Abstract: 【Objective】The aim of this study on the steppe soil in Qinghai Lake area is to explore the soil moisture migration and its enrichment characteristics, soil moisture distribution model, hydrological cycle and balance and reveal the characteristics of soil reservoirs, dried soil layer and its recovery conditions, and then provide a scientific basis for protecting soil water resources and steppe vegetation, construction of soil reservoir and sustainable development of grassland ecological environment.【Method】A series of experiments were performed to determine soil moisture, soil suction, infiltration rate and particle size. More than 600 soil moisture samples were collected by Light-duty Human Drill in 2009-2012. Drying weighing method was used to determine soil water content. Bicyclic infiltration method was used to determine soil infiltration rate in situ. Soil particle size was analyzed by Laser Particle Analyzer. Soil suction was measured by Tensiometers in situ.【Result】The distribution of soil water at soil profile has a certain stability, that is, in dry season or rainy season, the soil water in this area is enriched about 65% at 0-0.4 m depth and is quite shortage under 0.6 m depth. The soil suction in this area ranging from 0.17 MPa to 0.42 MPa suggests that field capacity of this area is about 20%. The infiltration rate of soil in this area varying from 1.3 mm·min^-1 to 3.0 mm·min^-1 shows that it is high and advantageous to precipitation into soil. The soil moisture is about 23% and 6.5% at 0-0.4 m depth and under 0.6 m depth, respectively. Field capacity of this area is about 20%, meaning that there is about 3% gravity water at 0-0.4 m depth of soil. The soil usually develops a dried soil layer with different levels under about 0.6 m in this area, and the greater soil thickness, the more seriously dried soil layer develops. Under 0.4 m depth of soil, the relationships between soil moisture and depth can be described by power function. The parameters of power functions (i.e. a, k) are able to well reflect the average level of soil moisture (a) and the degree of soil moisture decreased with the increase of depth (k). As the precipitation increased by about 50 mm from 2009 to 2011, the increment of soil moisture can be clearly reflected by the incremental curve of analogue function. The increment of soil moisture within the depth from 0.4 m to 0.8 m gradually decreased from 5% to 3% and was less than 3% under 0.8 m depth. The soil property is excellent in this area, but the soil moisture under 0.6m depth is close to or below 5% unavailable water of silty soil.【Conclusion】The retention and enrichment of soil water at 0-0.4 m depth is rare and this characteristic mainly depend on the low temperatures and long-term freezing of soil in Qinghai Lake area. The regulation function of soil reservoir is weak in this area due to the average thickness of soil is less than 1.5 m. To some extent, the retention and enrichment of soil water not only can enhance the regulation function of soil reservoir for vegetation in shallow root, but also can play an important role in inhibiting the occurrence of grassland desertification. The soil water balance in this area showed a weakly positive balance because of 400-420 mm annual precipitation from 2009 to 2011. Under this condition, the dried soil layer in thin soil was able to disappear completely, but could not in thick soil. The dried soil layer was recovered slowly in this area and its soil moisture recovered was less than 5.0%. Development of dried soil layer and its distribution with small depth not only show that the ecosystem in this area is more vulnerable, but also indicate this area is not suitable for growing arbor vegetation because it will consume more water.

Key words: Qinghai Lake area, soil moisture, soil moisture simulation, distributed model, soil moisture retention, soil reservoir