Effect of soil texture, organic carbon and water retention on the compactability of soils from the Argentinean pampas

The Mollisols from the Pampas Region of Argentina have been described as pr esenting different compactability behaviors under agricultural systems. The purpose of this study was to provide information on the inherent soil fact ors related to the susceptibility to compaction. Total organic carbon (TOC) , texture (CLAY, SILT, SAND), water retention at 0.33 kPa (WR), Proctor max imum bulk density (BDMAX) and critical water content (CWC) were determined for 26 top-soils selected from the semiarid, subhumid and humid Pampas Regi on. The selected sites crossed three soil textures (loamy sand, loam and si lty loam). It was observed that the compactability of these soils could be assessed by inherent properties routinely measured in the laboratory. Their behavior under experimental compaction revealed that TOC had a dominant ef fect on the susceptibility of these soils to compaction. Higher TOC levels reduced the BDMAX (r(2)=0.75, p<0.01) and the CWC (r(2)=0.82, p<0.01), inde pendently of textural class. The increase in BDMAX per unit of water conten t (susceptibility to compaction, SC) depends on SILT and TOC levels (r(2)=0 .49, p<0.01). Although the BDMAX levels were lower than those considered cr itical for rooting and diminished with increasing TOC, water and SILT conte nts, in addition to TOC, can determine the potential for compaction in thes e soils. Based on the need to prevent shallow compaction, continuous no-til l systems are possible on soils From the semiarid Pampas Region but not in soils from the subhumid and humid Pampas Region with low TOC. (C) 2000 Else vier Science B.V. All rights reserved.