Cone Index Values Diagnostic of Where Subsoiling Can Increase Corn Root Growth
- M.J. Vepraskas and
- M.G. Wagger
To identify root restrictive layers in a field using a penetrometer, a diagnostic cone index (CI) value indicative of restricted root growth must be known for the particular soil and crop. This investigation identified diagnostic CI values indicative of where corn (Zea mays L.) root abundance could be increased by subsoiling. Two tillage treatments were evaluated in seven Typic and Arenic Paleudults from 1985 through 1987. Penetrometer readings were made weekly in the plant row of both tillage treatments to a depth of 0.4 m. Roots were described primarily between 77 and 90 d after planting (DAP). Root observations were expressed on a proportional basis and were termed relative root abundance. Regression analyses showed that relative root abundance in the chiseled treatment was related to mean CI, depth, and clay percentage (R2 = 0.85). By 77 to 90 DAP, subsoiling significantly (P> 0.10) reduced mean CI as compared to the chiseled treatment at depths below 0.1 m, while significant increases in relative root abundance as a result of subsoiling were found primarily at 0.3 to 0.4 m. Diagnostic CI values for the chiseled treatment were identified where relative root abundance could be increased by subsoiling. Diagnostic CI values decreased with soil depth and increased with clay percentage. For a depth of 0.35 m, subsoiling was estimated to increase root abundance where the mean CI over a 3- to 5-wk period was greater than approximately 1.5, 3.0, and 4.5 MPa for soil layers having clay percentages of 4, 12, and 20%, respectively.
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