| Normal fall and spring tillage practices create poor physical conditions for crop growth on Charity clay (fine, illitic (calcareous), mesic Aeric Haplaquept). This soil has an unstable surface and poor internal drainage due to its naturally dense subsoil. Tillage studies were conducted from 1983 to 1985 to evaluate the potential for increasing crop yields by reducing the physical limitations of Charity clay and a second lake-plain soil, Parkhill loam (fine-loamy, mixed, nonacidic, mesic Mollic Haplaquept). Crops included in the study were dry bean, soybean, corn, sugarbeet, oat and winter wheat. Both soils were subsoiled and subsequent traffic was controlled to avoid recompaction of the loosened soil.;Subsoiling improved the physical condition of Charity clay below the Ap Horizon. Physical changes created by subsoiling persisted through only one crop year. Compaction caused by wheel traffic associated with conventional spring tillage was evident in the surface of Charity clay and below the normal depth of plowing. Fall moldboard plowing plus conventional spring tillage produced the least favorable conditions for crop growth in terms of soil aeration. Crop response to tillage depended on the climate each year and differed from one crop to another. Subsoiling tended to increase soybean and sugarbeet yields in 1983. Controlled traffic improved seedling emergence most of the time, increased dry bean rooting in 1983, and tended to increase crop yields.;Tillage effects on aeration of Charity clay were evaluated further using CERES-Maize, a daily-incrementing model of maize growth and development. This model was useful because the soil water balance is calculated on daily basis and soil inputs can be altered to account for varying soil conditions created by tillage. Air porosities corresponding to simulated water contents were used as the basis for calculation of cumulative stress day index (SDI), an indicator of soil aeration stress. Results of a long-term study using generated weather data, the CERES-Maize model, and the SDI approach suggest that poor aeration under conventional fall and spring tillage may limit yields on this soil during at least one of three years. |
