黄土丘陵区刺槐林土壤团聚体稳定性和土壤可蚀性动态变化

Dynamics Changes of Soil Aggregate Stability and Soil Erodibility of Robinia pseudoacacia Plantations in Hilly Region of the Loess Plateau

退耕还林工程是黄土高原控制水土流失的主要措施之一,探讨退耕还林对土壤团聚体稳定性与土壤可蚀性的影响,可为黄土高原地区生态恢复和水土保持效益评价提供科学依据。以农田为对照,选取不同退耕年限(5,10,15,20,25,30年)刺槐林为研究对象,研究退耕还林后0—30 cm土层土壤团聚体稳定性和土壤可蚀性动态变化,并探讨土壤可蚀性与土壤团聚体稳定性之间的关系。结果表明:(1)>0.25 mm水稳性团聚体含量、平均重量直径、几何平均直径随着退耕年限增加呈递增趋势,三者相比退耕前(农田)分别增加32%~79%,32%~98%,2%~60%。(2)土壤团聚体分形维数随着退耕年限增加呈递减趋势,较退耕前减少0.6%~6.0%;土壤有机质随着退耕年限增加呈递增趋势,较退耕前增加8.4%~38.9%。(3)土壤可蚀性因子(K)随着土层增加而增加,但随退耕年限增加呈递减趋势,随退耕年限递增(K)分别减少1.0%,2.7%,3.6%,3.9%,5.0%,7.9%。(4)退耕还林后,>0.25 mm水稳性团聚体含量和土壤团聚体分形维数是土壤可蚀性变化的主要驱动因子;地上生物量通过影响>0.25 mm水稳性团聚体含量和土壤团聚体分形维数间接影响土壤可蚀性因子(K),且总效应最大。退耕还林后地上生物量增加对土壤团聚体的形成与稳定,以及土壤可蚀性降低起着重要作用,且退耕还林可显著提高团聚体稳定性,降低土壤可蚀性。

“Grain for Green”Project is one of the main measures to control soil and water loss on the Loess Plateau.Discussing the impact of returning farmlands to forests on the stability of soil aggregates and soil erodibility could provide a scientific basis for ecological restoration and benefit evaluation of soil and water conservation on the Loess Plateau.In this study,the Robinia pseudoacacia L.forests with different planting years(5 years,10 years,15 years,20 years,25 years and 30 years)were selected as the research object,and the farmland was used as the control to study the dynamic changes of soil aggregate stability and soil erodibility in 0-30 cm soil layers after returning farmlands to forests,and the study also explored the relationship between soil erodibility and soil aggregate stability.The results showed that:(1)The content,mean weight diameter and geometric mean diameter(GMD)of water-stable aggregates>0.25 mm increased with the increasing of planting years,which increased by 32%~79%,32%~98% and 2%~60%,respectively,compared with that of farmland.(2)The fractal dimension of soil aggregates decreased with the increasing of restoration ages,which decreased by 0.6%~6.0% compared with that of before returning farmland.Soil organic matter increased with the increasing of restoration ages,increased by 8.4%~38.9% compared with that of farmlands.(3)Soil erodibility factor K increased with the increasing of soil layer,but decreased gradually with the increasing of restoration ages,and decreased by 1.0%,2.7%,3.6%,3.9%,5.0% and 7.9%,respectively,with the increasing of restoration ages.(4)After the conversion of farmland to forest,the fractal dimension of soil aggregates and the content of water-stable aggregates>0.25 mm were the main driving factors for the change of soil erodibility.The aboveground biomass indirectly affected soil erodibility through affecting the fractal dimension of soil aggregates and the content of water-stable aggregates>0.25 mm,and the total effect was the largest.The study suggested that the increase of soil aboveground biomass after returning farmlands to forests played an important role in the formation and stability of soil aggregates and the reduction of soil erodibility,and returning farmlands to forests significantly improved the stability of aggregates and reduced soil erodibility.