Hard seed breakdown patterns of serradella (Ornithopus spp.) in two contrasting environments of south-eastern Australia

ABSTRACT Context. There is interest in using serradella (Ornithopus spp.) in permanent pastures of the high rainfall zone of south-eastern Australia. However, there is little information concerning levels of hardseededness or patterns of seed softening in these environments. Aim. This study quantified seed softening of serradella species in comparison with subterranean clover (Trifolium subterraneum L.) in the Southern Tablelands and Central Slopes districts of eastern Australia. Methods. Mature seeds were placed in mesh pouches on the soil surface and were retrieved periodically to assess residual hard seed proportions throughout the growing season(s) in four experiments conducted over 2018 and 2019. Key results. Patterns of seed softening among adapted cultivars of subterranean clover were consistent: initially high proportions of hard seed, followed by rapid softening from mid-summer to the end of autumn with the remnant portion of seeds remaining hard. In contrast, diverse patterns of seed softening were observed among serradella cultivars, ranging from highly soft-seeded through to high initial hard seed portions that either softened rapidly or softened over a lengthy period. Rates of seed softening were faster in the warmer/drier environment of Cowra compared to the wetter/cooler environment of Canberra. Conclusions. The study revealed seed softening patterns among serradellas to be diverse and different to subterranean clover. This will affect management and suitability of serradella cultivars for permanent pastures. Implications. In permanent pastures, serradellas that soften slowly over several years are likely to have limited regeneration in the year after pasture establishment with a high potential for weed invasion.