The Analysis And Simulation Of The Vertical Change On Soil Water Under Caragana Korshinskii Brush In Semi-arid Region Of The Loess Plateau

Loess Plateau, the cradle of the Chinese nation and the birthplace of ancient civilization,is the world's largest loess accumulation areas. It is one of the with the most-serious-soilerosion areas and the most vulnerable regions of the ecological environment in our countryand even in the world. There is not only an arid climate and serious soil erosion is, but alsoextreme shortage of water resources. Soil moisture is the main limiting factor for plant growthand development, and precipitation is the sole source of the soil moisture in these areas. Soit's very important and urgent that the research of dynamic change on soil water resources is.In order to reveal the mechanism of soil moisture dynamics in this region, and further studyon the impact of Caragana growth and development on soil moisture, the research of thevertical change on soil moisture has been taken in Shanghuang Ecological ExperimentalStation in hilly semi-arid of Loess Plateau.The data of soil moisture in the soil profile under Artificial Caragana Shrubs in thesemi-arid region of the Loess Plateau during April to November in the period from2002to2006were obtained by the neutron probe. A compartment model was used to study thevertical changes of soil water. The model was established by compartment analysis,asfollows：WC=ae^-k₁h-ce^-kh+f, a>0, c>0,k₁>0, k>0.This is a universal model. Under different rainfall conditions, it differs with differentparameter constraints and the model expression will be different:(1) With plenitude rainfall, the parameters satisfyk> k₁>0;(2)For the droughty soil with low water content, when there is rainfall into the soil, theparameters' constraint changes tok₁> k>0;(3) There is no rain for a long time, the model is simplified:WC=-ce^-kh+f, a>0,k₁>0.(4) When the soil adsorption force is extremely strong, soil water can't only beevaporated or evaporation capacity is very low, but also can't be sucked up by the vegetables'roots. When there is rainfall into the soil, the soil absorbs very quickly, the shallow soil watercan be complemented. So under this condition, the model can be simplified:WC=ae^-k₁h+f, a>0,k₁>0.The model above was be used to fit the data obtained from Shanghuang EcologyExperiment Station in Guyuan County of Ningxia Hui Autonomous Region. The goodness offit accorded with the need of statistics and the error of fit is also very low.The results showed:1. At start and end of the rainy season, the soil water is obviously different in the soildepth0-210cm, and it is0-270cm in wet year. In dry year, soil water (0-50cm) at thebeginning of the growth season differs from that at the end of it, but there is little differencebetween soil water (50-390cm) at the start and the end of the growth season. Because of theabundant rainfall in2003, the soil water has a deeper infiltration. As a result, when the rainyseason came, there are high soil water content and high difference on the soil depth (0-270cm)2. The soil water under wasteland is much more than that under Caragana Shrub land, atthe same time and same depth. The maximum infiltration depth under wasteland is2.3m, andis0.6m less than that under Caragana shrub land. But soil water storage (0-390cm) isobviously more, and the difference between them is large in wet year and period after thatyear, when the difference goes up and down among1600mm.3. Based on the above, the model was established. The vertical change of soil water afterrainfall can be expressed very well by the model with the parameters under specificconditions. The vertical change of the soil water varied at different time, and can be expressedby the model with different forms, too. It showed that the model can objectively reflect theprocess of precipitation infiltration.4. The vertical change on the difference between the soil water under wasteland andCaragana Shrubs can also be expressed by the model above, and the good result showed thatthe goodness of fit satisfied the need of statistics.The study can provide scientific basis for seasonable management of Caragana shruband building of stable vegetation, and have meanings to sustainable develop and utilize of soilwater under Caragana shrub lands in hilly semi-arid region of the Loess Plateau.