Study On The Lose Rule Of Agricultural Nitrogen And The Control For Pollution Of River Network

The controlling of farmland nitrogen pollution is an important measure to protect agricultural eco-environments, especially the water environment. Through leaching-pond orientation and farmland-scale experiment, this thesis have a good study on the loss rule of fertilizing-N in the fields of Shanghai suburban. What's more, this thesis still have a good study on the measurements to control nitrogen pollution in the river network from the following 3 aspects: source-controlling, process-controlling and terminal-controlling.Rice-wheat rotation and vegetable rotation experiments showed that NH4+-N was main nitrogen form in rice field surface water and its proportion in TN reached more than 90%. N03--N was main nitrogen form in rice, wheat, vegetable field leaching water and its proportion was about 85%～90%. Artificial rainfall experiment in rice, wheat and vegetable field indicated that it would lead to great nitrogen loss if there were rainstorm after fertilization. For example, loss coefficient of TN in rice field runoff was 18．33～26．32kg/ha if there was 80mm rainstorm after basal fertilization (187．5kg/ha); if there was 41mm rainstorm, loss coefficient of TN in dry land runoff could reach 9．49kg/ha 1 day after fertilization (75kg/ha). Leaching loss coefficient of TN in rice-wheat rotation and vegetable rotation was 36．59～45．12kg/ha and 8．81～28．38kg/ha, respectively. The leaching water quantity have been revised and it was made to be close to real value in farmland by using SCS method.Organic fertilizers application could markedly decrease runoff loss and leaching loss of nitrogen in rice field. Using organic fertilizers to replace 20～30% chemical fertilizers could reduce more than 30% TN loss in rainfall runoff, seeding-period and field-baking-period drainage, and could decrease 19．43～25．91% leaching loss of TN. In wheat field, using organic fertilizers to reduce 20% chemical fertilizers, in which refined organic fertilizers could reduce 2．59kg/ha leaching loss coefficient of TN, zymolytic pig ordure could increase 2．22kg/ha leaching loss coefficient of TN. Vegetable rotation experiment have been proved that appropriate refined organic fertilizers could cut down 12．8kg/ha leaching loss of TN when the same fertilizer quantity was used. The productivity testing showed that there was no apparent effect on rice, wheat and vegetable productivity if the usage-quantity of organic fertilizers was increased and chmical fertilizers was reduced. Therefore, using organic fertilizers in rice, wheat and vegetable field and reducing 20～30% chemical fertilizers, could alleviate nitrogen loss to water environment. The use of organic fertilizers is really a strong and effectual method to prevent the chemical fertilizers pollution to the water environment, but some non-technological measures must be taken to ensure it's comprehensive application.The study showed that the riparian plants system has obvious efficiency for the control of agricultural N pollution, which has 62% reduce ratio for NO₃^--N, and 44．39%～42．34% to NH₃--N, and in which Trifolium repens and Festuca Arundinacea are the most effective ones for the recondamination of NH3-N. Different depth experiment showed that the reduce ratio for TN in 1 m position is 40．81%～73．30%, with the average of 56．98%, which is higher than 0．7 m position, which read 16．54%～68．85%, with the average of 44．81%. what's more, Different deep position has no evident difference for the reduce ratio for NO₃^--N and NH₃-N.What's more, taking the west-north river network of Qingpu District for example, through constructing a mathematical model and validating, this thesis still have a good study on the effect of water-exchange to the treatment of river pollution. The results showed that this model can have a good simulating for the water-translating process if the boundary condition is enough. Existing irrigating works can't realize the self-depurating of west-north river network of Qingpu.