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.

Legume persistence for grasslands in tableland environments of south-eastern Australia

“…From the network of Series 2 experiments reported here, along with other data from the same project (Boschma et al . 2019; Newell et al . 2023, in press), it is possible to assess the traits that may be influencing the relative performance of serradella cultivars compared with the best-performing subterranean clover cultivar, Goulburn (Table 7).…”

“…A potential limitation to the use of cv. Avila in grasslands is its relatively high level of hard seed and very slow pattern of hard-seed breakdown (Newell et al . 2023, in press), which results in lower second-year regeneration from the soil seed reserves than occurs with cultivars such as Yellotas.…”

“…Yellotas yellow serradella also compared favourably for the key morphological traits summarised in Table 7 and recorded the highest final frequency after 4 or 5 years at the Yass and Middle Arm sites. In contrast to Avila yellow serradella, Yellotas has a pattern of relatively rapid hard-seed breakdown (Newell et al . 2023, in press).…”

“…This resembles, somewhat, the pattern of hard-seed breakdown of many subterranean clover cultivars in these environments, although unlike subterranean clover, seed of cv. Yellotas continues to break down over winter to leave very low levels of residual hard seed at the beginning of the second year (Newell et al . 2023, in press).…”

“…In the case of subterranean clover, this involves multiple traits including the appropriate phenology to flower and set seed in a given environment before soil water is depleted. In addition, hard seed provides protection from germination at inappropriate times of year (Taylor 2005), and appropriate patterns of hard-seed breakdown enable germination when conditions are likely to be more favourable (Newell et al . 2023, in press).…”