Study On The Fate Of Nitrate Nitrogen In Greenhouse Cultivated Condition

The particular environmental factors in greenhouse make soil having different physical and chemical features in greenhouse with those in open field soil. The greenhouse conditions leads to easy accumulation of nitrate in soil there by causing soil secondary salinization seriously. Nitrogen is unhealthful to people and animals, although it's a kind of indispensable mine nutrients to plant. What's more, nitrate is prone to be absorbed by plant and exuviated by water, result in water pollution. This test mainly study the transportation features of soil water and nitrate in greenhouse soil under distinct temperature,moisture and nitrogen fertilizer conditions as well as the nitrogen absorption effects of greenhouse plants due to disparate water and nitrogen fertilizer conditions.Through soil-column simulating experiment, the effects study of nitrate's transportation in greenhouse soil by soil water and temperature under evaporation condition provides water-fertilizer in greenhouse and environmental management with theoretical gist. The test results indicate: (1) The water content of soil section under 100mm has no obvious change while that above 100mm decreases gradually as close to the surface bit by bit. During first three days after evaporation began, the water content of surface layer decreases apparently, however, the decreasing extent becomes less in a large scale during two days afterward. Moreover, under conditions of high temperature or a great amount of initial water, the water content of surface soil will decrease quickly. (2)The soil nitrate content, which reaches the maximum at 0mm soil layer and increases from the 100mm soil layer to the soil surface gradually but nearly no change between 100mm layer and low-boundary, presents distinct phenomenon of surface gathering. The nitrate content of soil section transfers in upward direction attributing to the upward movement of soil water and the water content of soil section has palpable negative correlation with the nitrate content. (3) In greenhouse management, reasonable irrigation manner and capacity,feasible temperature and fertilization can reduce the excessive of the nitrate content of soil.Taking tomatoes as the crops for experiment, utilizing greenhouse salinized soil, the effects on nitrogen absorption of tomatoes by different soil water and disparate fertilization approaches were studied under simulated fields' environment condition, in order to explore and discuss the coupling action mechanism, from soil water and nitrogen, of the effects on the nitrogen absorption of greenhouse crops. The study results indicate: (1) Under the condition of this experimental level, the plants that were subjected to the treatment of 90%FC water and 150mg/kg nitrogen's fertilization grew better reflected by the high index of plants' biomass and roots' length, high activeness of nitrate reductase activity as well as little nitrate content. The plants that were subjected to the treatment of 60%FC water and 300mg/kg nitrogen's fertilization grew worse reflected by the low index of plants' biomass and roots' length, low activeness of nitrate reductase activity as well as more nitrate content. (2) The remaining nitrate and ammonium nitrogen contents in soil increases along with water decreasing and nitrogenous fertilizer's adding. The phenomenon of soil acidification and the secondary salinization of soil are serious. There is a serious situation of salinity's accumulation toward surface of ground causing the detriment of salinity. For absorbing nutrient by roots, the amount of nitrate and ammonium nitrogen increase along with the increase of distance to roots. The discrepancy of the contents of all-phosphors is not prominent due to their inconvenient movement in soil. Potassium in soil is abundant with over 350mg/kg's content of available K in upper layer soil. (3)Keeping providing adequate volume of water is convenient for plants' growth and biomass' accumulation and lessen the content of nitrate content in plants; On the other hand, a great amount of nitrogenous fertilizer will cause serious soil salinization and hamper the growth of plants and accumulation of biomass, furthermore, results in increasing amount of nitrate content in plants; The growth and biomass of plants were subjected to influence of due-pressing from both of the water content and high amount of nitrogen.