Estimation of time to key phenological stages to guide management of subterranean clover (Trifolium subterraneum L.) in New Zealand

Coefficients that describe phenological development of subterranean (sub) clover (Trifolium subterraneaum L.) were derived from field and controlled environment experiments. These were combined with national scale historical climate data to estimate when key stages in the life cycle occur at different locations in New Zealand. Based on a 20 mm accumulated rainfall threshold in autumn, sub clover germination and emergence in eastern regions of the South and North Islands occurred between 10th and 24th March and later (~ 31st March) in the cooler southern areas of the South Island, after 36 ± 6.0°Cd and 115 ± 9.0°Cd, respectively. During this time the absolute photoperiod decreases from 13.7 h to 11.6 h (at latitude −34.3950) and from 14.4 h to 11.1 h (at latitude-47.2590). In spring, flowering was estimated to commence in August in North Island locations but from September onwards in South Island locations. The group of cultivars classified as ‘Late’ flowering by plant breeders were estimated to flower in the North Island starting by mid-August compared with mid-September to mid-October in southern (cooler) regions. The safe grazing period was estimated as 25% longer for ‘Late’ cultivars than the ‘Early’ cultivars. The quantification of these key phenophases can be extrapolated to different regions to enhance strategic management of weed control, grazing times and closing dates for seed set. This should enable increased species persistence of sub clover in pasture swards.