Study On Forecast Model Of Lower Layers By The Soil Moisture Of Surface Layer

With the development of remote sensing technology, the soil moisture in big areas by the remote sensing data has been obtained large development. However, the soil moisture in only 0~20cm soil depth is relatively accurate. In this paper, the model research from the soil moisture in surface layer to forecast lower soil layers has been carried out and developed a small VB program to calculate the soil moisture in crop root layers, using the really measured soil moisture data and SAS software to obtain the models of soil water-storing capacity and soil volumetric moisture content, and analyzed the model accuracy. The main conclusions are shown as follows: (1) The model precision for the soil water-storing capacity is rather high. When the soil moisture in top layer changed rather slowly and lower layer soil changed quickly, also the soil water-storing capacity is shown nonlinear distribution, the model precision for the soil moisture can be reached more than 84% and 81% respectively in wheat and corn field. When under the situation of without rainfall or irrigation in longer times, the soil moisture in top and lower layers were total near the saturated and the change of soil moisture was rather small, the soil water-storing capacity is shown linear distribution, the model precision for the soil moisture can be reached more than 91% and 91.5% respectively. When the soil moisture in top layer changed quickly and lower layer changed slowly, the soil water-storing capacity is shown nonlinear distribution, the model precision can be reached more than 90% and 88% respectively. In whole appearing, the model precision of soil water-storing capacity, the minimum was 81% and the maximum was 95%. (2) The model precision by the soil volumetric moisture content was relative lower. When the soil moisture in top layer changed rather slowly and lower layer changed quickly, soil water-storing capacity was nonlinear distribution, the model precision only be reached more than 60% and 63% respectively in wheat and corn field. When under the situation of without rainfall or irrigation in longer time, the soil moisture in top up and lower layers were total near the saturated, and the change of soil moisture was rather small, the soil water-storing capacity is shown linear distribution, the model precision for the soil moisture can be reached more than 90% respectively in wheat and corn field. When the soil moisture in top layer changed quickly and lower layer changed slowly, the soil water-storing capacity is shown nonlinear distribution, the model precision can be reached more than 76% and 88% respectively. In whole appearing, the model precision by the soil volumetric moisture content, the minimum was 60% and the maximum was 94.9 %. (3) In fact, in the northwest region, there is no rainfall or irrigation in long times, so the soil moisture in top and lower layers changes rather small and most shown the linear distribution, In this case, the model precision was rather, in special for the soil water-storing capacity model. The model precision of the minimum was 91% and the maximum was 95%. The precision by the soil volumetric moisture content, the minimum was 90% and the maximum was 94.9 %. (4) Applied in practice, the soil water-storing capacity model was recommended in this paper Although obtained the result by the consequence using soil water-storing capacity model must calculate the soil moisture in each layer again, on the contrary, using the soil volumetric moisture content model can directly obtained the soil moisture of each layer. However, the model precision of the front was higher than the later, and the front can more actually reflect the situation of soil moisture distribution.