Study On Water Restoration Of Dried Soil Under Different Mulching On The Loess Hilly Region

In the loess hilly region of north Shaanxi province where the climate is dry and rainless, vegetation over consumes soil water which would lead to the formation of permanent dried soil layer. If the moisture of dried soil can be recovered? How long will it take? It is the key concern of forestry, ecology, soil and water conservation and agriculture and many other subjects. It also has important theoretical and practical significance of agricultural production and ecological environment construction. In this study, we set 10 meters soil columns in the filed as a test object to observe and simulate the soil water recovery effects under different patterns of surface mulching(clean tillage, bluegrass cover, film mulching, branch mulching, and gravel mulching) in two year time, the results are shown below:(1) Results shows that the patterns of soil water vertical transporting on different time scale(annual, month, season) are similar. Its vertical transporting has obvious hystreretic effect, one rainfall which brings about one wetting front, its recharge possesses will brings last a long time. The later rainfall brings another wetting front push on the former to go ahead.(2) During 2014/5-2015/10, the depth of the water recovery under different mulching(clean tillage, bluegrass cover, gravel mulching, branch mulching, and film mulching) had reached 280 cm, 200 cm, 460 cm, 360 cm, 680 cm. Order of soil water recovery capability was film mulching, gravel mulching, branch mulching, clean tillage, bluegrass cover. There was a strong correlation between soil moisture storage capacity and precipitation under clean tillage, gravel mulching, branch mulching and film mulching, the rainfall utilization of were 17.9%, 36.1%, 28.0% and 94.3%, respectively.(3) In 2014 with rich rainfall, the depth of the water recovery under bluegrass cover reached 200 cm, soil water increased from 8.07% to 10.62% between 0-200 cm soil layer; Under the drought condition in 2015, soil wate has dropped to 7.89%, soil moisture was even drier than before. Compared with clean tillage and bluegrass cover, we know that, the water moisture storage of bluegrass was 84.9mm less than clean tillage during the growth period(2014/5-2015/12), then the gap between clean tillage and bluegrass cover dropped to 69.1mm during the non-growth period(2014/12-2015/5), so evaporation inhibition of bluegrass cover was 15.8mm. Soil water recovery capability of bluegrass cover was weak.(4) The Hydrus-1D model can be applied to simulating the soil water dynamic and distribution in the soil columns, compared with simulated and measured water contents under different mulching, determination coefficient(R2) were all above 0.9, and root mean square error(RMSE) were less than 0.01 cm3/cm3, and relative error(RE) were less than 3%. Simulation results could reflect soil water dynamic between treatments in a relatively long time. Simulated results showed that after a normal year infiltration depth of clean tillage, gravel mulching, branch mulching, and film mulching were 220 cm, 340 cm, 280 cm and 620 cm, soil moisture storage capacity increased 72.3mm, 139.2mm, 116.2mm and 417.0mm, respectively. Under continuous normal year, it will take 7.9 years, 4.1 years, 5.0 years and 1.3 years to recover the moisture in 0-600 cm dry soil layer.