Suspended organic matter removal from aqueous extracts of high pH soils - - ~

rganic matter and clay miner0 als in soils have negatively charged surfaces that act much like cation exchange resins. When more than 15% of the exchange sites are neutralized by Na+ and the final ionic strength of the aqueous extract is less than about 0.04 M, the clays and organic matter are dispersed. Under these conditions, the solution pH is usually greater than 8.4, and carbonate (COi-) and bicaibonate (HCO,) are present in the extracts. The dispersed organic matter stays in suspension (up to 0.2% by weight) and causes the extracts to be dark colored.' These unusually high-pH, high-sodium soils are designated as sodic or sodic soils. Ion chromatography (IC) has been adapted for anion analysis in soil extracts by Nieto and Frankenberger and by Skarie et al.293 The soils used in those studies had pH values below 8.2 . Conse,