Crop yield response to precision deep tillage

Experimental precision deep tillage was applied at three sites in central Kentucky with relatively well-drained silt loam soils in no-till crop production. Fields were divided into 0.4 ha (1 ac) grid cells using DGPS mapping. Assessment of soil compaction by machinery traffic was made using multiple soil cone penetrometer measurements and expressed as cone index (CI). Corn, wheat, and soybean yields were depressed in grid cells with CIavg > 1.5 MPa (218 psi) prior to application of tillage treatments at sites 1 and 3, whereas at site 2, where most of the highest average CI values ranged from 1.44 to 1.49 MPa (209 to 216 psi), the opposite was true. In general, deep tillage resulted in yield improvement in compacted grid cells relative to those receiving no deep tillage; however, differences were significant at the 10% level in only two of six instances. Cells tilled to 40 cm generally had higher yields than cells tilled only to the depth at which CIavg > 1.5 MPa (218 psi) (precision deep tillage) at sites 1 and 3. However, the opposite was true for double-crop soybean subjected to limited rainfall. At site 2, tilled cells had higher yields than non-tilled cells, with precision tillage showing the maximum relative yield.