Influence Of Water Level Management On Water Quality Of Surface And Ground Water In Paddy Field

Irrational irrigation and drainage takes a lot of responsibility for the loss of great amount of fertilizer and pesticide, and result in the pollution of surface water. In order to illustrate the transfer and transform of fertilizer and pesticide, experiments were carried out in the Water-saving Park of Hohai University on rice paddy. Four regimes of water level control were set in each stage of rice; samples of water and paddy soil were collected and analyzed timely, data of both the soil and water environment were obtained. It has been illustrated that:The concentration of nitrogen and phosphorous increased remarkably in surface water of rice paddy after fertilization, decreased both in land surface water and groundwater according to the plant absorption and leaching, and become stable one week after fertilization. Pesticide application takes most responsibility for the rapid increase of COD in surface water of rice paddy, and COD decreased and become stable as the times goes on.Different regimes of water level control lead to different influence on the variation of water quality indexes of rice paddy.Land water level has little influence on TN concentration both in land surface water and groundwater. With the reduction of nitrogen absorption, TN concentration got the peak value in milk ripe stage. TP concentration both in land surface water and groundwater was low under the condition of flooding and non-water-layer, but TP concentration in groundwater increased in deeper surface water level treatments which was caused by leaching of phosphorous under the condition of high soil phosphorous absorption saturation. Under the condition of long time deep water layer, COD increased because of the high temperature and high obturation of plants density, but the COD never as high as do damage to the water quality. After cultivation, TN, TP and organic matter content in soil with flood irrigation higher than which in soil with controlled water supply, but it was the other way round on available phosphorous content.There were strong relationships between soil electric conductivity and soil temperature and moisture. The soil electric conductivity decreased with the increase of soil moisture and decrease of soil temperature.