Changes in the physical properties of soil in forestlands after 22 years under the influence of the Conversion of Cropland into Farmland Project in Loess region, Western Shanxi Province
The physical properties of soil such as soil particle size distribution,bulk density,and porosity are interrelated and have important effects on soil fertility and hydrological processes.Such processes include surface runoff,infiltration,groundwater recharge,and water yield.Excessive soil erosion in the Loess Plateau has resulted in severe degradations of the physical properties of the soil,such as increased bulk density,reduced aggregate stability,and reduced water retention.Soil properties are likely to change when large vegetation restoration efforts,such as the Conversion of Cropland into Farmland Project (CCFC) in China,are implemented.These changes in soil properties can affect vegetation coverage,litter accumulation,root penetration,and soil biological activity.Three typical arbor forests,which were converted from farmland 22 years ago in western Shanxi Province,were selected to study the depth and extent under the influence of the CCFC on the physical properties of the soil.We examined soil density,soil total porosity,and capillary porosity using field sampling and laboratory analysis.These arbor forests included Quercus wutaishanica,a natural recovery forest (NR),Pinus tabulaeformis× Robinia pseudoacacia,an artificial mixed forest (MF),and Robinia pseudoacacia,an artificial pure forest (PF).Cultivated lands (CK) were chosen as the control.Results of the study revealed that:1) compared to the cultivated lands,there were significant changes in soil bulk density above the 80 cm soil layer of the natural recovery forest (P＜ 0.05).There was an average reduction in soil bulk density of 28.78％ and the largest variability was found in the 10-20 cm soil layers.Compared to the control,soil density above the 60 cm layer of the artificial forests,MF and PF,was reduced by 10.58％ and 8.34％ respectively,and the differences in the 20-40 cm layers were the most significant,2) the total soil porosity above the 80 cm soil layer in three kinds of farmland increased significantly compared to cultivated land (P＜0.05).The ranking of total soil porosity from highest to lowest was:NR (35.53％) ＞ MF (15.04％) ＞ NR (13.68％),and the largest variability was found in the 20-40 cm layers,3) the soil capillary porosity of NR,MF,and PF were respectively 1.36,1.13,and 1.12 times those found in the cultivated land.The most obvious change of the natural recovery forest and artificial forest were found above the 80 cm and 60 cm layers respectively.The most drastic change was found in the 40-60 cm layers in both forests,and 4) the organic soil matter and clay content had significant effects on the physical and chemical properties of the soil.The increase of organic soil matter was as high as 31％,and interpretation of the clay content was between 44％ and 51％ of the change in soil bulk density,total porosity,and capillary porosity (P＜0.01).The results of this study suggest that the influence natural recovery forests have upon the physical properties of soil is greater than that of the artificial forests.This is mainly due to thicker litter and humus,superior biological diversity,more frequent microbial activity,and further developed tree roots in the natural recovery forests.
loess region of western Shanxi Provincethe conversion of cropland into farmland projectsoil physical propertiesdepthextent
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NSTL
万方数据
维普
