Study On Dynamic Changes Of Soil Inorganic Phosphorus And Their Migration Characteristics Of The Farmland In The Three Gorges Reservoir Area,China

Population surplus, shortage of resources and deterioration of environment are the three obstacles which restrict the development of China’s society, economy and people’s living standard. Currently, the world is facing the challenges of maintaining food production growth and the improvement of agricultural ecological environmental quality. The Eighteenth National Congress of the CPC has put the ecological civilization construction and the economic, political, social and cultural construction in the equally important position, the agricultural non-point source pollution governance has attracted great importance to good agricultural non-point source pollution control. Phosphorus is one of the agricultural production in the most important nutrient limiting factor, however, the excessive application has caused serious eutrophication problems. A large number of studies have also shown that, phosphorus, which is a key element, is one of the main elements to result in agricultural non-point source pollution. So the establishment of both soil phosphorus with high crop yield and environmental protection in the appropriate phosphorus fertilization recommendation system has important significance for agricultural production and water environmental protection.The soil phosphating, exchange and transfer between typical soil-water-atmosphere interfaces, and agricultural non-point source pollution has an obvious geographical and systematic characteristics. Purple soil is mainly distributed in the upper reaches of Yangtze River, consists of 78.7% of the cultivated area in the Three Gorges Reservoir area. With the increase of land use intensity, soil erosion is becoming increasingly serious, resulting in the loss of soil nutrients and eutrophication pollution, exacerbated the deterioration of the ecological environment. Therefore, the intensity of flux and temporal variation of soil phosphorus decreased in specific region. By applying science and technology,improving the fertilizer management as well as the organic agriculture and strengthening the typical circulation, in situ proven purification ecological and interception of phosphorus, the output of phosphorus in soil nutrient has been further reduced. The Comprehensive emission reduction is a new trend of soil phosphorus in agricultural non-point source pollution mechanism and control technology research and development, mainly in the process of soil micro ecology to loss of phosphorus pollution. It can also optimize chemical fertilizer,organic fertilizer and their ratio and reduce the amount of phosphorus pollutants that are released to soil and water.This study combined with the current ―control and reduction‖ strategy, we pay attention to the optimization of chemical fertilizer reduction and organic and inorganic fertilizer combined application and find out the condition of chemical fertilizer and organic fertilizer in purple soil, soil phosphorus element loss source intensity and runoff and leaching characteristics for a comprehensive understanding of purple soil agricultural phosphorus element loss and effective evaluation of phosphorus loss. In this paper, we took the main purple soil of our farmland in Three Gorges area as materials, by the 22 years long-term field experiment and field observation method with laboratory analyse, to get the temporal and spatial scales of the long-term variation characteristics of soil profiles of inorganic phosphorus in purple soil under the application of inorganic fertilizer, the evolution of phosphorus and long-term conservation tillage system. The winter wheat and summer maize rotation system was used to study the migration and transformation characteristics and controlling factors. Meanwhile, the rice-rape cropping system in puple soil was also used to study the phosphorus characteristics in both soil and water systems. In doing so, we aimed to establish the soil-water-planting coupling of purple soil agricultural phosphorus element migration loss model, for the prediction of soil phosphorus loss amounts in the Three Gorges Reservoir to develop reasonable fertilization and tillage measure. The main results were as follows:1.Taking the Jiang Bofan-Gu Yichu Inorganic phosphorus Grading System to conduct grading measurement on the morphology of inorganic phosphorus of the 0-100 cm purple soil layer in the 22-year long-term fertilization experiment. The results showed that, compared to the status before the experiment, the total phosphorus, available phosphorus and various forms of inorganic phosphorus had all increased to a certain degree in the soils with long-term application of chemical phosphate and the combination of organic fertilizer and chemical fertilize. Among these fertilizations, the pig manure+NPK(M+NPK) had increased the content of available phosphorus by six times; while the available phosphorus, total phosphorus, and various forms of inorganic phosphorus had reduced in the soil without fertilization(CK) and the sole nitrogenous fertilizer(N). In particular, the contents of available phosphorus had reduced by 51.1% and 53.5% under CK and N, respectively. In addition, the contents of Fe-P and Ca10-P in the lower layer were higher than those in the upper layer, all other forms of inorganic phosphorus were higher in the arable layers than in the lower layers. The distributions of inorganic phosphorus like Ca2-P, Al-P, Ca8-P, and O-P in the soil profile were all similar to each other, and all had reduced quickly at 20-60 cm, but were similar or had a slightly increase trend at 80-100 cm. In addition, the phenomenon of the content of Fe-P in lower layer higher than that in the arable layer. It had been shown by relevant analysis that the contribution of various groups of inorganic phosphorus to purple soil was Ca2-P(0.9569) > Al-P(0.9265) > Ca8-P(0.9100) >Fe-P(0.8277) >Ca10-P(0.7449) >O-P(0.7362). Long-term of combined application of organic and inorganic fertilizers could significantly increase the accumulation of phosphorus in soil, suppress the decreasing of P fixation, enhance P mobility and P use efficiency.2. In this study the effects of tillage methods(rice-winter paddy field conventional farming, CF; rice-winter paddy field combing ridge with no-tillage, RNT1; rice-wheat or rape combing ridge with no-tillage, RNT2; rice-wheat or rape conventional paddy-upland rotation tillage, CR) on purple soil profile of different forms of inorganic phosphorus distribution were investigated in a long-term experimental site established in 1990, Chongqing City, China. The results had shown that, compared to the status before the experiment, the total phosphorus, available phosphorus and various morphologies of inorganic phosphorus had all increased to a certain degree in the soils with long-term different tillage treatment, and the different forms of inorganic phosphorus content in soil size order is RNT2>CF>CR>RNT1. In addition to that the contents of Fe-P in the lower layer were higher than those in the upper layer, all other various morphologies of inorganic phosphorus had all characterized as that the arable layers were higher than the lower layers. The effects of farming practices on availability of various phosphorus farms were significant. They were in the order of CR>RNT>CF. Long-term of conventional paddy-upland rotation tillage was more advantageous to crops on the absorption of phosphorus. From the different inorganic phosphorus in different purple soil profiles in the proportion of total inorganic phosphorus, Ca10-P and O-P were higher, so calcium and phosphate took the largest proportion of all.3. In different fertilization conditions, the characteristics of the annual runoff of the soil under drought sloping field could be seen that the loss of total phosphorus(TP) and total soluble phosphorus(TDP) were significantly different under different fertilization treatments. Each treatment TP and TDP change range was large, 0.06~1.58 kg·hm-2·a-1 and 0.009~0.268 kg·hm-2·a-1, respectively. From 2011-2014 different fertilization treatments of TP and TDP average total loss could be seen, TP loss size followed by times the amount of applied fertilizer(2P) >optimum fertilization(P) >optimization fertilization + pig manure organic fertilizer(MP) >optimization fertilizer + straw(SP) >optimum amount of fertilizer phosphorus minus 20% pig manure organic fertilizer(MDP) >optimization of fertilizer phosphorus reduced 20% straw(SDP) >No application of phosphate fertilizer(P0). Optimization of fertilization(P) were about 1.5 to 2 times the optimum amount of fertilizer phosphorus reduction + straw(SDP) processing and optimization of fertilizer phosphorus minus 20% pig manure as an organic fertilizer(MDP).TDP loss of TP loss and the quantity of the order of magnitude was slightly different, the size followed by times the amount of applied fertilizer(2P) >optimization fertilization + pig manure organic fertilizer(MP) >optimization fertilization(P) >optimum amount of fertilizer phosphorus minus 20% pig manure organic fertilizer(MDP) >optimization(SP) fertilizer + straw >optimum amount of fertilizer phosphorus reduced 20% straw(SDP) >Application of phosphate fertilizer(P0). The fertilizing phosphorus element loss and rainfall amount correlation analysis showed that, the total phosphorus accumulation loss and rainfall accumulation were y(28)a Ln(x)-b, a(29)0(R2=0.8306~0.9473) logarithmic relationship related, the total soluble phosphorus accumulation loss and rainfall accumulation were y(28)ax(10)b, a(29)0(R2=0.9302~0.9803)(the P0 is a logarithmic relationship relation). In order to better understand the effect of reduced phosphorus fertilizer and combining organic fertilizers on phosphorus loss of purple soil sloping field, three rainfall-runoff events were monitored by using field runoff observation method in the purple soil sloping field in 2014. There were six treatments in this research, including optimized fertilization(P), optimized fertilization +pig manure application(MP), optimized fertilization +straw return(SP), optimized fertilization which was reduced by 20% +pig manure application(MDP), optimized fertilization which was reduced by 20% + straw return(SDP), without phosphate(P0).The results indicated that the interflow was the main pathway of runoff for purple soil sloping field. The average contents of total phosphorus(TP) and the phosphorus loss load of overland flow were all much higher than the interflow. The overland flow was the main pathway of the phosphorus loss load for purple soil sloping field. Reduced phosphorus fertilizer and combining organic fertilizers had a significant reduction effect on phosphorus loss of purple soil sloping field. Compared with the treatment P, the average contents of total phosphorus on SDP was reduced by 57% and on MDP was reduced by 48% in the storm rainfall. Combining straw was better than pig manure. The average contents of the phosphorus loss load of typical rainfall were changed from 0.01 to 0.47 kg·hm-2. In different fertilization treatments, the average contents of the phosphorus loss load listed as follow: P>MP>SP>MDP>SDP>P0. Reduced phosphorus fertilizer and combining organic fertilizers had a significant reduction effect on phosphorus loss of overland flow, but increased soil phosphorus leaching for purple soil sloping field. Therefore, to control the phosphorus loss first to control soil erosion, fertilizer and organic fertilizer on the balance of the thick soil layer should be taken to enhance the comprehensive governance, soil organic matter and other measures. The influence on different fertilization treatments on winter wheat-summer maize growth and development showed that, the winter wheat season and summer maize season of all double the amount of phosphorus fertilizer(2P) were the highest, but phosphorus element on utilization rate was not high. Winter wheat optimal phosphorus fertilizer + straw(SDP) and optimum amount of fertilizer phosphorus reduction 20%+pig manure organic fertilizer(MDP), the utilization rate of which respectively was 4.2% and 5.9% higher compared with the conventional optimal fertilizer(P) treatment of phosphate fertilizer. The apparent utilization rate of fertilizer application in maize season was also significantly higher than that of single fertilizer application(P<0.05). While the amount of phosphorus absorbed by the crop could be increased by the amount of(2P), the economic benefit and utilization rate was greatly reduced, which led to the waste of fertilizer resources and environmental pollution. The application of organic and inorganic fertilizer could significantly increase the absorption and utilization of phosphorus fertilizer in crops. The appropriate reduction of phosphorus and organic fertilizer could improve the rate of phosphorus fertilizer in the winter wheat and summer maize under the condition of no reduction of yield in purple soil.4. The effect of the results on optimization and reducing phosphorus with organic fertilizer on rice, growth development and phosphate fertilizer use rates showed that application, in conventional crop fertilization based on reducing the chemical fertilizer application amount, and combined application of organic fertilizer, on crop yield did not show significant reduction, and in some extent it could reduce agricultural phosphorus loss to improve phosphorus utilization. The utilization of phosphate fertilizer in rice rate overall showed that: optimization of fertilizer phosphorus minus 20% pig manure organic fertilizer(MDP)>optimization of fertilizer phosphorus reduction + straw(SDP)>optimization fertilizer and hog manure organic fertilizer(MP)>optimize fertilizer + straw(SP)≈optimal fertilizer(P), the treatment of phosphate fertilizer and using rate between 20% to 25%. Rape of phosphate fertilizer utilization rate of overall performance: the optimizing fertilization and phosphorus reduction 20%+straw(SDP)>optimum amount of fertilizer phosphorus reduced 20%+pig manure organic fertilizer(MDP)>optimize fertilizer +hog manure organic fertilizer(MP)>optimization fertilizer + straw(SP)>optimal fertilizer(P), the treatment of phosphate fertilizer using rate were between 17%~29%. Different growth periods of oilseed rape in the soil phosphorus element dynamic results showed that bud stage soil available phosphorus seedling significantly reduced, but in rape flowering stage and harvesting stage, soil available phosphorus had an obvious rise, it was the main period of soil available phosphorus leaching after the rape growth period. Different fertilization treatments on paddy field surface water TP content dynamic change research showed that, in the rice growth within a month, field surface water total phosphorus content increased with the increase of the levels of phosphorus fertilizer, optimized fertilization(P) than no P fertilizer(P0) treatment and phosphorus content was about 4 times higher. The phosphorus content of the size performance for optimal fertilization(P) >optimization fertilization + pig manure organic fertilizer(MP) >optimization fertilizer + straw(SP) >optimum amount of fertilizer phosphorus minus 20%+ pig manure organic fertilizer(MDP) >optimization of fertilizer phosphorus reduced 20%+ straw(SDP) >Application of phosphate fertilizer(P0) after a month of different fertilization treatment field surface water total phosphorus content was basically the same, 80 days after the treatment of total phosphorus content close to no phosphorus treatments. The critical period of field control of phosphorus loss was after P put into the field in 7-10 days, during the period of any rainfall runoff or human disturbance and farmland drainage might make a lot of phosphorus loss in water environment, which could increase the risk of water pollution. In order to explore the effective tillage for reducing phosphorus leaching and improving river water quality,field experiments were conducted to study the effect of combined application of organic and inorganic fertilizers on phosphorus leaching in purple paddy soil of conventional paddy-upland rotation tillage. The results showed that the phosphorus seepage decreased over time, but the amount leached was high and variable at the earlier stages, gradually stable equilibrium after 55 days. The TDP was the dominant one in the P leaching water of the purple paddy soil. The soluble phosphorus and total phosphorus content in soil leachate listed as follow: optimized fertilization +pig manure application(MP)>optimized fertilization +straw return(SP)> optimized fertilization>optimized fertilization which was P reduced by 20% +pig manure application(MDP)>optimized fertilization which was P reduced by 20% + straw return(SDP)>without phosphate(P0). The change of TP loss load was between 0.295 and 0.493 kg·hm-2. Organic fertilizer promoted the phosphorus leaching, and the pig manure promoting effect was bigger than the rice straw. From the experiment research we ccould see different fertilization treatments on crop growth, phosphate fertilizer use rate and on soil phosphorus element effective and phosphorus element leaching risk to water environment, we could also draw the conclusion that chemical fertilizer reduction and straw with fertilizer were dealt with the agricultural non-point source pollution measures to ―control the sources and the runoff loss ". To improve the agricultural production and control the non-point source pollution, we could reduce the chemical fertilizers and then combine organic and inorganic fertilizers application.5. The water- soil- planting fields in purple soil dynamic loss model could be better to quantify the simulation and prediction of reactive phosphorus(MRP) content variation and characteristics of phosphorus transport and loss in purple soil sloping land in the Three Gorges reservoir area in surface water. Fixed rate constants was the most sensitive, and had maximum effect to the results. Drainage in the early stages of fertilization could lead to phosphorus with drainage losses increase. Therefore, a reasonable irrigation in paddy field had its positive significance to control phosphorus element loss.From 22 years long-term fertilization experiment and long-term farming system of purple soil in the test site and undisturbed soil seepage pool, with the time and space scales, taking into account the paddy field, dry land soil, we systematically studied the phosphorus migration transformation characteristics in purple soil in the Three Gorges area, and received a large number of basic monitoring data and research results, which could provide theoretical basis for purple soil cropland phosphorus optimized management and implementation of reasonable fertilization and tillage system. And to study the effects of different phosphorus levels and different kinds of organic fertilizer on phosphorus migration in purple soil, it was a good measure if the optimum amount of fertilizer phosphorus could be reduced by 20% with the application of straw manure to control the soil phosphorus element loss in purple soil.