The Dynamic Change Model Of Soil Water In Caragana Shrubland On The Loess Plateau

In the arid and semi-arid area of the Loess Plateau, the loess soil is deep, the annual rainfall is not much, and there is short of water resources, so there is no irrigation in most parts and precipitation becomes the only source of soil water. Soil water is also a significant factor affecting plant growth in the water-limited area. In recent years, the relationship between plant growth and soil water has disordered and the phenomenon of soil drought has appeared in most perennial plantation and grassland in most areas of the Loess Plateau. When the soil water content declines to a smaller value, a dried soil layer would appear under the maximum rainfall infiltration depth. The dried soil layer is called permanent dried soil layer,which not only blocks infiltration recharge of rain to the groundwater, but also has seriously affects on the absorption of soil water by plants, and lead to a more arid microclimate in local,which poses a serious threat to the ecological environment. Therefore, it is essential to have a study in the soil water in water-limited area, in order to hold the dynamic rule of soil moisture and to offer guidance on the best time to regulate the plants.For the factors of landform and land use have a huge influence on the distribution of soil water, the soil water have dramatic spatial variability on the loess plateau. Consequently,it enhances the difficulty to establish a mathematical model about the dynamic change of soil water. However, there are few studies in the area of the change features of soil water on the loess plateau. It is valuable to research in the area of the dynamic change model of soil water.This paper have a deep research on the soil moisture in the caragana shrub land in the arid and semi-arid area of loess plateau, which are the vertical variation of soil water and the soil water change features with time in different soil layers. Then, it has established corresponding mathematical models in this paper, which are validated by the soil water data observed in the plantation in the test area.Firstly, the soil water change model established by compartment analysis method is improved in this paper, and the modified model is obtained.Then, on the basis of the modified model of the vertical variation of soil moisture, it establishes a dynamic model of the soil water changes with soil depth and time.Furthermore, the modified model are validated by the soil water data observed during this period of 2002-2006 at Shanghuang Eco-experiment Station and the soil waterdata observed from 2012 to 2014 at 2.0 test plot in the caragana shrub land. In addition, the soil water data of 2002 and 2004 are selected to validate the dynamic model of the soil water changes with soil depth and time.The results show that:1. The modified model is used to fit 13 sets of soil water data observed in 2002, and all of the goodness-of-fit match the statistical requirements. But also by the comparison between the original model and the modified model, it can be found that the modified model can better represent the vertical distribution feature of soil water under different conditions in caragana plantations in the water-limited region of Loess Plateau.2. Through the analysis of the fitting parameters, the thirteen kinds of cases in 2002 can be classified into four groups according to the parameter values. The four types can represent interactions between plants and soil water under different rain conditions and different periods of plant growth. In addition, the data observed in different years and different stages of plant growth are selected to further analyze the reliability of the modified model. Then, for the above four sets of data, the goodness-of-fit are in compliance with the statistical requirements, and suggests that the modified model can has widely applicability and the reasonable of the classification.3. The soil water data of 2002 and 2004 are selected to validate the dynamic model of the soil water changes with soil depth and time, and the goodness-of-fit are in compliance with the statistical requirements. It illustrates that the model can well describe the dynamic change features of soil water in partial drought years, and provides guidance on the control of the relationship between plant growth and soil moisture.The results will lay foundation for estimating the soil water resources use limit and soil water carrying capacity for vegetation, and provide theoretical ground for the control of soil drought, the vegetation restoration and sustainable use of soil water resource. They have certain application values in the improving of ecological environment.