Study On Distribution And Circulation Of Nitrogen, Phosphorus In Farmland Ecosystem In Dianchi Lake Basin

Water pollution has become more and more serious as the nutrient loss in the vegetable cultivation of Dianchi Lake. Based on this status, with application of Nutrient Differences Management (NDM) in the cropping of Lettuce and Lactuca sativa, crop products, nutrate contents, nitrogen and phosphorus nutrient utilization, soil nitrogen and phosphorus, organic carbon distribution, nitrogen and phosphorus circle and balance features of farmland ecosystem under different nitrogen and phosphorus content levels were studied in this paper. Therefore, the appropriate nitrogen and phosphorus fertilization levels can be found to guarantee the farmers' economic benefits, hence with the maximum of environmental benefits, which will relieve the nitrogen and phosphorus pollution load of non-point source pollution in Dianchi Lake. The main results showed that:1. The crop yield could be improved with the increase of nitrate fertilization under NDM. There was no obvious yield increase, even yield reduction with too much nitrate fertilization. The lettuce carried comparative high yield of 28968.75 kg·ha-1 under T3(N9oP126K180), instead lactuca got high yield of 47373 kg·ha-1 under T5(N848P316K792). There was no significant impact of phosphorus fertilization of the season on crop yield.2. In different duration periods, the utilization ratio of nitrogen and phosphorus for crops were obviously lower than the average of China. Under the certain amount of phosphorus and K, over use of nitrogen fertilizer cannot improve the nitrogen utilization ratio of crop yield, instead to enhance the loss of nutrient. Under certain levels of nitrogen (phosphorus), the relative crop phosphorus utilization ratio showed a whole declining trend.3. The total amount of nitrogen, phosphorus, available nitrogen and available phosphorus in lettuce cropping area soils showed a decreasing trend in vertical gradient. In different duration periods, the amount of total nitrogen, total phosphorus in different soil levels under different treatments turned out an irregular pattern. In harvesting period, total nitrogen(available nitrogen), and available phosphorus amount of the surficial soil showed correlations with the amount of nitrogen and phosphorus treatments in the cropping season; during the growth period, total phosphorus amount showed positive correlation with the amount of phosphorus treatment in the cropping season.4. The total nitrogen, available nitrogen, and available phosphorus amount of Lactuca sativa in its cropping area soils vertically showed a similar pattern with lettuce. However, the phosphorus under certain treatments had signs of gradually moving down. Total amount of nitrogen in surficial soils showed a whole growing trend in the cropping season; available nitrogen amount of the surficial soil shows correlation with the amount of nitrogen treatment on planting season. The Soil Available Phosphorus mainly located in the soil from 0 to 40 centmeter.5. The vertical change for organic carbon content in two planting areas was as follows:0-20cm>20-40cm>40-60cm. The organic carbon content in all the disposed surface soil was lower than those of the other two soil layers. The highest organic carbon reserved amount of Lettuce and Lactuca sativa in cropping area were found under the treatments of T6(N406P0K633) and T4(N565P316K792), reaching respectively 156.75t·ha-1 and 116.12t·ha-1.6. With the analysis from circle and balance features of nitrogen and phosphorus in farmland ecosystem, the result showed that the residue amount of phosphorus were higher than those of nitrogen. The inputs of nitrogen and phosphorus for each treatment could both meet the absorb requirements of crops growth. The surplus amount of nitrogen and phosphorus under high nitrogen and phosphorus fertilizer treatments (T5 and T8) was generally higher than those of the other treatments.7. The best nutrient management mode were found after general considering crops yield and the loss of nitrogen and phosphorus under NDM, therefore to achieve the balance of environmental and economic benefits. Besides, the best optimum combination of nitrogen and phosphorus treatments for lettuce was found asT6 (N406P0K633), for Lactuca sativa as T3 (N282P316K792).