HERBAGE PRODUCTION AND SEED YIELD OF DEFOLIATED SUBTERRANEAN CLOVER SWARDS IN A COOL TEMPERATE ENVIRONMENT

Seasonal growth patterns were determined for defoliated swards of 3 mid-season subterranean clover [Trifolium subterraneum] cultivars (Seaton Park, Woogenellup and Mount Barker) and 1 early-flowering cultivar (Nungarin) established at 3 times of the year (early March, mid-April, late May) in a cool tableland environment [Southeastern Australia]. The time of sowing significantly affected in the autumn, winter, spring and total herbage production of all cultivars. Swards sown in early March showed an autumn and spring peak in herbage with a depression in winter. Swards sown in mid-April or late May produced very little herbage in autumn and winter. Total herbage production ranged from 10.3 t/ha from a mid-season cultivar sown in early March to 3.2 t/ha from an early maturing cultivar sown in late May. Total herbage production of the mid-season cultivars was not related to maturity rating. ''Nungarin'', produced considerably (46-65%) less herbage than the mid-season cultivars. Its productivity was also the most sensitive to a delayed start to the growing season. The interval between sowing and flowering was shortened by later sowing, later maturing cultivars showing the greatest decrease. Seed yields ranged from 290 kg/ha for a ''Mount Barker'' sward (sown in late May) to 1203 kg/ha for a ''Seaton Park'' sward. On average, ''Seaton Park'' and ''Nungarin'' produced the highest seed yields, a result of setting more seed but not larger seed. ''Woogenellup'' set significantly larger seed than the other cultivars. Earlier maturing cultivars had the highest seed yields and appeared relatively insensitive to low temperatures during flowering. The use of early maturing cultivars in this environment could substantially reduce potential pasture production. ''Seaton Park'' was considered to be the most suitable cultivar, combining a high seed yield with good herbage production.