Effects of calcite on the soil porous structure: natural and experimental conditions

To evaluate the infilling of pores during calcification, we studied the pore size distribution of a sandy Calcisol by N 2 adsorption and Hg porosimetry. Carbonates were removed and the data compared with those from a Haplic A renosol before and after addition of calcite. Calcite addition induced variations in the pore volumes, which were purely addictive and depended on the porosity characteristics of the silicate plus organic fraction and CaCO3. I n the Calcisol samples, the removal of carbonates increased the pore volumes, but the mechanism cannot be explained by a simple additive effect. T he < 2 nm pores were affected by the non-carbonate soil fraction, the 2-50 nm size class was the most affected by calcification, while the infilling of the larger pores depended on the size and on carbonate contents. T he largest pores are infilled only when CaCO3 concentration is around 30%, while the smallest class determined with Hg intrusion is affected at about 15% of carbonates