Influence of Native Soil Particles on Soil Aggregate Stability Relative to Breaking-down Mechanism
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National Natural Science Foundation of China (No. 41807068), the National Key R&D Program of China (No. 2017YFC0504902) and the Open Fund of Key Laboratory of Geological Hazards on Three Gorges Reservoir Area, Ministry of Education (China Three Gorges University) (No. 2018KDZ06)

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    Abstract:

    [Objective] Soil aggregates are the basic units structing soils, and their stability is an important index for evaluating soil breaking-down resistance under external forces. However, the current methodologies commonly used to analyze stability of soil aggregates rarely take into account influences of native soil particles on stability of soil aggregates relative to breaking-down mechanism. The purpose of this study was to fill up the gap by conducting an in-lab experiment.[Method] For the experiment, five undisturbed soil samples, 0-20cm in depth, were collected randomly using the S-shaped sampling method from each of the two tracts of land different in soil texture, one slope farmland of loamy sand soil in Shenmu County of Shaanxi Province, China and one newly established citrus orchard of sandy clay loam in Zigui County of Hubei Province, China. Following the LB (LeBissonnais) method listed in the international standard, the whole soil samples were pretreated separately with fast wetting (FW), slow wetting (SW), and mechanical breakdown by shaking after pre-wetting (WS) for analysis of breaking-down mechanisms of soil aggregates. At the same time, attempts were made to separate native soil particles from soil aggregates of various particle size fractions, so as to eliminate the influence of the former on fractionation of soil aggregates. Then soil aggregates in each fraction were treated with hydrogen peroxide to remove organic matter, and with sodium hexametaphosphate to separate native soil particles from skeletal materials of each fraction. The net mass of soil aggregates was obtained by substracting the mass of the soil aggregates of each particle size fraction in the soil samples treated with hydrogen peroxide and sodium hexametaphosphate from the mass of the soil aggregates in the soil samples before dispersion.[Result] Results show that two soils differ quite sharply in particle size distribution with the treatment. Mean weight diameter (MWD) was higher for the sandy clay loam soil than for the loamy sand soil regardless of breaking-down mechanisms. The two soils both followed an order of MWDfw < MWDws < MWDsw. Treatment FW is the most significant in affecting breakdown of soil aggregates, which is mainly attributed to pressure of the air enclosed in soil pores, and Treatment WS and Treatment SW follows. Based on the findings in this study, a new aggregates determination method is developed to verify the calculation results of the two selected regions. The influence of native soil particles on soil aggregate stability depends on soil texture and aggregates breaking-down mechanism and is much greater in the loamy sand soil than in the sandy clay loam, and exhibits an order of FW > WS > SW, in terms of breaking-down mechanism. The proportion of aggregate (>0.05 mm) to the total soil mass content (AR) before dispersion of the soil could hardly reflect stability of the soil aggregates. Variation of the AR before and after the influence of native soil particles is removed indicate that the influence of native soil particles is far more greater in the loamy sand soil than in the sandy clay loam.[Conclusion] The influence of native soil particles on aggregates varies sharply with soils type and treatment method. After eliminating the influence of native soil particles, AR can better reflect stability of the soil aggregates.

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XIAO Hai, GAO Feng, SHAO Yanyan, GUO Ping, LI Mingyi, ZHANG Lun, YANG Yueshu, XIA Zhenyao, XU Wennian. Influence of Native Soil Particles on Soil Aggregate Stability Relative to Breaking-down Mechanism[J]. Acta Pedologica Sinica,2021,58(3):649-656.

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History
  • Received:October 15,2019
  • Revised:February 27,2020
  • Adopted:April 14,2020
  • Online: December 07,2020
  • Published: May 11,2021