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1 Polish Journal of Environmental Studies

1 2014

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Soil moisture status under deep-rooted and shallow-rooted vegetation in the semiarid area of loess plateau in China

100%

Xayan W. , Wanjun Z. , Zhiqiang W. , Xiuping L. , Shufen W.

nr 2

Deep loessial soil stores water recharged in a rainy season or wet year, and supplies water to vegetation for evapotranspiration in a dry season or dry year in the semiarid area of the Loess Plateau, China. However, this function of “soil water reservoir” may be weakened by deep-rooted shrub and forests that often extract deep soil waters and form a dry soil layer. The purpose of this study was to evaluate soil moisture status and variation under deep and shallow-rooted vegetation. The hypothesis was that the mature deep-rooted vegetation in this area may deplete deep soil water to such an extent that the plants could not further extract water from the deep soil layer, and the plants live mainly on present year precipitation. Soil moisture of shallowrooted annual crops and natural grasses, planted deep-rooted caragana shrub, arborvitae forest, pine forest, and the mixture forest of pine and arborvitae were tested in late 2001 and 2005-08 to 10 m depth. The maximum rain water recharge depths under shallow-rooted vegetation was 2.4-3.0 m, and those under deep-rooted vegetation were 1.2- 2.2 m in a relatively wet year of the five years. Within the maximum recharge depths, annual recharge depths and soil moistures were changed inter-annually dependent on rainfall. The average recharge depths for deep-rooted vegetation were 0.6, 1.0, 1.2, 1.4, and 1.8 m in 2005, 2008, 2006, 2007, and 2001, according to the ascending June-October rainfall amount order. In the inter-annually rechargeable layer, soil moistures under shallow-rooted vegetation were 6.7-13.6% in the five years, belonging to the easily or most easily available level in four out of five study years, the moistures under deep-rooted vegetation were 4.5- 12.0%, varying from hard-unavailable to easily available moisture levels dependent on rainfall. Below the inter-annually changeable layer to the tested 10 m, there were no significant inter-annual moisture changes (p<0.001) under both shallow-rooted and deep-rooted vegetation, but the moisture of shallow-rooted vegetation was >10%, belonging to easily available moisture level, those of deep-rooted vegetation were <5%, close to permanent wilting point, and the water belonged to or near to hard-unavailable moisture levels.