SEED PRODUCTION IN CLUSTER CLOVER (TRIFOLIUM-GLOMERATUM L.) 2 - EFFECT OF SOWING TIME AND SOWING RATE ON FLOWERING TIME, ABORTION, SEED SIZE, AND HARDSEEDEDNESS

An ecotype of cluster clover (Trifolium glomeratum L.) common to the w heatbelt of Western Australia was sown in pure undefoliated swards at rates in the range 2-256 kg/ha, on 2 dates to give growing seasons 13 and 18 weeks in length. Irrigation was phased out at the time of flowe ring of late-sown plots. The treatments generated a scale of seed prod uction in cluster clover from 148 kg/ha (43000 seeds/m(2)) to 1640 kg/ ha (389000 seeds/m2). Delayed sowing was more important in reducing se ed production than was increasing sowing rate. By comparison with the early-sown plots, the late-sown plots had less above-ground biomass at flowering (2053 v. 2728 kg/ha); 48-66% fewer inflorescences per m(2); a shorter vegetative phase (9 days); fewer seeds per inflorescence (2 6 v. 31); and lesser seed mass (337 mu g v. 436 mu g). There was littl e effect of the treatments on hardseededness except that hardseedednes s after 1 season in the field was higher in seeds from late-sown sward s at high sowing rate (58%) than from late-sown swards at low sowing r ate or early-sown swards (40%). Neither sowing rate nor sowing time in fluenced the within season pattern of hardseed breakdown. The results indicate that cluster clover is capable of massive seed production, an d that even under highly stressed conditions seed production is maximi sed by a high reproductive allocation and small seed size. Despite con ditions which reduced seed production by up to 90%, cluster clover is able to maintain its seed quality. Relatively few inviable seeds are p roduced and hardseededness is either unaffected or enhanced.