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| Review of analytical methods for aggregate size distribution and water-stability of soil macro-aggregates |
| Wang Xiuying1,Gao Xiaofei1，2,Liu Heping1,Lu Bingjun3 |
| 1. School of Geography, Beijing Normal University,100875;2. State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, 100875;3. Beijing Soil and Water Conservation Centre, 100038： Beijing, China |
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Abstract Wet-sieving method is a classical and still the most prevalent procedure for testing the water stability of soil aggregates. Three main mechanisms are attributed to the breakdown of soil aggregates during wetting including slaking (breakdown caused by the compression of entrapped air in the soil pores), differential swelling and physic-chemical dispersion. The existing wetting methods can be divided into fast wetting and slow wetting according to the velocity of wetting, and atmospheric pressure wetting and high-vacuum wetting according to the barometric condition of soil sample when wetting. When soil samples are fast wetted under atmospheric pressure, water penetrates the soil mass at a high rate along capillaries, and compressing entrapped air causes a series of miniature explosions and breaks down soil aggregates, while wetting soil samples slowly or in vacuum gives high aggregation. In order to investigate the soil aggregate size distribution and water-stability comprehensively, it is recommended that fast wetting under atmospheric pressure and slow wetting (or wetting in vacuum) should be taken respectively with equivalent soil samples. During wet-sieving, the sieves should not shake too rapidly, and the number and aperture of sieves can be selected according to analytical purpose.
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Received: 02 June 2010
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