Transport And Transformation Of Nitrogen Element In Saline-alkali Paddy Soil

There are all kinds of saline-alkali soil around 100 million hm2 in China. The saline-alkali soil area in Songnen Plain, which is one of the three major saline-alkali soil concentrated distribution area, is up to 2.333 million hm2. Equally important to animal husbandry land for developing saline-alkali soil, farm land takes 28.7% proportion of the saline-alkali soil. In recent years, the way of planting on the saline-alkali soil aiming to improve saline-alkali soil grows more and more popular. However, it brings the new agricultural pollution issue:the agricultural non-point source pollution. Qianguo irrigated areas as the field experimented site is located in in Songnen Plain. Nitrogen loss of the paddy land in Qianguo is one of the heavily polluting sources for water environment. Because of excessive amounts, the low utilization, as well as the unscientific way of applying nitrogen fertilizer, the heavy loss of nitrogen becomes a serious threat to the Chagan Lake, the 4A class national ecological protection zone laying downstream.At present, the systematic research on dynamics, transport and transformation of nitrogen in soda saline-alkali soil as well as their potential impact to the environment is in great need. Therefore, researching on the nitrogen dynamic change law of saline-alkali paddy field is not only important for water and fertilizer, and the regulating of nitrogen loss, but will also bring good news to the management of saline-alkali soil and the protecting water environment cause. In this study, Songnen Plain soda saline paddy fields are selected as the research object, in two field experiments, based on the combination of laboratory simulation experiments to explore the saline paddy nitrogen dynamics, migration and transformation of its potential impact on the environment.The main objectives of this work are:(1) pilot area survey of the basic hydrology, climate and other basic conditions for two consecutive years of tracking and monitoring saline paddy nitrogen dynamics; (2) based on field experiments, taking the experimental area of undisturbed soil, elements in the laboratory for soil analysis, material balance analysis of soil nitrogen, ammonia volatilization experiments, nitrogen leaching and soil solid ammonium performance analysis and other experiments. By soil properties, nitrogen loss means the amount of fertilizer and other factors, in theory, analysis of nitrogen in saline paddy fields of migration and transformation rules; (3) propose the main channels and technical means to reduce nitrogen pollution with the main features of soda saline and local farm management measures.The main conclusions are as follows:1, The tested soil is rich in alkalinity, depending on the depth of soil layer; the contents of N, C and P are low and reduce with the depth of soil; the contents of Na, Mg, Al and Ca are higher comparing to other metals in soil and their contents increase with the soil depth; CEC of soil relates to of the soil montmorillonite and humic acid contents, and deep soil levels are greater than the shallow soil in the content, which can be attributed to the soil surface fertilizer.2, During the two year experimental period, the Ca2+ and Mg2+ content in paddy field surface water changed significantly. The total nitrogen (TN) and ammonia (NH4+-N) concentration reached its peak value after fertilization, and subsequently decreased with time. Heavy storm was observed to increase nitrogen runoff. The nitrate (NO3--N) content was observed to reach its peak value later than TN and NH3-N, and its concentration decreased with time. It was found that TN, NH4+-N and NO3--N decreased by about 78.4%～90.2%,41.9%～86.2% and 66.5%～87.1% respectively, which is an indicative of serious nitrogen leaching. The TN concentrations in paddy field runoff exceeded the National Surface Water Quality Standard (levelⅢ). In addition, the non-ionic ammonia concentration was very high, and could pose serious threat to the aquatic biota in Chagan Lake.3, Through the laboratory simulation experiment, in the flooded environment, with different fertilization nitrogen in surface water rarely loss in the form of ammonia volatilization, accounts for about 0.01% of the total loss; total nitrogen concentration in surface water and 30 cm Soil water are positively correlated with the amount of fertilizer, while concentration of total nitrogen in deep soil water has no significant correlation with fertilizing amount; different fertilization while the same layer loss of form by nitrate in saline-alkali soil, and the concentration of nitrate in deep soil is unrelated with the amount of fertilizer; saline soil contains a lot of salt composition and it effects nitrogen saturation quantity of soil, also be one of the important factors of promoting nitrogen fertilizer leaching loss.4, Fixation and release of ammonia is one of the important processes of inner cycle of soil nitrogen. Characteristics of soil ammonium fixation corresponds with the Langmuir adsorption isotherm and Freundlich adsorption isotherm and the Freundlich adsorption isotherm is better (r2 =0.9523) so that the soil adsorption of ammonia can be attributed to the multi-layer adsorption mechanism. Meanwhile, the soil adsorption of ammonium are enhanced by increasing ammonium concentration in solution. But through the observation of two isotherm type, the capacity of ammonium fixation of tested soil is low and the maximum adsorption capacity is 1.25 mg/g.5, BMPs are the primary measures to control non-point source pollution. By taking the measures of enhancement of fanning management, integrated soil fertility management, rational irrigation, construction of artificial wetlands and others and the local nitrogen pollution can be controlled.