Seed softening patterns from single seed crops of subterranean clover (Trifolium subterraneum L.) in a cool temperate environment

Abstract

An experiment was set up in northern Tasmania with 7 cultivars of subterranean clover widely ranging in maturity and levels of hardseededness. They were planted as pure swards and in a mixture with perennial ryegrass. After seed set in the first year, all seedling regenerations were counted and then killed, and seed populations were measured each summer for 6 years. No significant differences in seed losses existed between the pure swards and the mixtures or between cultivars. Negative exponential functions of the relationship between seed banks and time fitted the data well with r2 ranging from 0.87 (Nungarin) to 0.998 (Trikkala). By mid-summer of the sixth year the percentages of the original seed left in the ground were: Enfield 12%, Woogenellup 19%, Trikkala 20%, Nungarin 21%, Larisa 24%, and Karridale and Mt Barker 31%. Seeds at higher latitudes were lost at about half the rates experienced at lower latitudes with drier, hotter summers. The higher percentages of seed remaining in plots with later maturing cultivars suggest that environmental conditions favoured the production of hard seeds while the reverse was the case with very early, hardseeded cultivars like Nungarin.