Research On Dynamic Characters Of Soil Moisture And Water Blance Of Forestland In Nanxiaohe Gou Basin

Soil water is the most important resource of the growing plant.Under the influence of many factors, such as precipitation, canopy interception, canopy transpiration, soil evaporation, runoff and surface seepage, soil moisture is changing. Precpitation is the only origin for soil, but evaporation and transpiration are major expenditzeres. Robinia pseudoacacia, Platycladus orientalis and Pinus tabulaeformis are major species that can conserve soil and water to improve ecological environment on the Nan-xiaohe Gou Basin. Studying water balance and soil moisture ecological characteristic of these three kinds of trees, a lot of experience can be acquired to guide our ecological environment construction and to recognize and evaluate the ecological and environmental effect of planted forest.This paper analyzed the precipitation, soil moisture dynamic, soil water balance and the major affected factors by using field survey and located observation. The main conclusions can be draw from paper as follows:(1) Analyzing the stastic precipitation in rescent 43 years in Nan-xiaohe Gou Basin, it shows that the multi-year average precipitation in growing season is 396.4mm, which is 76.2% of mean rainfall amount. Annual precipitation days are primarily focused on May to September, which are 56.9% of the annual rain days. By means of variability of mean-annual precipitation and mean-month precipitation we can reach a conclusion that the distribution of precipitation isn't proportional in a year or out of a year.(2) Soil water content of forestland has remarkable interannual and seasonal changeand, and put up definite regularity. Soil water content among different habitats is heavier in plentiful rainfall year than general rainfall year. Soil water content in growing season is divided into three Periods: consumption Period, precipitation recharge Period and restoring Period.(3) The change trend of soil water content in each layers from0cm to 100cm are basically in consistence.The soil water could be divided into three change layers: the quickly changing layer (0-20cm), the utilization layer (20-60cm) and the complementary layer (60-100cm).(4)The canopies of Robinia pseudoacacia, Platycladus orientalis and Pinus tabulaeformis in runoff plots have upstanding hydrological effects. They have different intercepting capability with the changing precipitation. Seen from the growing season, intercepting rate of canopy of Robinia pseudoacacia is the highest,which is to 28.7%.The rate of canopy of Platycladus orientalis and Pinus tabulaeformis is close, which is about 8%.(5) The soil water cycling of Robinia pseudoacacia, Platycladus orientalis and Pinus tabulaeformis in growing season is a positive balance, because income of soil water is higher than expenditure. In the whole growing season of 2005, evapotranspiration of Pinus tabulaeformis is the highest (360.2mm), Platycladus orriental takes the second place (357.2mm), while Robinia pseudoacacia is the lowest (288.4mm).In 2006, Platycladus orientalis is the highest (333.4mm), and its follower is Pinus tabulaeformis (329.8mm), and Robinia pseudoacacia is the lowest (260.5mm).(6) Potential evaporation is calculated by Penman-Monteith formula. Water consumption is calculated in growing season.It shows that the mean water consumption of Robinia pseudoacacia, Platycladus orientalis and Pinus tabulaeformis is very approach in 2005 and 2006, and it is biggest in July.