The Study Of Nonirrigated Farmland Nitrogen And Phosphorus Loss Course And Environmental Effect In Shanghai

As the basic life elements in ecosystem, nitrogen and phosphorus are the main factors that limit crops grow. However, as the use of chemical fertilizer is increasing constantly, the loss of farmland nutrient aggravates the environmental pollution, which makes the farmland nitrogen and phosphorus loss issue attracts wide concern. Shanghai, the economic center of China as well as the key area of midstream and downstream and plain of ground division chief river, its water environmental pollution is becoming more and more serious for the unreasonable agricultural cultivation and fertilizer management, which not only cause the land to degradate and worsen with water environmental quality, but also bring greater pressure to sustainable development of the whole urban ecosystem., From March of 2004 to August, through continuous monitoring of loss situation of the nitrogen and phosphorus of the erosion silt, leakage and surface runoff in a typical farmland ecosystem of Baoshan District, the behavior mechanism of nitrogen and phosphorus loss, loss law, pollution load and impact on water environment have been studied, the characteristic of farmland nitrogen and phosphorus loss pollution have been found, and migration way and environmental effect of farmland nitrogen and phosphorus have been probed into. The result of our study is as follows:1. Change of nitrogen and phosphorus concentration in the edaphic section solution. During the period from March to August, the plantation cycle, as time goes by, the nutrient concentration tends to go down in the upper layer of the edaphic section but increases gradually in the deeper layer. In the depth of 120cm, the concentration increase greatly. Therefore, the fertilization of farmland places great pressure on the environment of groundwater.2. Change of phosphorus and nitrogen concentration in the leakage loss. Basically, the variation tendencies of TN and NO₃^--N concentrations are low - high - low - high, and the ranges are large, among which there are two obvious peaks. It proves that the concentration is influenced by the factors such as applied fertilizer, rainfall and plant. On the contrary, the range of NH₄^--N, NO₂^--N and TP concentration is very small in the plantation cycle. Running off with nitrate-nitrogen is very serious in leakage loss of TN, which accounts for 80% and the supreme concentration is 30.90mg/L, exceeding the standard of drinking water greatly.3. When it comes to surface runoff, the main carrier of the nitrogen and phosphorus loss is erosion silt, among surface runoff the proportion of sediment of runoff is: total nitrogen between 78.1%⁸2.2%, total phosphorus between 98.8%⁹9.4%.4. The total amount of nitrogen and phosphorus discharge from farmland with surface runoff and leakage two nitrogen and phosphorus output way in apply fertilizer district with 15%decrement is: total nitrogen 230.29kg/hm2, total phosphorus 27.73kg/hm2, there is 23.7% in the nitrogen used this season, and 19.9% in the phosphorus used this season. It causes the low-level fertilizer utilization ratio and a large amount of nitrogen and phosphorus loss to apply fertilizer excessively, which has formed the enormous pressure to water environmental pollution.5. The average concentration of the total nitrogen outputs in the whole year is: surface runoff 15.24mg/L, leakage 36.78mg/L; and the average concentration of the total phosphorus outputs in the whole year is: the surface runoff 0.29mg/L, leakage 0.06mg/L. Load to water environment of nitrogen and phosphorus loss of non-irrigated farmland of the whole year is, total nitrogen 237.93kg/hm2a, total phosphorus 0.89kg/hm2a. Take apply fertilizer district with 15% decrement as an example, we calculate the number of dropouts of annual average fertilizer that the non-irrigated farmland in Shanghai have 34,500 tons of TN and 1,200 tons of TP enter water environment every year through leakage and surface runoff (the value of apply fertilizer district normally should greater than this), all of those have accelerated the progress of wa...