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

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National Key Research and Development Plan Project (No.2016YFE0202900) and National Natural Science Foundation of China (No.41761144060) and Key Project of Foreign Cooperation of the International Cooperation Bureau of the Chinese Academy of Sciences (No.161461KYSB20170013)

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    [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 MWDSW > MWDWS > MWDFW, 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.

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LI Hairu, GUANG Huibing, LIU Gang, GU Ju, SHI Hongqiang, CHEN Hong, LEI Yuhong. Mechanism of Effects of Soil Organic Matter on Splash Erosion Disintegrating Aggregates[J]. Acta Pedologica Sinica,2021,58(1):106-114.

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  • Received:July 27,2019
  • Revised:August 06,2019
  • Adopted:November 04,2019
  • Online: October 30,2020
  • Published: January 11,2021