喀斯特石漠化地区退耕模式对土壤团聚体组成和稳定性的影响

Effects of de-farming patterns on the composition and stability of soil aggregates in Karst rocky desertification area

探明贵州花江-关岭喀斯特石漠化地区不同退耕模式对土壤团聚体组成和稳定性的影响,为石漠化地区不同植被恢复模式的水土保持效益评估提供科学依据。选取喀斯特石漠化地区耕地(对照)、乔木林地和花椒林地土壤为研究对象,采用湿筛法测定0~40 cm土层土壤团聚体组成,计算>0.25 mm水稳性团聚体含量(R0.25)、平均重量直径(MWD)、几何平均直径(GMD)和分形维数(D)等团聚体指标。结果表明:1)耕地转变为乔木林地和花椒林地显著增加了粗大团聚体(>2 mm)含量(P<0.05),显著降低了<2 mm粒径团聚体含量(P<0.05);2)土壤R0.25、MWD和GMD值表现为乔木林地>花椒林地>耕地,土壤分形维数D值则相反;3)退耕后土壤团聚体稳定性的增加主要与粗大团聚体含量增加有关,2 mm和0.25 mm粒径是土壤团聚化过程中关键的临界点;4)退耕后,土壤团聚体含量和稳定性指标的变化幅度随土层深度的增加而减小,表明表层土壤团聚体组成和稳定性对土地利用变化的响应更为敏感。

This research aims to evaluate the effects of different de-farming patterns on the composition and stability of soil aggregates in the Huajiang-Guanling Karst rocky desertification area in Guizhou.The research results can provide a scientific basis for assessing the benefits of the soil and water conservation of different plants recovery patterns in Karst rocky desertification area.In this study,two de-farming patterns,namely,conversion of farmland to arbor forest land and Zanthoxylum forest land,were chosen with farmland as reference soil.The wet sieve method was used to determine the composition of soil aggregates in 0~40 cm soil layer,and calculate the aggregate indexes such as water-stable aggregate content(R 0.25),mean weight diameter(MWD),geometric mean diameter(GMD)and fractal dimension(D).The results showed that:1)The conversion of farmland to arbor forest land and Zanthoxylum forest land significantly increased the content of large macroaggregate(>2 mm)(P<0.05),and significantly reduced the content of<2 mm aggregate-size fraction(P<0.05);2)The values of soil R 0.25,MWD and GMD decreased in the following order:Arbor forest land>Zanthoxylum forest land>farmland,and the value of soil fractal dimension(D)was opposite;3)Correlation analysis showed that the increase in the stability of soil aggregates after de-farming was mainly related to the increase in the content of large macroaggregate.In the soil aggregation process,2 mm and 0.25 mm particle size may act as the key critical points,thus affect the composition and stability of soil aggregates after de-farming;4)After de-farming,the range of soil aggregate content and stability index decreases with the increase of soil depth,indicating that the composition and stability of surface soil aggregates were more sensitive to land use changes.