SURFACE-AREA OF SOIL ORGANIC-MATTER REEXAMINED

The specific surface area of soil organic matter has traditionally bee n considered to range from 550 x 10(3) to 800 x 10(3) m(2) kg(-1) base d on the change in ethylene glycol (EG) retention before and after tre atment of soils with H2O2 Recent studies, however, indicate that when N-2 is used as the adsorbate, the surface area of soil organic matter is approximately 1 x 10(3) m(2) kg(-1). To investigate this large disc repancy, the surface areas of four H2O2-treated soils were determined by EG retention and the N-2-Brunauer, Emmett, and Teller (BET) method. After exposure of the soils to H2O2, retention of EG decreased, while N-2 adsorption increased. The surface area of soil organic matter cal culated from the reduction in EG retention ranged from 65 x 10(3) to 4 81 x 10(3) m(2) kg(-1) and was dependent on the initial organic C cont ent of the soil. In contrast, the N-2-BET data yielded negative estima tes of soil organic matter surface area that varied from - 13 x 10(3) to - 410 x 103 m(2) kg(-1). These results demonstrate that techniques based on the removal of organic C fail to provide consistent and relia ble values for the surface area of soil organic matter. Due to the com plex nature of interactions between soil organic matter and EG, includ ing cation solvation, partitioning, and surface adsorption, it is reco mmended that EG retention be regarded as an estimate of the total upta ke capacity of soils for polar liquids, rather than a measure of surfa ce area.