Estimates of subterranean clover flowering time in New Zealand

Abstract Subterranean clover ( Trifolium subterraneum ) is a legume suitable for summer dry environments in New Zealand where rainfall is <900 mm/year. However, limited knowledge of phenology of different commercially available cultivars of subterranean clover, particularly flowering time, currently restricts the development of best management practices that optimise vegetative plant growth while also ensuring adequate seed set under different environments. In a field study, four commercial, Australian cultivars (‘Antas,’ ‘Denmark,’ ‘Leura’ and ‘Woogenellup’) were compared for flowering time across sowing dates. For each cultivar, the number of days to flower decreased around 30% from 215 days as the sowing date was delayed from February to May. The thermal time to flowering averaged 1944 ± 102 o Cd, or approximately 600 o Cd longer than found for Australia. Flowering time was positively related ( R 2 = 0.97) to temperature and modified by the photoperiod duration and direction. A model and historical weather data were used to predict flowering and grazing periods (GPs) for two New Zealand locations (i) Lincoln (South Island) and (ii) Hastings (North Island). Four establishment times (February–May) were considered based on the time of opening rains and the ‘safe graze’ start time. For both locations, an early subterranean clover establishment on 1 February provided the longest GP, up to 217 ± 13 days in Lincoln and 172 ± 8 days in Hastings. At Lincoln, the GP was on average 34 days longer than in Hastings because of the later flowering time. The plant establishment in May resulted in the shortest GP, 122 ± 8 days in Lincoln and 104 ± 6 days in Hastings. The coefficients calculated should allow specific dryland management strategies to be tailored for different environments to optimise the time of grazing, but still allow subterranean clover to flower and seed set.