RESIDUAL EFFECTS OF SLIT TILLAGE AND SUBSOILING IN A HARDPAN SOIL

Subsoiling and slit tillage can increase root growth through subsurfac e hardpans. In-row subsoiling fractures a section of the pan below the row. Slit tillage cuts a 3-mm-wide slit through the pan with a thin b lade mounted on a shallow subsoil shank, Subsoiling is usually repeate d annually, Slit tillage has been reported as an alternative to subsoi ling that does not need to be repeated annually. This study was conduc ted to determine the longevity of the effects of tillage on a fine loa my Acrisol at Florence, South Carolina, USA. Corn (Zea mays) root grow th, yield, and soil cone index were measured for 3 years in plots that had been slit tilled, in-row subsoiled, or no-tilled for 4 years imme diately prior to the study. During the study, no plots were tilled. Th ree-year average corn yields were 5.08 Mg ha(-1) for residual slit-til led treatments, 5.34 Mg ha(-1) for residual subsoiled treatments, and 5.07 Mg ha(-1) for the no-tilled treatments. Three-year mean profile c one indices were 2.53 MPa for residual slit-tilled treatments, 2.51 MP a for residual subsoiled treatments and 2.61 MPa for no-tilled treatme nts. Only 10% of the slits could be found 3 years after tillage, The l ack of persistence of the slits was a result of either slit infilling with sand from the Ap horizon or collapse of the slit walls. Roots gre w to a depth of at least 0.95 m in all treatments. Root growth was not correlated with yield. In this soil, residual subsoiled treatments ga ve higher yields than no-tillage treatments, but residual slit tillage did not. If deep tillage is not performed annually, subsoiling would be better than not tilling, but slit tillage would not.