DEEP TILLAGE EFFECTS ON COMPACTED SURFACE-MINED LAND

Federal law requires that surface-mined prime farmland be reclaimed and restored to premining productivity for row crops (Surface Mining Control and Reclamation Act, Public Law 95-87). In Illinois, reclamation must include soil horizon replacement (topsoil and subsoil) to a depth of 120 cm. Poor physical condition is the most limiting factor in reclamation in Illinois. The effects of five deep tillage implements (80-120-cm tillage depth) and two standard agricultural chisel plows (20-35-cm tillage depth) were evaluated for 6 yr. The seven tillage treatments were applied to a scraper-placed minesoil that had a high soil strength (2.5-3.5 MPa) throughout the reconstructed profile. A nearby tract of undisturbed Cisne silt loam (fine, montmorillonitic, mesic Mollic Albaqualf) was used as a prime farmland comparison. Crop yields for both corn (Zea mays L.) and soybean [Glycine mar (L.) Merr.] significantly increased with tillage depth. Average soil strength decreased and net water extraction increased with increasing depth of tillage. The 1.2-m-deep tillage treatments significantly reduced average 23- to 114-cm soil strength from 2.8 to 0.93 MPa. Significant correlation occurred between 23- to 114-cm average soil strength and 6-yr mean corn (-0.97** [significant at P = 0.01]) and 4-yr mean soybean (-0.92**) yields. Deep tillage successfully restored productivity; however, the depth of tillage necessary was influenced by initial levels of soil strength.