Maize Nodal Root Response to Time of Soil Ridging

An improved understanding of maize ( Zea mays L.) nodal root response to soil ridging is needed to allow farmers to maximize the benefits of ridge‐till tillage systems. Greenhouse (three trials, 1992 to 1994) and field (two sites in Iowa, 1992 and 1993) experiments were conducted with one maize hybrid to examine the effect of time of soil ridging on nodal root development, internode elongation, shoot dry matter, and grain yield. Maize root clumps were evaluated from unridged plants and from plants ridged either at early V4 to V6) or late (V7) growth stages. Total numbers of nodal roots, numbers of roots per node, numbers of nodes developing functional roots, internode lengths, shoot dry matter, and grain yields (field study) were determined. Time of ridging significantly affected nodal root numbers and internode lengths. In two of the field trials, unridged maize plants produced 42.7 and 48.3 functional nodal roots, whereas plants ridged at growth stage V7 developed significantly more, 47.0 and 56.0 roots, respectively. Internodes 6 and 7, covered with soil during ridging, increased in length by as much as 124% in the field and 175% in the greenhouse when plants were ridged early rather than late. In one field trial, Internode 6 elongated to 44.1 mm with early ridging, but to less than 17.0 mm with either late or no ridging. Shoot dry matter and grain yields generally were not affected by ridging treatments in either field or greenhouse experiments. Later ridging tends to result in shorter internodes and more functional nodal roots which may be important to maize plants in terms of lodging resistance and recovery from corn rootworm ( Diabrotica spp.) damage.