| Abstract: | Abstract A tillage system, ‘slit‐till’, has been developed that modifies plowpans and permits root penetration and proliferation into subsoil horizons. Slit‐till also provides a means of placing nutrients into subsoil zones where roots are concentrated. Greenhouse studies determined the effects of calcium nitrate, calcium phosphate, ammonium phosphate, ammonium nitrate, and dolomitic limestone on grain sorghum Sorghum bicolor (L.) Moench] shoot and root development in a compacted layer of acid subsoil (pH 4.3), subject to a slit‐till treatment, and on chemical properties of soil adjacent to the injection site. Cylinders were prepared by layering A and B horizons of a Marvyn loamy sand (fine‐loamy, siliceous, thermic, Typic Hapludult) to form 56 cm of subsoil and 10 cm of topsoil in polyvinylchloride (PVC) tubing (20 × 66 cm). A 6‐cm‐thick hardpan (bulk density 1760 Mg.m‐3) was created at the top of the subsoil layer. The amendments, 500 μg/g of dolomitic limestone and 15 μg/g each of the other amendments, were injected into a 10 × 10 × 0.4 cm slit. Sorghum shoots and roots were harvested 49 days after plant emergence. Plant height was increased 15% by calcium nitrate, calcium phosphate, ammonium phosphate, and dolomitic limestone, but decreased 15% by ammonium nitrate. Twenty‐nine percent of the roots for the check occurred in the subsoil, but this increased to 49% with ammonium phosphate. Soil pH was increased and exchangeable aluminum was decreased by the dolomitic limestone up to 12 mm from point of injection. |
