黄土丘陵区林草退耕年限对土壤团聚体特征的影响

Effects of forestlands and grasslands on soil aggregates under different vegetation restoration ages in loess hilly region

随着国家退耕还林还草战略的实施、植被覆盖的变化,林、草地植被恢复进程中土壤团聚体特征的变化受到广泛关注.本研究以黄土丘陵区西部的官山林场退耕后栽植的刺槐林地、撂荒草地为对象,选取退耕年限为10、25 a的林、草地,采用湿筛法测定各样地0~30 cm土壤的水稳性团聚体组成,比较退耕还林、还草和退耕年限(10、25 a)对土壤水稳性团聚体平均质量直径(MWD)和分形维数(D)的影响.结果表明:退耕10 a的林地0~30 cm土层水稳性大团聚体含量(R0.25)、MWD和D分别为57.60%、1.91 mm和2.73;退耕25 a的林地分别为60.17%、1.88 mm和2.74;退耕10 a的草地分别为59.89%、1.82 mm和2.74;退耕25 a的草地分别为72.69%、2.71 mm和2.61.进一步分析证明,随着退耕年限的增加,土壤团聚性增强;但林草地的变化存在差异:恢复10 a阶段,土壤团聚性林地尚优于草地,25 a后草地优于林地.各样地土壤的SOC含量与R0.25呈显著正相关关系(p<0.01),与D呈显著负相关关系(p<0.05).退耕类型和退耕年限对土壤团聚性有显著影响.

With the implementation of national Grain for Green plan,vegetation coverage changed dramatically in many areas. Wide attention has been paid on the variation of soil aggregates in the process of forestlands and grasslands restoration. In this paper,sites with different restoration types（secondary acacia forest and secondary grassland） and ages（10 a and 25 a） in Guanshan Forest Farm in the west of Loess Hilly Region were chosen as research objects. The effects of vegetation restoration types and ages on the contents,mean weight diameter（ MWD） and fractal dimension（ D） of soil water-stable aggregates in layer of 0 ~ 30 cm were investigated using wet sieving method. The results showed that Macro-aggregate content（ R0.25）,MWD and D were 57.60%,1.91 mm and 2.73 for 10 a forestland,60. 17%,1. 88 mm and 2. 74 for 25 a forestland,59. 89%,1. 82 mm and 2. 74 for 10 a grassland,and 72.69%,2.71 mm and 2.61 for 25 a grassland,respectively. Obviously,soil aggregates stability was enhanced with the restoration ages increased. Additionally,there existed some interactive effects.With the same restoration age of 10 a,soil aggregates stability of forestland performed better than grassland,while when restoration was extended to 25 a,the aggregates stability of the grassland were better than forestland. The parameters of R0.25,MWD and D were correlated with the content of soil organic carbon（ SOC） and the clay content. In conclusion,vegetation restoration types and ages have significant influences on soil water-stable aggregates.