黄土高塬沟壑区植被恢复对沟头土壤团聚体特征及土壤可蚀性的影响

【目的】沟头是黄土高塬沟壑区发育最活跃的地貌部位,关系着整个塬坡沟系统的水土流失。探明黄土高塬沟壑区植被恢复对沟头土壤团聚体特征及土壤可蚀性的影响,为区域生态环境修复和水土保持效益评价提供科学依据。【方法】以仍进行耕作利用的农地沟头为对照,研究撂荒后自然恢复植被沟头不同土层（0—10、10—25、25—40 cm）土壤团聚体特征及土壤可蚀性随植被恢复年限（3—30 a）的变化。通过干筛法和湿筛法测定土壤团聚体组成,计算>0.25 mm水稳性团聚体含量（WR_0.25）、平均重量直径（MWD）、几何平均直径（GMD）、团聚体破坏率（PAD）、团聚体分形维数（D）等团聚体特征值,测定土壤机械组成及有机质含量,计算土壤可蚀性因子（K）。【结果】（1）与农地沟头相比,恢复3—30 a植被沟头土壤WR_0.25、MWD、GMD分别增加11.49%—84.43%、0.18—2.05倍、7.53%—108.62%,三者随植被恢复年限的增加呈线性递增关系（P<0.01）,且均随土层深度增加而减小;（2）植被沟头土壤PAD、D随植被恢复年限增加以线性方式递减（P<0.01）,较农地沟头分别减小3.81%—32.14%、0.55%—6.63%,二者随土层深度增加而增大;（3）随着植被恢复年限增加沟头土壤可蚀性因子K以线性关系递减（P<0.01）,较农地沟头减小5.43%—14.44%,K随着土层深度增加而增大。【结论】植被恢复条件下有机质含量的提升对团聚体形成和稳定性起着重要的作用。沟头土壤可蚀性的减小与水稳性团聚体含量的增加、团聚体稳定性的提高密切相关,自然恢复条件下植被恢复22—30 a沟头土壤团聚体稳定性和抗蚀性能得到明显提升。

Effects of Natural Vegetation Restoration on Characteristics of Soil Aggregate and Soil Erodibility of Gully Heads in Gully Region of the Loess Plateau

【Objective】 Gully head was the most active geomorphic part in gully region of the Loess Plateau, which was related to the soil erosion of the entire slope gully system. This research aimed at evaluating the effects of vegetation restoration on soil aggregate characteristics and soil erodibility of gully heads in gully region of the Loess Plateau. The research results could provide a scientific basis for regional ecological environment restoration and soil and water conservation benefit evaluation. 【Method】 With the farmland as control check, an investigation about soil aggregate characteristics and soil erodibility of different soil layers (0-10, 10-25, 25-40 cm) with different natural vegetation restoration ages (0-30 a) of gully heads was carried out. The aggregates amount, water-stable aggregate content (WR_0.25), mean weight diameter (MWD), geometric mean diameter (GMD), destruction rate (PAD) and fractal dimension (D) were examined by dry and wet sieving methods. Soil mechanical composition and organic matter content were determined which were used for calculating soil erodibility factor K. 【Result】 (1) WR_0.25, MWD and GMD of vegetation gully heads increased by 11.49%- 84.43%, 0.18-2.05 times, and 7.53%-108.62%, respectively, compared with the CK (farmland of gully heads). These three indicators linear increased with vegetation restoration years increasing (P<0.01), and decreased with the increase of soil depth; (2) PAD and D of soil aggregate of vegetation gully heads decreased with linear increase of vegetation restoration time (P<0.01), which was 3.81%-32.14% and 0.55%-6.63% lower than that of CK, respectively. Both of them increased with the increase of soil layer; (3) K decreased linearly with the increase of vegetation restoration period (P<0.01), which was 5.43%-14.44% lower than that of CK, and K increased with the increase of soil depth.【Conclusion】The increase of organic matter content under vegetation restoration conditions played an important role in the formation and stability of aggregate. The decrease of soil erodibility of gully heads was closely related to the increase of water-stable aggregate content and stability of aggregate. Under natural recovery conditions, soil aggregate stability and soil anti-erodibility of gully heads were significantly improved during the restoration period of 22-30 a.