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Pore Size Distribution of Clayey Soils and Its Correlation with Soil Organic Matter

ZAFFAR, Malik, LU, Sheng-Gao
Pedosphere 2015 v.25 no.2 pp. 240-249
Vertisols, adsorption, clay soils, macropores, mercury, micropores, porosity, soil organic matter, topsoil, China
Soil pore size distribution (PSD) directly influences soil physical, chemical, and biological properties, and further knowledge of soil PSD is very helpful for understanding soil functions and processes. In this study, PSD of three clayey soils collected from the topsoil (0–20 cm) of Vertisols in Northern China was analyzed using the N2 adsorption (NA) and mercury intrusion porosimetry (MIP) methods. The effect of soil organic matter (SOM) on the PSD of clayey soils was also evaluated. The differential curves of pore volume of clayey soils by the NA method exhibited that the pores with diameter < 0.01 μm accounted for more than 50% in the pore size range of 0.001 to 0.1 μm. The differential pore curves of clayey soils by the MIP method exhibited three distinct peaks in pore size range of 60 to 100, 0.3 to 0.4 and 0.009 to 0.012 μm, respectively. In the three clayey soils, the ultramicropores (5–0.1 μm) were determined to be the main pore class (on average 35.5%), followed by macropores (> 75 μm, 31.4%), cryptopores (0.1–0.007 μm, 16.0%), micropores (30–5 μm, 9.7%) and mesopores (75–30 μm, 7.3%). The SOM greatly affected the pore structure and PSD of aggregates in clayey soils. In particular, SOM removal reduced the volume and porosity of 5–100 μm pores while increased those of < 5 μm pores in the 5–2 and 2–0.25 mm aggregates of clayey soils. The increase in the volume and porosity of < 5 μm pores may be attributed to the disaggregation and partial emptying of small pores caused by the destruction of SOM.