Effects of Old-fields Successional Revegetation on Soil Moisture in Hilly Loess Region of Northern Shaanxi
2005, 20 (5):
In this article,effects of revegetation on soil moisture of old-fields were analyzed using multiregression and path analysis,based on once investigation of 0～300cm soil moisture of 17 sites with different abandonment years,11-times (once measurement of 0～500cm in growth season and ten times of 0～300cm)measurements of 10 sites,each measurement interval in profile is 20cm.The results show that:(1)As the related factors,such as aboveground biomass,vegetation coverage,soil organic matter etc.changed after abandonment,their effects to soil moisture content and fluctuation may vary in different post-abandonment stages.The measurements agree with the above facts,and confirmed that actually in local region,soil moisture content of old-fields tends to decrease,whilst fluctuation,denoted by standard deviation of moisture content,tends to increase after abandonment.(2)Soil moisture content and fluctuation can be estimated by topographic factors(slope gradient,slope facing and altitude),soil factors(bulk density of topsoil,organic matters) and vegetation factors(aboveground biomass,coverage),in which contents of top layers and fluctuation in root layers are determined mainly by communities coverage,while the aboveground biomass contributed most to the fluctuation of deeper layers.Both the communities cover and the aboveground biomass act mainly through its relative large positive and direct effect. (3)We found that down flux of soil moisture exists in the 260～300cm layer, deduced from the significant positive relationship between the difference of moisture reserves in 260～300cm and accumulative rainfall.In other words,the 260～300cm in profile is not the critical layer of rainfall compensation and plant usage,in our measurements,rainfall may seep beyond 300cm.This implies that evapotranspiration may be over estimated if calculated from the 0～300cm soil moisture content.So the accumulated leakage calculated by the 280～300cm soil moisture content is used as a supplement adjustor in multiregression to the estimated evapotranspiration.The evapotranspiration can be estimated by vegetation coverage,aboveground biomass,moisture flux in deep layer,slope gradient and direction,and topsoil bulk density.In which the primary influencing factor to communities evapotranspiration is aboveground biomass,vegetation coverage ranks the second.
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