Storage of hard seeded pasture legumes increases germination when sown in early autumn

Robert Harrison, Murdoch University

Background:

The expense of scarifying and dehulling of certain pasture legumes (e.g. yellow serradella) can be counterproductive to the adoption of pasture legumes in medium to low rainfall environments. Summer or twin sowing of hard seed is well known to bypass this barrier of adoption, however, not all pasture legumes have the hard seed breakdown pattern suitable for these sowing techniques. Notwithstanding this, the Centre for Rhizobium Studies has recently published an article describing the effect of storage on hard seed breakdown patterns (Harrison, et al., 2020).

Research abstract: Knowledge of the hard seed content of annual legumes, and its pattern of breakdown, is critical to the understanding of their ecology and management within farming and natural ecosystems. For logistical reasons, seed that has been stored for varying lengths of time is often used for pasture establishment and agronomy experiments. However, the implications of storage on hard seed physiology is unknown. The aim of this study was to explore the impact of seed storage on its subsequent pattern of hard seed breakdown

when exposed to field conditions. Experiments examined seed from six different annual legume genotypes that had been either produced the prior year or stored under ambient conditions for 11-22 years (two examples below, Figure 1 and 2). Comparisons were then made between the two seed sources on hard seed breakdown patterns in the soil. Although initial hard seed levels were mostly unaffected by storage (seed of five genotypes remained over 93% hard after more than 11 years of storage), the patterns of release from dormancy during exposure to hard seed breakdown conditions of stored seed differed greatly (p< 0.05) from freshly produced seed. Hard seed in the stored seed of most genotypes was reduced from > 90% to < 10% within 68 days over autumn, with shallow burial, whereas fresh seed remained > 90% hard during the same period.

Figure 1: (Top) Hardseed breakdown of both fresh and stored seed of M. littoralis x tornata cv. Toreador (seed in pod) exposed to field conditions over 129 days. 95% Confidence intervals are presented at the intersected points to represent significant difference.

Figure 2: (Bottom) Hardseed breakdown of both fresh and stored seed of T. spumosum exposed to field conditions over 129 days. 95% Confidence intervals are presented at the intersected points to represent significant difference.

Further research in 2020 has identified that the rate of germination as well as the hard seed breakdown pattern has both been accelerated. However, more pasture legume species need to be examined in the next season as well as the sowing time, so further recommendations can be made to farmers.

Paper reference for further reading: Harrison, Robert J., Howieson, John G., Yates, Ron J. and Nutt, Brad J. (2020) Long-term storage of forage legumes greatly alters the hardseed breakdown pattern in situ. Grass and Forage Science.