Tillage as a Mechanism for Enhancement of Clay Translocation and Argillic Horizon Development.

The soils of the Piedmont region of southeastern Pennsylvania exhibit moderate to deep well developed argillic horizons. The soils are typically deep ultisols and alfisols formed from crystalline bedrock. Much of the research on the development of these argillic horizons focuses on descriptions of the soils in the field. This study was undertaken to determine whether the act of tillage may mobilize clays within the solum and facilitate translocation of these clays, thereby enriching the argillic horizons in colloids. Most of the area has been under long-term intensive agriculture. Anecdotal evidence and experience indicate that argillic horizons in agricultural fields appear to be deeper, richer in clays and exhibit lower porosities and permeabilities than in similar soils in adjacent landscapes under forest cover.

 Two columns, 30 cm x 60 cm x 9 cm, were constructed with a simple entisol model of a silty clayloam “A” horizon over a coarse sand “C” horizon. Over the course of a year, the columns were subjected to identical moisture regimes with 2.5 cm of water at a time being ponded on the surface and allowed to percolate through the column. One column was “plowed” 152 times, prior to introduction of water, the other was not. The columns were then deconstructed and examined. Slides were made of sampling points within the columns and examined using both optical and scanning electron microscopes. The “plowed” column appeared to exhibit significantly 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 significantly to the formation and thickening of argillic horizons.