|Thomas, Andrew - MISSOURI BOTANICAL GARDEN|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 23, 1996
Publication Date: N/A
Interpretive Summary: Soil ridging, which is part of the ridge-till system, has been practiced for centuries, but little is known about its effect on corn root systems. Farmers and plant breeders need a better understanding of the effect of timing of ridging on corn root growth to maximize the production of ridge-till systems. The objective of this research was to determine the effect of timing of soil ridging on corn brace root growth and stem growth. In general, soil ridging increased the number of brace roots and the length of that part of the stem that was covered with soil during ridging. Ridging soil around the base of corn plants when less than six leaves have emerged tended to increase stem length. Earlier ridging did not increase the number of brace roots as much as ridging when the seventh leaf had emerged. Shoot dry weight and grain yield were not affected by time of ridging treatments. By increasing the number of brace roots, ridging when corn plants have seven leaves might be used by farmers to improve lodging and corn rootworm resistance. Because rootworm damage is usually restricted to the older roots, development of additional brace roots may allow corn plants to tolerate some rootworm damage. As a result, the need for insecticides might be reduced without reducing the productivity and profitability of ridge-till.
Technical Abstract: A greater understanding of maize nodal root response to soil ridging is needed to be able to maximize the benefits of ridge-till tillage systems. Field (two Iowa sites, 1992 and 1993) and greenhouse (three trials, 1992 to 1994) experiments were conducted to examine the effect of the time of soil ridging on maize nodal roots, 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 weights, 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 trail, 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. Stimulating development of functional roots at the upper rooting nodes may be important to maize plants in terms of lodging resistance and in recovery from corn rootworm damage.