GEODER@4 Geoderma 74 ( 1996) 125- 137 Large effect of leaching of DOC on water adsorption properties of a sandy soil Grzegorz Jbzefaciuk a3 * , Zofia Sokolowska a, Mieczyslaw Hajnos ‘, Christian Hoffmann b, Manfred Renger b a zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCB Institute ofAgrophyics; Do&viadczalna 4, P.O. Box 121, Lublin. Poland ’ Institute of Ecolo~Ty, Dept. of Soil Science, Technical Unillersity Berlin: Sekr. BK. Sal,-ufer II- 12, D-10587 Berlin, German> Received 22 September 1995; accepted 13 June I996 Abstract In this study, changes of adsorption properties of a sandy soil from a former sewage farm due to the leaching of dissolved organic carbon (DOC) were examined. The leaching of DOC at various pH levels was simulated in laboratory experiment using sodium hydroxide as the leaching agent. An increase of pH resulted in an increase of the amount of DOC in the studied soil. The removal of DOC altered the surface properties of the remaining solid. In particular, the surface area was reduced and the water vapour adsorption energy distribution function was shifted to lower energy ranges, thus showing the increase of the hydrophobic character of the soil. The intensity of these changes was more pronounced when the soil had been previously acidified. Key w ,ordJ: water adsorption; DOC; pH: sewage farming 1. Introduction Dissolution of organic carbon affects a number of different processes in the soil and has a predominant importance for nutrient and contaminant mobility, microbial activity, mineral weathering and acid-base equilibria in soil (Vance and David, 199 1; Andersson et al., 1994; Curtin and Smillie, 1983; Bishop et al., 1994). The pH of soil solution is the main factor governing the dissolution of organic carbon. An increase of pH leads to an increase of DOC content, while the effect of soil acidification on DOC can be either * Corresponding author. Fax: +48(81)45067. E-mail: jozefaci@demeter.ipan.lublin.pl 0016-706 I /96/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved PII SO0 16.706 I (96)00056-O