SOIL ORGANIC-MATTER INFLUENCE ON ADSORPTION AND DESORPTION OF BORON

The role of soil organic matter in B adsorption and desorption processes in soil is not yet clearly understood. Adsorption/desorption isotherms of B were compared in three soils before and after organic-matter removal by NaOCl. The amount of B adsorbed was considerably greater after the organic matter had been removed from the soil, and the release of B showed a hysteretic trend or, in any case, the hysteretic nature of the B release increased. An increase in oxalate-extractable Fe and Al occurred after destruction of the organic matter. It is suggested that a portion of the Fe and Al oxides, as well as other possible adsorption sites, are generally coated or occluded by organic matter and become active only after removal of the organic matter.