Crop growth and development affect seasonal priorities for lucerne management

Successful lucerne stand management requires balancing animal and plant requirements to produce crops of high quality and yield at times of high animal demand. Understanding the impact of environmental signals on crop growth and development can aid management decisions throughout the season. In spring, crops remobilise reserves from the roots to shoots and expand nodes accumulated through the winter, producing rapid stem extension and canopy closure as temperatures increase. The timing of spring defoliation should be based on crop yield and animal requirements rather than any specific developmental stage. Through spring and summer, crops should be rotationally grazed, with highest lamb live-weights achieved from 6-8 weeks grazing solely on lucerne. Summer crop production is dependent on rainfall and the plant available water content. During summer, grazing at the appearance of open flowers or basal buds is recommended as a compromise between maximum yield and quality. In autumn, the priority of assimilates allocation in the crop changes from above to below ground growth. To enhance the recharge of root reserves, an extended period of flowering is recommended in February or March. The time of flowering is dependent on the accumulation of thermal time and increases as photoperiod shortens. In periods of prolonged drought, lucerne herbage should be hard grazed and then spelled until the end of late autumn regrowth. A final hard grazing in June or early July, to remove overwintering aphids, should be followed by spraying 7-14 days later. Crops continue to develop nodes through the winter, and stands should be spelled until spring to ensure nodes are not removed by grazing, as this delays regrowth and reduces dry matter production. Key words: Flowering, grazing, herbicide, Medicago sativa, nodes, photoperiod, phyllochron, root reserves