Study Of Soil Moisture Variation And Dynamic Forecasting Model In Farmland Of Henan Province

There is important significance to improve the ability of preventing drought, to set down plan of saving water irrigation, to enhance the water use efficiency in crop field if we can find out soil water variation law in the farmland, and if we can forecast the soil water dynamic variation. The productive climate conditions, especially precipitation and soil moisture in winter wheat and summer corn growing stages were analyzed in this article. Then the annual and vertical variation of soil moisture were analyzed in two spots of Zhengzhou and Nanyang. It can be divided into four periods: slow descending period, relative stable period, rapid descending period and increasing period. With regressive analysis, equations are established between the soil moisture in layer of 0~50cm and layer of 0~ 100cm when the rainfall is considered. Soil Water Deficit Index (SWDI) was defined. The reference crops water consumption is calculated with the Penman-Monteith Equation. Then the method was found to calculate SWDI after Crops Coefficient , Soil Water Stress Coefficient and Crop Water Consumption were calculated. Soil relative moisture and SWDI in main growth phases of winter wheat and summer corn were calculated and figures were drawn from Oct. 1995 to Sept. 1996 in Henan province. Six subarea were divided in Hennan province according to crops distribution, climate feature, soil types etc . The six subarea are North of Henan, East of Henan, West of Henan , Middle and South of Henan, South of Henan, Southwest of Henan. Then the distribution frequency of four grades of soil moisture in every subarea was calculated and analyzed in main growth phase with the data from 1995 to 2004. Soil water dynamic forecasting model of winter wheat and summer corn was established with the theory of soil water balance after the soil water variation was analyzed. The model accuracy is ± 8% with proof-testing.