Seed production in cluster clover (Trifolium glomeratum L.). 2. Effect of sowing time and sowing rate on flowering time, abortion, seed size, and hardseededness Smith, F.P.; Cocks, P.S.; Ewing, M.A. Australian Journal of Agricultural Research 49(6): 965-971 1998 https://eurekamag.com/research/003/267/003267675.php