Experimental study of continuous stress-day index of water logging and excessive soil water as drainage standard of rice paddy fields

To explore the possibility of using the Continuous Stress-Day Index (CSDI) of waterlogging and excessive soil water as a drainage standard for rice paddy fields, consecutive and dynamic experiments on waterlogging and excessive soil water are conducted in testing pits during the heading and flowering stage of paddies. An CSDI model is developed to deal with waterlogging and excessive soil water issues. The model solution and the weight coefficient of waterlogging (C_W) are provided. The relationship of rice yield and CSDI is established through the analysis of experimental data. Results show that the stress and continuous stress from surface and subsurface waterlogging can reduce the rice yield in various degrees. The degree of yield-reduction is relatively high due to the continuous stress from surface and subsurface waterlogging. The weight coefficient C_W is a state variable that varies with the status of surface and subsurface waterlogging. A linear relationship between relative rice yield and CSDI can be observed under the condition of continuous stress from surface and subsurface waterlogging. Thus, the index CSDI can be utilized as a drainage standard for paddy fields, and the controlled drainage rules could be developed using the CSDI model.