DEEP TILLAGE EFFECTS ON COMPACTED SURFACE-MINED LAND

Federal law requires that surface-mined prime farmland be reclaimed an d restored to premining productivity for row crops (Surface Mining Con trol 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 rec lamation in Illinois. The effects of five deep tillage implements (80- 120-cm tillage depth) and two standard agricultural chisel plows (20-3 5-cm tillage depth) were evaluated for 6 yr. The seven tillage treatme nts were applied to a scraper-placed minesoil that had a high soil str ength (2.5-3.5 MPa) throughout the reconstructed profile. A nearby tra ct of undisturbed Cisne silt loam (fine, montmorillonitic, mesic Molli c Albaqualf) was used as a prime farmland comparison. Crop yields for both corn (Zea mays L.) and soybean [Glycine mar (L.) Merr.] significa ntly 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 occurr ed 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 .