有机质影响溅蚀破坏土壤团聚体的主要作用机制

土壤有机质是团聚体的重要组成部分,其在团聚体形成过程中作用机制已有大量研究,但有机质在团聚体破坏过程中起何种作用尚未明晰,其对团聚体破坏过程中雨滴机械打击和消散作用贡献的影响也有待深入研究。为研究不同有机质含量对土壤团聚体的影响,选取5种不同退耕还林年限的土壤为研究对象,利用95%酒精和超纯水作为降雨液体,分别在4个高度下(0.5、1、1.5和2 m)对其进行溅蚀试验。结果表明:随有机质含量的增加,团聚体稳定性逐渐增强,土壤对雨滴机械打击和消散作用的敏感程度越来越弱,土壤抵抗侵蚀的能力越来越强;降雨前后大团聚体数量随着有机质含量的增加逐渐趋近相似,且酒精雨滴作用下的大团聚体含量明显大于超纯水作用下的大团聚体含量;在相同的降雨动能条件下,有机质含量增加使消散作用的贡献率呈现减小的趋势,且其对消散作用的影响在降雨动能较小时较为显著。研究结果对深入理解溅蚀过程中团聚体稳定性评价以及团聚体破坏因子具有重要作用。

Mechanism of Effects of Soil Organic Matter on Splash Erosion Disintegrating Aggregates

Objective] Soil organic matter is an important component of soil aggregate. Though much study has already been done on its role and mechanism in the forming of soil aggregate, little is available in the literature about its effects on splash erosion disintegrating soil aggregates and on contributions to the mechanical impact and slaking effect of raindrops disintegrating soil aggregates, too. So more studies need to be done in this aspect. The purpose of this study is to explore effects of organic matter content on breakdown of soil aggregates in splash erosion.Method] An indoor splash erosion experiment was conducted in the State Key Laboratory of Dryland Farming and Soil Erosion on the Loess Plateau, Institute of Soil and Water Conservation, Chinese, Academy of Sciences and Ministry of Water Resources, China. Soil samples different in soil organic matter content were collected from Fuxian of Shanxi Province for test in the experiment, which was designed to have home-made needle nozzles to simulate rainfalls of 95% alcohol solution and ultra-pure water, separately to distinguish effect of mechanical impact from slaking effect of raindrops on soil aggregates. The nozzle setting was designed to have four levels of height, i.e. 0.5 m, 1 m, 1.5 m and 2 m for controlling strength of the impact of raindrops.Result] Results show that of the five soil samples different in soil organic matter content, soil aggregate stability exhibited an order of MWD_SW > MWD_WS > MWD_FW, indicating that the higher the content of soil organic matter, the higher the stability of the soil aggregates and the higher the breakdown resistance of the soil. A significant relationship was observed between the content of organic matter and the stability index of soil aggregates. In soils high in organic matter content, the fraction of large aggregates (>0.25 mm) after the rainfall was approaching to that in proportion before the rainfall with the organic matter content increasing. The amount of large aggregates was significantly higher in the soil subjected with rainfall of alcohol than in the soil done with ultra-pure water. Splash erosion rate in all the five soils increased with rising height of the nozzles or kinetic energy of raindrops, regardless of type of raindrops and their relationship could be described with a power function. With rising kinetic energy of the rainfall, contribution rate of the slaking effect and mechanical impact decreased and increased, respectively. Under raindrops the same in kinetic energy, contribution of the slaking effect decreases with increasing organic matter content.Conclusion] Increase in organic matter content enhances stability of the soil aggregates and reduces contribution of the slaking effect in the process of splash erosion. All the findings in this study can serve as a scientific basis for evaluation of stability of soil aggregates and exploration of factors disintegrating soil aggregates during the process of splash erosion.