Tillage‐Enhanced Argillic Horizon Development in Piedmont Soils

The soils of the Piedmont physiographic province of southeastern Pennsylvania are typically deep Ultisols and Alfisols with well‐developed argillic horizons, formed from metamorphic and igneous bedrock. Much of the research on the development of these argillic horizons focuses on descriptions of the soils in the field. This study was conducted to determine whether the act of tillage may mobilize clays within the solum and facilitate translocation of these clays, thereby enriching the argillic horizons with colloids. Most of this region has been subjected to long‐term, intensive agriculture. Anecdotal evidence and experience indicate that argillic horizons in agricultural fields appear to be deeper, are richer in clays, and exhibit lower porosities and permeabilities than similar soils in adjacent landscapes under forest cover. Two soil columns were constructed with a simple Entisol model of a silty clay loam “A” horizon over a coarse sand “C” horizon. The columns were subjected to identical moisture regimes by ponding 2.5 cm of water at the surface 184 times during a 1‐yr period. One column was plowed before application of water. The columns were then dissected for further observation. Slides were collected from points within the columns and examined using both optical and scanning electron microscopy. The plowed column appeared to exhibit much higher clay translocation, both in mass and depth of translocation, than the unplowed column. The plowed column appeared to have obvious clay translocation to a depth of 8 cm as opposed to 4.2 cm for the unplowed and exhibited distinct clay coatings on sand grains and clay bridging between grains. This indicates that agricultural practices may contribute greatly to the formation and thickening of argillic horizons.