The Anchorage Mechanics of Maize, Zea mays

The anchorage system of mature maize Zea mays was investigatedby combining morphological and anatomical study of the rootsystem with mechanical tests on roots and with studies in whichplants were pulled over. The root system is dominated by 20–30adventitious roots which emerge in rings from the stem basepointing radially downwards and outwards, approximately 30°from the vertical. Roots are strengthened near their base bya heavily lignified exodermis which makes them rigid in bending;distally, strength and rigidity both decrease because rootsbecome thinner and less lignified. When plants were pulled over,a maximum anchorage moment of 5–20 Nm was mobilized atangles of 8–10°, 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 leewardroots to axial motion through the soil and to bending. At displacementsover 10°, however, leeward roots buckled under combinedbending and compression and the centre of rotation shifted tothe windward perimeter of the root system; subsequent movementof the cone of roots and soil was resisted only by the bearingstrength of the soil beneath it. The differences between anchorage failure in balsam and sunflowersand that in maize probably results from the lower angular spreadand the weakness in compression of the maize roots which preventsthe leeward side of the root system from bearing large downwardloads. The system behaves more like that of wheat; these resultssuggest that the lodging resistance of both plants may be improvedby increasing the bending strength and angle of spread of theadventitious roots. Key words: Zea mays, roots, anchorage