Study On Soil Nitrogen Release And Regulation Mechanism With Reclaimed Water Irrigation

Water shortage is a major challenge for the agricultural irrigation. However, reclaimed water will effectively ease the current situation. Because nutrient concentration is higher in reclaimed water, it is used improperly will bring adverse effect on crop growth and soil environment, may lead to agricultural non-point source pollution. In order to solve the rational application of fertilizer with reclaimed water irrigation, and providing theoretical basis for safe utilization of reclaimed water in agriculture. This study adopted methods of field plot experiment and indoor cultivation, soil urease and catalase activities of 0~10 cm, 10~20 cm, 20~30 cm, 30~40 cm and 40~60 cm soil layers were determined after tomato harvesting under reclaimed water(Re) irrigation and clean water irrigation(CK) from 2011 to 2014. Quality indexes and yield of tomato, soil urease activity, saccharase activity, amylase activity, catalase activity and the profit and loss situation of soil mineral nitrogen and total nitrogen in the growth period were analyzed in 4 fertilization treatments under different nitrogen levels with clean water and reclaimed water irrigation. The experimented soil was composed of the greenhouses soil with reclaimed water and clean water irrigation at Hongmen experiment station in Xinxiang, Henan Province. Using the method of indoor thermostatic incubation, soil ammonium nitrogen, nitrate nitrogen and total nitrogen of the samples were measured in 7, 14, 21, 28, 35 and 42 days. At the same time, the changes of soil nitrogen cumulative mineralization and nitrogen mineralization rate were analyzed. Soil nitrogen release characteristics were studied under different nitrogen rate with reclaimed water Irrigation. The main results were as follows:(1) Along with the extension of reclaimed water irrigation years, soil urease activity increased, at the same time, the root layer soil urease activity under reclaimed water irrigation was higher than that under clean water irrigation, which illustrating that reclaimed water irrigation promoted the formation of mineral nutrients and enhanced soil nitrogen supply capacity. Reclaimed water irrigation could improve the activity of soil catalase, and catalase activity under long-term reclaimed water irrigation was higher than that under clean water irrigation, which indicating that reclaimed water irrigation strengthened the detoxification of soil, improved soil buffer performance and increased crop’s ability to adapt to the soil adversity.(2) The reclaimed water irrigation increased soil urease and amylase activity, but decreased saccharase activity. Under different nitrogen levels, soil urease activity, saccharase and amylase activity of high nitrogen treatment, catalase activity of low nitrogen treatment and soil total nitrogen content after tomato harvest with reclaimed water irrigation were less than clean water irrigation treatment. Compared with no fertilization treatment under the same irrigation water, reclaimed water irrigation fertilization treatments improved saccharase and catalase activity, but reduced urease and amylase activity, clean water irrigation fertilization treatments promoted urease and saccharase activity, but inhibited amylase and catalase activity. Under the condition of no nitrogen, reclaimed water irrigation reduced soil catalase activity than clean water irrigation. Soil mineral nitrogen variation with reclaimed water irrigation increased significantly than clear water irrigation, and reclaimed water irrigation fertilization treatment decreased soil mineral nitrogen variation. This study shows that moderate amount of reducing nitrogen supplemented with reclaimed water irrigation treatment was an effective measure to raise the soil nitrogen supplying capacity and self-purification ability, enhance the capacity of soil detoxification and soil fertility, reduce the emissions of reclaimed water and nitrogen fertilizer. Different nitrogen levels with reclaimed water irrigation significantly influenced soil urease, saccharase, amylase, catalase activity, soil mineral nitrogen content and total nitrogen content.(3) Comparing with clear water irrigation conventional nitrogen treatment, reclaimed water irrigation and reduce 20% nitrogen treatment increased tomato yield significantly, vitamin C content and soluble sugar content in fruit were the highest. Organic acid content in fruit of reclaimed water irrigation conventional nitrogen treatment was the highest, but sugar-acid ratio reduced significantly than clear water irrigation conventional nitrogen treatment. The results indicated that moderate amount of reducing nitrogen supplemented with reclaimed water irrigation treatment increased significantly tomato yield and improved nutritional and flavor quality of tomato.(4) The overall performance of soil nitrogen mineralization characteristics was that soil nitrogen mineralization was faster at the early stage of incubation, and the release of nitrogen was higher than the middle and later periods, nitrogen mineralization cumulant of reclaimed water irrigation conventional fertilizer soil and reduce 20% nitrogen treatment was the largest. The result showed that A(N160)treatment stimulated the soil microbial activity and soil biochemical properties with reclaimed water irrigation, and soil nitrogen supplying capacity and nitrogen use efficiency were significantly improved. Greenhouse vegetable soil nitrogen mineralization rate declined obviously with the increase of incubation time showed that the difficulty level of soil organic matter decomposition and the change of microbial population characteristics effected nitrogen mineralization rate. Freundlich linear isothermal adsorption model and first-order kinetic model were fitted to soil adsorption parameter and nitrogen mineralization potential. A(N160) treatment for mineralization potential of soil coupling model(N0 = B0 + 117.5072t-0.1062) was established under the condition of different soil background values. The biological characteristics of soil nitrogen depend on exogenous nitrogen. This indicated that N160 treatment with reclaimed water irrigation was a kind of effective mean to improve the soil nitrogen biological effectiveness and soil nitrogen supplying potential.