MODIFIED NO-TILL SYSTEMS FOR CORN FOLLOWING WHEAT ON CLAY SOILS

Concerns about corn (Zea mays L.) grain yield reduction with no-till f ollowing winter wheat (Triticum aestivum L.) in rotation oil clay soil s has been a major factor in slowing the rate of adoption of no-till s ystems in Ontario. Our objective was to determine conservation tillage and wheat residue management systems that provide favorable seedbed c onditions for emergence, growth, and yield of corn following winter wh eat on clay soils. Seven tillage and residue management systems (fall moldboard plow, chisel plow, tandem disk, and zone-till, and no-till b are and with straw baled and not baled) were evaluated in 1994 and 199 5 at two locations in Ontario. Fall zone-till reduced the amount of wh eat residues on the soil surface. Wheat residues remaining in late fal l with zone-till, no-till (baled), and no-till (not baled) treatments were 3.1, 4.0, and 7.1 Mg ha(-1). Volumetric soil moisture levels in t he top 15 cm early in the season did not differ among fall tillage tre atments, but were all lower than for no-till with wheat residue. Modif ying the no-till system by adopting fall zone-till or fall tandem disk produced grain yields no different front fall moldboard plow or fall chisel plow treatments, and greater by 5 to 10% than for no-till with wheat residue. No-till yield potential was affected by the level of wh eat residue present. Completely removing all wheat residue increased n o-till corn grain yields by 0.5 and 0.9 Mg ha(-1) compared with baling and not baling straw, respectively. The baled and not-baled no-till t reatments had the lowest proportion of finer soil aggregates in the se edbed, greatest penetrometer resistance up to the 20-cm soil depth, sl owest corn growth, and lowest grain yield. We recommend zone-till or t andem disk in the fall for corn production on clay soils following whe at.