中农用氮肥的施用率较高,贡献了主要的硝酸盐;非灌溉季生活污水的贡献率较高.     

雄安新区唐河污水库残留污染物对地下水水化学动态的作用机制

唐河污水库位于雄安新区白洋淀西侧,污水库渗漏和污水灌溉历时长达40 a,包气带中累积大量污染物.识别污水渗漏和灌溉复合系统残留污染物对地下水水化学动态的作用机制,对雄安新区的水环境保护至关重要.利用水化学离子示踪及改进的氯碱指数等水文地球化学方法,解析浅层地下水水化学时空特征及演化机制.结果表明,污水库区地下水水化学类型为SO₄ ·HCO₃-Na型,平均污水混合比例为48.4%,阳离子交替吸附作用和岩盐溶解作用分别为地下水提供了29.9%和8.6%的钠离子;污灌区地下水水化学类型为SO₄ ·HCO₃-Na ·Mg型,平均污水混合比例为58.3%,阳离子交替吸附作用降低了地下水中8.1%的钠离子;降水和灌溉水的混合稀释作用导致残留污水混合比例和矿物饱和指数降低,促进地下水中钠离子与土壤胶体吸附的钙镁离子的交换作用.含水层反硝化作用能有效减少地下水硝酸盐污染.此外,污水库修复前后污水比例分别为61.5%和49.3%.污水渗漏和灌溉复合系统中长期滞留的污染物将在降雨和灌溉模式驱动下以不同程度的污水物理混合和水岩相互作用持续影响浅层地下水水质.     

不同施氮水平对再生水灌溉土壤释氮节律的影响

土壤供氮能力是影响土壤氮素利用效率的一个重要指标,再生水灌溉和施氮水平均影响着土壤供氮能力,研究不同施氮水平对长期再生水灌溉土壤氮素的转化特征可为合理施肥及农产品增产增效提供理论依据.本研究选择河南新乡洪门试验站温室大棚内长期再生水灌溉和清水灌溉土壤,试验共设8个处理:A(N200)(施氮量200 mg·kg-1)、A(N160)(施氮量160 mg·kg-1)、A(N140)(施氮量140 mg·kg-1)、A(N100)(施氮量100 mg·kg-1)、A(N0)(施氮量0 mg·kg-1)、E(清水灌溉常规施氮)、CK(清水灌溉不施氮)、Re CK(再生水灌溉不施氮),采用实验室内常温培养法,分别在培养的7、14、21、28、35、42 d测定土壤铵态氮、硝态氮及全氮含量,并分析了土壤氮素矿化量和氮素矿化速率的变化,通过Freundlich线性等温吸附模型及一级动力学方程拟合了土壤吸附参数Kd和氮素矿化势N0.结果发现,培养前期土壤氮素矿化较快,释放的氮量较高,中后期变化较慢,土壤供氮平稳,同一时段不同处理间土壤累积矿化氮量存在显著差异(p0.05),表明不同外源氮肥输入对土壤氮素的矿化能力影响显著,A(N160)处理的供氮能力最强;同时,在培养前期Re CK处理的土壤氮素矿化累积量显著高于CK处理,表明再生水灌溉较清水灌溉促进了土壤氮素的矿化,显著提高了土壤氮素活性;土壤氮素的矿化速率随着培养时间的增加而逐渐降低,但降幅依次减小并趋于平稳,且不同施氮处理再生水灌溉土壤氮素矿化速率显著高于清水灌溉;不同土壤肥力水平(B0)、外源施氮A(N160)调控,土壤氮素矿化潜势可表达为N0=B0+117.5072t-0.1062.因此,外源氮肥输入显著影响了土壤氮素释放节律,再生水灌溉辅以适宜的施氮量可促进土壤氮素矿化,提高土壤氮素活性.     

Differential N uptake by maize cultivars and soil nitrate dynamics under N fertilization in West Africa

Nitrate is prone to leaching in the sandy soils of the West African moist savannas. Better management of nitrogen (N) resources and maize cultivars with enhanced genetic capacity to capture and utilize soil and fertilizer N are strategies that could improve N-use efficiency. In two field experiments conducted at Zaria, northern Nigeria, five maize (Zea mays L.) cultivars planted early in the season were assessed under various N levels for differences in N uptake, soil N dynamics, and related N losses. Cultivar TZB-SR accumulated more N in the aboveground plant parts in both years than the other cultivars. All, except the semi-prolific late (SPL) variety, met about 50–60% of their N demand by the time of silking (64–69 DAP). In both years, SPL had the greatest capacity to take up N during the grain filling period, and it had the highest grain-N concentration and the least apparent N loss through leaching in the second year. There were no significant differences in soil N dynamics among cultivars in both years. At harvest, the residual N in the upper 90 cm of the profile under all the cultivars ranged from 56 to 72 kg ha⁻¹ in the first year and from 73 to 83 kg ha⁻¹ in the second year. Apparent N loss from 0 to 90 cm soil profile through leaching ranged from 35 to 122 kg ha⁻¹ in both years. N application significantly increased N uptake by more than 30% at all sampling dates in the second year of the experiment, but had no effect on apparent N loss. Results indicate that the use of maize cultivars with high N uptake capacity during the grain filling period when maximum leaching losses occur could enhance N recovery and may be effective in reducing leaching losses of mineral N in the moist savanna soils.     

焦作市某污灌区地下水无机氯化物污染原因初探

通过对研究区河流、土壤等环境因素的分析调查,并对污灌区土柱的淋溶和静溶试验,分析了土柱溶液的产生过程,同时分析了污水灌溉与该区地下水中氯离子浓度升高的关系,得出污水灌溉是造成污灌区地下水无机氯化物污染的重要原因,并由此提出了一些应对措施。     

基于RZWQM模型模拟太行山低山丘陵区农田土壤硝态氮迁移及淋溶规律

太行山低山丘陵区是华北平原地下水补给区,近年来山区农田面积增加,农田过量氮肥投入造成地下水硝酸盐浓度逐年升高,因此,研究典型农田土壤氮淋溶过程对保护补给区地下水具有重要意义.本文以位于太行山低山丘陵区的中国科学院太行山生态试验站冬小麦-夏玉米轮作农田为研究对象,应用根区水质模型（root zone water quality model,RZWQM）对太行山低山丘陵区2015~2016年冬小麦-夏玉米的1个轮作周期内1m土壤剖面水分和硝态氮运移进行模拟.结果表明,土壤硝态氮淋溶主要发生在夏玉米季（雨季）,当全年施氮量为300 kg·hm^-2时,夏玉米季硝态氮淋失量达到59.9 kg·hm^-2,而冬小麦生长季硝态氮淋失量仅为2.12 kg·hm^-2.不同施氮量和不同降水年型下玉米季土壤硝态氮淋溶模拟结果表明,当施氮量为0、300和450 kg·hm^-2时,2016年（丰水年）极端降水后,玉米季土壤硝态氮潜在淋失量分别为10.5、59.9和136.5 kg·hm^-2;当全年施氮量为300 kg·hm^-2时,2013（枯水年）、2015（平水年）和2016年（丰水年）玉米季硝态氮淋失量分别占轮作周期总施氮量的9%、10%和20%;当全年施氮量为450 kg·hm^-2时,2013（枯水年）、2015（平水年）和2016年（丰水年）玉米季硝态氮淋失量分别占总施氮量的11%、17%和30%,表明大降水事件不仅对地下水形成大量补给,很大程度上也增加了累积在农田土壤中的硝态氮淋溶损失,增加了对区域地下水硝酸盐潜在污染威胁.     

Nitrates leaching from agricultural land in Hamadan, western Iran

Nitrogen (N) is vital for plant and microbial growth and rather large amounts are required by most arable and horticulture plants. High nitrate (NO₃⁻) levels of water supplies have been attributed to leaching from the soil and into water systems. In the arid and semi-arid regions, irrigation water carries NO₃⁻ into groundwater. This study was conducted to investigate NO₃⁻ pollution of groundwater in Hamadan, western Iran. The water samples were mostly taken from domestic and community wells. In this area, the drinking water supply comes mainly from groundwater sources. Nitrate concentrations in the well samples varied from 3 to 252 with the average of 49 mg l⁻¹. Results showed that of 311 wells, 196 (63%) had levels less than 50 mg l⁻¹ and 115 (37%) had levels in excess of the 50 mg l⁻¹ NO₃⁻. Agriculture is the dominant land use in the area and application of N fertilizers clearly has an impact on groundwater. If agricultural losses remain stable, it could be expected that the concentration of NO₃⁻ in groundwater will reach or exceed the international recommendations for drinking water (50 mg l⁻¹) in the future. Irrigation with high NO₃⁻ groundwater can minimise the requirement for N fertilizers. To maintain yield increase and minimise NO₃⁻ pollution of the groundwater, best management practices, for N fertilizer use should be applied and excessive fertilizer application prevented.