Hardseededness and the pattern of softening in Biserrula pelecinus L., Ornithopus compressus L., and Trifolium subterraneum L. seeds

Abstract

Experiments measuring seed bank size, hardseededness, and seed softening of biserrula (Biserrula pelecinus L.) were conducted at Merredin and Perth in Western Australia. At Merredin, a mixture of 2 biserrula accessions was grazed, shallow cultivated, or left uncultivated and ungrazed. Seed bank size, seedling regeneration, and seed softening were measured over 2 years. At Perth, softening of biserrula, yellow serradella, and subterranean clover seeds grown at 2 sites (Binnu and Northam) was compared on the soil surface and after burial at 2 and 10 cm over a period of 2 years. Seed bank size of biserrula at Merredin ranged from 14000 to 17500 seeds/m2. Regeneration was greater in the second year (800–1700 seedlings/m2) than in the first year (40–600 seedlings/m2). In both years the shallow cultivated treatment recorded the highest number of seedlings. About 90% of biserrula and serradella seed remained hard after 2 years on the soil surface, compared with only about 10% of subterranean clover. Serradella softened more rapidly when buried 2 cm below the soil surface (8–12% hard) than it did on the soil surface (84–92% hard) (P<0.05). In contrast, the softening of subterranean clover decreased with increasing depth. Biserrula was intermediate, although it too softened most rapidly at 2 cm (78–95% hard compared with 82–97% on the surface) (P<0.05). Rate of seed softening in all species decreased with increasing depth of burial below 2 cm. Of the 4 accessions of biserrula, an accession from Greece (83% hard after 2 years exposure) was significantly softer than the other accessions. The results indicate that biserrula is very hardseeded, although there is sufficient variation in hardseededness for the selection of somewhat softer lines. Its pattern of softening suggests that biserrula may be successful in the ley farming system (crop/pasture rotations) of southern Australia.