THE MECHANICS OF ROOT LODGING IN WINTER-WHEAT, TRITICUM-AESTIVUM L

The anchorage of winter wheat, Triticum aestivum L., is provided by a cone of rigid coronal roots which emerge from around the stem base. During root lodging this cone rotates at its windward edge below the soil surface, the soil inside the cone moving as a block and compressing the soil beneath. A theoretical model of anchorage suggested that lodging resistance should be dependent on the diameter of the root-soil cone, coronal root bending strength and soil shear strength. We tested the predictions of the anchorage model by carrying out two series of experiments. In the first, varieties of contrasting lodging resistances were artificially lodged. The moment required to rotate plants into the soil, the diameter of the root-soil cone, and the bending strength of the coronal roots were recorded. The lodging moment was correlated with the size of the soil cone, as predicted. Generally, differences in anchorage strength between varieties were due to differences in root-soil cone diameter, although coronal root strength was also important. A second series of tests was carried out using model plants anchored by plastic discs. The behaviour of the models during artificial lodging supported the anchorage model; the force resisting lodging was similar to that of plants with root-soil cones of the same size and the resisting force was dependent on the soil strength. These results suggest that root lodging resistance might be improved by increasing both the angle of spread and the bending strength of the coronal roots.