| This paper takes the typical farmland of Hetao irrigation area in the Inner Mongolia as the study background, field test, data analysis and combined numerical model as the research means to analysis the influential factors and changing rules of the underground water as well as the groundwater quality, to study the dynamic changes of pollutants in the process of pouring out during the autumn irrigating, to evaluate the changes of the groundwater environment in the predicted area.The research found that the water level underground of the test area are decreasing year by year and growth period of crops also show a certain regularity because of the irrigation degree. The way of fertilization has a correlation with the concentrations of different underground water pollutants, it’s TN concentrations is rising in the crops’growth period, the underground water ammonia nitrogen and TP concentrations are increasing after fertilizing, salinity has quiet well correlation with the underground water level. The water salinity will decrease when the underground water level increased, vice versa. And, the concentrations of underground water pollutants will rising year after year when the water level dropping at the same time, then this two will have a noted contra-correlation.In the same period of Autumn irrigation, the concentrations of pollutants in the pouring out channel will be restricted by the water flow,so the pollutants’concentration are low due to the rich water flow.;The water flow has a small influence on each pollutant in different periods, the concentrations of pollutants won’t have much changes if the water flow decreased. Due to the reduce of water irrigation and the expand of the planting area, the pollutants’concentrations in the pouring out channel is rising year by year. Following the recession of the water on the ground surface, the concentration of TN will exceed1.Omg/L as well as the COD,40mg/L in the residential area. During the process of water recession and the increasing of the water flow, those pollutants’concentrations on the ground surface will dropping, the infiltration will increasing along the direction of water recession, the concentration of TN, TP of underground water will rising and the salinity has a trend of declining.In the process of water recession, the water displacement and the water infiltration are taking the proportion of1:10, the more the water irrigation,the more water infiltration, which lead to a majority remain of pollutants and minority remove out of the irrigation area, so this area is existing as the situation of pollutants remaining. Ninety percent of fertilizer remain in the irrigation area and only ten percent is removing out of the area by water, which will result in a serious pollution because of the irrigation.Through field scale test, through the calculation about the amount and groundwater concentration correlation, based on the environmental benignninig development conditions of the groundwater, the nitrogen content of the quality about underground water to Ⅳ standard is:wheat:N<51.1kg/hm2, sunflower:N76.77～81.8kg/h m2。The declining of the water level underground and the function of salt-leaching in Autumn pouring will ease the salting of soil. Through the prediction of model, salt in the water underground is showing a ascendant trend under the component irrigation and fertilization method. From a long-term interests, the rise of salinity is not good for the growth of crops. In not destroying the soil environmental conditions, increasing irrigation water in crop growth period (from may to September), control groundwater depth in0.6-0.8m. Reduced irrigation water in autumn poured period, control groundwater depth in0.5～0.6m. Making reasonable irrigation methods, in order to ensure the quality of the soil condition, be helpful for improving control groundwater environment. |
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