| Nansi Lake is the largest freshwater lake in North China, is also the necessary path of theeastern route of South-to-North Water Transfer project, and its water quality directly effectsthe success or failure of East Route Water Diversion project. Nansi Lake is a eutrophic lake,which is caused mainly by the inflowing water containing more nitrogen, phosphorus,suspended solids and other organic matter. Along with the progress of the South-to-NorthWater Diversion Project, remarkable achievements of controlling point source pollution arebeing made by shutting down a number of polluting enterprises. In recent years, with therapid development of livestock breeding and the increasing production of livestock andpoultry manure in Nansi Lake area, the livestock manure application in farmland is the maindisposal way and result in serious agricultural non-point source pollution. The effectivecontrolling of the nitrogen and phosphorus loss from organic fertilizer can control thepollution of agricultural non-point source, which is of great significance to protect waterquality and safety of South-to-North Water Diversion project. The research was conducted bythe combining methods including field runoff experiment, small watershed monitoring,simulated rainfall experiment and chemical analysis in the typical area of Nansi Lake coast.The effectives and the profit and loss of the organic fertilizer under the wheat-corn, corn-garlic two planting patterns and the effects of different types and application patterns on theloss of nitrogen and phosphorus were discussed in the paper to probe into the nutrientutilization efficient of organic fertilizer and the characteristics of farmland nitrogen andphosphorus loss and to value preliminarily the non-point source pollution by water qualitymonitoring of the small typically closed watersheds. The main conclusions are as follows:1. The in-season utilization efficiency of organic fertilizer was relatively lower, anddecreased with the increment in its dosage and affected by cultivation seasons. Morespecifically, under wheat-maize rotation, the apparent recovery efficiency of applied N and Pwere14.10%and6.03%in average after adding duck manure within wheat season,respectively, and they were9.25%and4.97%after incorporating cow dung. Undergarlic-maize rotation, they were9.17%and4.03%after treated by composted chicken manurewithin garlic season. Under wheat-maize rotation, the apparent recovery efficiency of appliedN and P were27.29%and15.99%, respectively, after applying duck manure within maizeseason, and they were17.58%and13.20%after the incorporation of cow manure. Whileunder garlic-maize rotation, they were26.40%and13.92%after adding composted chickenmanure within maize season.2. The digestion and sequestration of organic fertilizer by farmlands contributed to soil nutrient accumulation and the proportions of soil apparent accumulation of N and P fromorganic fertilizer in the applied dosage enhanced with increased application dosages, affectedby the types of organic fertilizer and application patterns. Specifically, under wheat-maizerotation, the proportions of soil apparent N and P accumulation in application rate were39.06%and63.59%, respectively, after adding cow manure, and were26.37%and60.49%treated by duck manure. Under garlic-maize rotation, they were33.52%and60.70%mixedwith composted chicken manure. Additionally, top application had higher proportions of soilapparent N and P accumulation in application rate than furrow application, indicating thecontribution of furrow application of organic fertilizers to the nutrient accumulation in soils.3. The digestion and sequestration of organic fertilizer by farmlands could also result innutrient loss, and the proportions of soil apparent loss of N and P from organic fertilizer in theapplied dosage increased with the increment in application dosages, influenced by the types oforganic fertilizer and application patterns. In details, under wheat-maize rotation, theproportions of soil apparent N and P loss in application rate were15.35%and13.84%,respectively, after adding cow manure, and were19.29%and18.07%treated by duck manure.Under garlic-maize rotation, they were16.32%and14.96%mixed with composted chickenmanure. Furrow application of cow dung had lower apparent loss of N and P than topapplication, indicating its improvement in nutrient loss.4. Total N (TN) concentration in surface runoff liquid and eroded sediment was affectedby the amount of fertiliser applied significantly, promoted with increased fertilisation dosage.More specifically, rainfall led to big increment in the TN of both surface runoff liquid anderoded sediment after topdressing of organic fertiliser in the short term, but exerted slightinfluence on TN in leachate. Also, total P (TP) had a similar change in surface runoff liquid,eroded sediment and leachate. Compared with topdressing, banding treatment had lower TNand TP in surface runoff liquid and eroded sediment, higher TN in leachate, similar TP afterapplying same amount of fertiliser under same rainfall condition. Additionally, treatment forcow manure had lower TN and TP in surface runoff liquid, leachate and eroded sediment thanthat for duck manure, but their differences were not significant.5. There were three pathways of TN loss, including surface runoff liquid (50.83%) whichwas dominated, leachate (35.37%) and erosion (13.8%). Sediment erosion was the major wayof TP loss, occupying49.90%, followed by surface runoff and leachate which were33.35%and16.75%, respectively.6. Among different fertilisation patterns, mixed application could lower N loss in anyforms under different rainfall intensities after adding same amount of fertiliser. And the decreases became greater with increased rainfall intensity. Specifically, TN, nitrate N,ammonium N, particulate N and water soluble organic N all reduced by120mm/h. Underhighest rainfall intensity, there were31.66%、24.94%、22.43%、24.49%、24.17%decrease,respectively. Conversely, the N loss of different forms in surface runoff all increased with theincrement in fertiliser levels under different rainfall intensities. The increases could reach to47.21%、61.93%、35.17%、56.93%、33.01%under highest rainfall intensity. There were notsignificant differences in amount of N of various forms among different rainfall intensities.Mixed application had smaller total variation of different N forms in the proportion of TNloss compared with topdressing under low fertiliser level, while had larger variation underhigher fertiliser level. The variation could reach-3.13%and2.58%, respectively. Thereinto,the variation of ammonium N in the proportion of TN all increased to a maximum of4.29%under different rainfall intensities. Under same fertiliser patterns, the variation of different Nforms in the proportion of TN loss varied with increased fertiliser level in which the variationof nitrate N in the proportion of TN all increased to a maximum of10.00%.7.Under same fertiliser level, mixed application could lower TP, water soluble inorganicP, water soluble organic P, water soluble TP and particulate P by35.79%、27.01%、33.95%、27.96%、39.08%, respectively, compared with topdressing. But they could be promoted by106.6%、47.87%、57.15%、48.82%、150.55%when the fertiliser level was doubled. Generally,mixed application had lager variation of different P forms in the proportion of TP thantopdressing under low fertiliser level, as much as25.91%larger in average. Under samefertilisation pattern, the variations of different P forms in the proportion of TP decreased, to56.87%in average, as fertiliser levels increased with the exception of particulate P whichincreased to21.06%in average.8. There were large correlation between water quality index and underlying surfaceelements. Different land use types exerted various influence on watershed non-point sourcepollution. More specifically, rural residential land had biggest influence, followed byfarmland, and forest land, Lake Surface had minor influence. The exportation of N and P fromclosed watershed in Nansihu region majorly resulted from plantation and domestic use, andtheir amount were1494.26kg and55.63kg, respectively. The runoff quality generated byrainfall reached mid-eutrophication level or eutrophication level. |
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