THE ANCHORAGE MECHANICS OF MAIZE, ZEA-MAYS

The anchorage system of mature maize Zea mays was investigated by combining morphological and anatomical study of the root system with mechanical tests on roots and with studies in which plants were pulled over. The root system is dominated by 20-30 adventitious roots which emerge in rings from the stem base pointing radially downwards and outwards, approximately 30-degrees-C from the vertical. Roots are strengthened near their base by a heavily lignified exodermis which makes them rigid in bending; distally, strength and rigidity both decrease because roots become thinner and less lignified. When plants were pulled over, a maximum anchorage moment of 5-20 Nm was mobilized at angles of 8-10-degrees, larger plants having stronger anchorage. Movement was initially centred on the leeward side of the stem, anchorage being due to the resistance of both windward and leeward roots to axial motion through the soil and to bending. At displacements over 10-degrees, however, leeward roots buckled under combined bending and compression and the centre of rotation shifted to the windward perimeter of the root system; subsequent movement of the cone of roots and soil was resisted only by the bearing strength of the soil beneath it. The differences between anchorage failure in balsam and sunflowers and that in maize probably results from the lower angular spread and the weakness in compression of the maize roots which prevents the leeward side of the root system from bearing large downward loads. The system behaves more like that of wheat; these results suggest that the lodging resistance of both plants may be improved by increasing the bending strength and angle of spread of the adventitious roots.