the study of particle size distribution of calcium carbonate and its effects on some soil properties in khuzestan province

This experiment was carried out to study particle size distribution (psd) of carbonates in soils and its effect on some calcareous soil properties in khuzestan province, iran. soil samples (n=72) were collected from different regions. to evaluate the effect of carbonates on water contents at pressure head of 1500kpa and psd of soil samples, these properties were determined before and after removing their calcium carbonate. based on the results, removal of caco3 led to a change in psd in all the samples and 70% of those changed textural class. carbonates were most accumulated in clay and sand size in abadan region while they were accumulated in silt and sand fractions in other areas. also, evaluation of moisture retention at permanent wilting point (pwp) showed that this feature has been reduced in all samples after removal of carbonates. following these changes, verification of key to soil taxonomy equation [clay%= 2.5(% water retained at 1500 kpa tension%organic carbon)] in calcareous soils of khuzestan province showed that this equation can be used with high reliability in calcareous soils of abadan, karoon, hafttape agroindustries. however, this equation is not valid in amirkabir and debalkhozaiea groindustries. our fitted equation [clay % = (4.35*% water retained at 1500 kpa tension +35.3* % organic carbon)] has high reliability in predicting clay content in noncarbonate samples. this result suggests that the presence of carbonates and its distribution in soil particle size is an important factor in the variability of soil properties at arid and semiarid areas.