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 presenting different compactability behaviors under agricultural systems. The purpose of this study was to provide information on the inherent soil factors related to the susceptibility to compaction. Total organic carbon (TOC), texture (CLAY, SILT, SAND), water retention at 0.33 kPa (WR), Proctor maximum bulk density (BDMAX) and critical water content (CWC) were determined for 26 top-soils selected from the semiarid, subhumid and humid Pampas Region. The selected sites crossed three soil textures (loamy sand, loam and silty 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 effect 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), independently of textural class. The increase in BDMAX per unit of water content (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 critical for rooting and diminished with increasing TOC, water and SILT contents, in addition to TOC, can determine the potential for compaction in these soils. Based on the need to prevent shallow compaction, continuous no-till 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 Elsevier Science B.V. All rights reserved.