Application of S – Theory to Evaluate the Effects of Tillage and Cover Crops On Soil Quality.

Data are presented from a 3-year experimental farmland management research project conducted at Penn State's experimental agriculture facility at Rock Springs, PA. A three-year rotation was established in the experimental fields with a cover crop in year 1, soybeans in year 2, and maize in year 3. This project followed a 2 x 2 factorial design, in which two tillage levels (full with moldboard plowing vs. minimum with non-inversion chisel plowing) are crossed with two year-1 cover cropping strategies (perennial cover with a timothy grass-oat-red clover mixture vs. annual cover with a rye-vetch sequence). There was a crop rotation contrast in only the first rotation year, as all fields were soy and corn in years 2 and 3, respectively. The tillage contrast was followed for all three rotation years. Each of the four treatments was replicated in four plots, so the experimental field comprised 16 plots, each approx 25 x 27 m. The entire experiment was initiated twice, in back-to-back years in adjacent fields (thus yielding a total of 32 plots, 16 per "start"). The "Start 1" field was first prepared in autumn 2003, with the three rotation years running 2004-06. "Start 2" was offset one year later.

Soils were sampled on two occasions for moisture retention determination, bulk density, aggregate stability, and hydraulic conductivity. The first occasion was following rotation year 1, while the second was after rotation year 3. In each plot on each sample date, one or two random locations were chosen for soil core sampling. At each locale, an intact soil core was collected from each of three depth horizons, 0-10, 10-20, and 20-30 cm. Soil cores were then returned to the lab in the Dept of Crop and Soil Sciences at Penn State, and moisture retention analysis was conducted. Soil volumetric water content was determined using intact cores for saturated soil, for soil subjected on a tension table to -10, -30, -50, -70, and -90 cm pressure, and for soil subjected in pressure plates to -0.33, -1, -3, and -15 bar pressure.

Preliminary results indicate that there is an effect of tillage on the S-value in the surface soil (0-10 cm), but not at depth (10-20 and 20-30 cm). Interestingly, there is a very strong effect of year-1 cover crop (steeper S with timothy than with rye) in the 20-30 cm range. This is fascinating because the cover crop contrast was only applied in year 1 (all plots were soy and maize in yrs 2 and 3), whereas these moisture retention data were collected at the end of year 3. So that means that there is a cover crop effect on “S” at depth 2 years after the cover crops were removed, even with full tillage.

Also, cover crop appears to affect the depth profile of S. Under rye, there is not much change with depth. For timothy, however, S grows steeper as you go deeper, regardless of tillage. These are fascinating results, because if these hold out with other subsets of the data from this project (coming soon), then these would be the strongest cover crop effects. Other soil biogeochemical measures (P, base cations, org C, aggregate stability) did not seem to be affected by cover crop.