Leaf appearance of annual clovers responds to photoperiod at emergence

• We generated thermal time models from field and controlled environment experiments to quantify leaf appearance rate of arrowleaf, balansa, gland and Persian clovers.
• We found that the leaf appearance rate was affected by the changes in duration and direction of photoperiod at seedling emergence.
• Autumn sown crops which emerged into shortening daylength took longer time to produce a leaf. In contrast, when crops emerged after the shortest day, into an increasing photoperiod, the leaf production rate was accelerated.
• The discrepancy in time to branch initiation was caused by the differences in phyllochron at sowing.
• We recommend that annual clovers should be sown in late summer or early autumn to maximize dry matter production.

Leaf appearance rate and time to canopy expansion of four annual clover species (arrowleaf, balansa, gland and Persian) were quantified in field and controlled environment studies. Crops sown in autumn, which experienced shortening daylengths at emergence, had a slower rate of leaf production and consequently took a longer time to initiate branching, than spring-sown crops. When autumn-sown ‘Bolta’ balansa clover emerged on the shortest day in winter (21 June), the rate of leaf appearance was lengthened by 4 °C d/leaf/h. When the same species emerged after the shortest day, into an increasing photoperiod, the phyllochron was shortened by 5 °C d/leaf/h. This influence of photoperiod on the phyllochron consequently altered the time to axillary leaf production (branching). Throughout all sowing dates, phyllochron was the fastest for ‘Prima’ gland (33–91 °C d/leaf) and slowest for ‘Cefalu’ arrowleaf (53–116 °C d/leaf) clovers. ‘Bolta’ balansa was 44–82 °C d/leaf and ‘Mihi’ Persian 61–93 °C d/leaf. The response of phyllochron to photoperiod suggests these annual clovers should be sown in late summer or early autumn to initiate axillary leaf production as soon as possible to ensure maximize dry matter for early spring.