Study On Progress Of Soil Moisture Changing In Loess Soil Column

The water resource is short, and rainfall is the only supply of soil water.Rainfall infiltration characteristics determine its effectiveness, including both crop and soil moisture restoration. Studyding on its characteristics and effectiveness against local rainfall is also lack of extensive reports in Mizhi. The studying on relationship between local rainfall characteristics and their infiltration is important for making full use of rainfall and soil moisture reasonable, simultaneously the regional ecological economic development. In the paper, through the 10 m soil column positioning observation in field and numerical simulation, analyzing the rainfall infiltration depth under natural rainfall, and estimating the interaction of infiltration from local rainfall characteristics :(1)The moisture content of soil layers within 0.3 m changed obviously when the single precipitation is 5.2 mm(light rain) after eleven hour with automatic monitoring, while that of below have almost no changes; the affect depth can be up to 0.6 m when single precipitation is 15.8 mm(moderate rain) within four days. The moisture content of 1.2 m changed obviously and that of 1.4 m have a slight rise when single precipitation is 33.6 mm(heavy rain) among eight days. Water cycle is mainly conducted over 0.8m of the evaporation zone, soil moisture of this layer evaporate easily,the changes of moisture content lag and the growth decreases gradually with depth below it.Vertical transporting of soil moisture has a hysteresis, the wetting front push on with a wave form, one rainfall bring about one wetting front, the later wetting font push on the former to go ahead.(2)The infiltration depth of jujube and bluegrass continues to increase, respectively, reach to 140 and 120 cm. In the early observation stage, the infiltration depth of alfalfa increases, but begins to decrease later. The infiltration depth of locust and korshinskii shows a rapid decrease trend when the month rainfall is small, reduced to 0 at the end of observation stage. A lot of shallow soil moisture has been consumed by vegetation’s growth, locust growth exacerbated soil desiccation further. Plastic mulch can significantly increase soil water infiltration, the amount of supply reach to 187.5 mm in observation stage, and soil moisture recharge of each cover shows that: plastic mulch>gravel>branch>bareland. Variation regulation of infiltration depth of each cover is basically the same, showing continuous upward trend. Under the same kind of rainfall intensity conditions, the maximum infiltration depth of each treatment is quite different. At the end of observation period, infiltration depth of plastic mulch and gravel respectively reach to 340 and 260 cm.(3)Using HYDRUS-1D model, adapting atmospheric boundary conditions with surface layer,simulating the soil moisture movement and distribution under typical rainfall in soil column, it was found that HYDRUS-1D model can better simulate the soil moisture movement and distribution under different typical rainfall, the actual value is smaller than the analog value under typical light rainfall in 10 cm, maximum RE is 0.59% under typical moderate rainfall, results of simulated and measured have a same regularity under typical heavy rain. RE does not exceed 1% in deep soil, the variation of soil water content does not exceed 0.2%, the model established is fit for moisture simulation of soil column.(4)Simulation results show that water content is consistent with the annual rainfall in 80 cm, susceptible to environmental factors. Due to the lagged effect of infiltration, changes of soil water content is always later than rainfall by one year at 100 cm in 1996-2000, effects to soil moisture from the previous year’s rainfall will show up in the second year. In consecutive wet years, deep soil can get a large water supply. Due to repeatedly push, the maximum depth of infiltration increase rapidly, that has nothing to do with the amount of rainfall, but the rate of increase has, and it also exhibit hysteresis, the maximum infiltration depth reachs 400 cm finally.