EVALUATION OF PASTURE LEGUMES SOWN INTO A PREPARED SEEDBED AT TAMWORTH, NEW-SOUTH-WALES .2. SEED PRODUCTION AND SEED RESERVES

Plots sown in 1983 were used to examine the seed production and reserv es (residual hardseeds) of 15 annual legumes over 5 years at Tamworth in northern New South Wales. Seed production characteristics were meas ured in 1983 for these annuals, and for 6 perennial legumes. After the annuals had set seed in 1983, an area of the plots was sprayed to pre vent flowering in subsequent years, and the rates of decline in seed r eserves were compared with those from areas that seeded annually. Seed yields of the perennials were often significantly lower than those of the annuals except Trifolium glomeratum. Seed yields of T. subterrane um var. subterraneum cvv. Seaton Park and Woogenellup were significant ly higher than those of cv. Nungarin and T subterraneum var. brachycal ycinum cv. Clare. Seed numbers were lowest for Medicago scutellata cv. Sava among the annual medics, and for Nungarin among subterranean clo vers. There was little relationship between the mean number of seeds p roduced from 1983-86 and maturity grading, and between seed numbers an d relative dry matter yield. Seed reserves decreased over 5 years by m ore than 90% in the sprayed treatments of all species. This decrease w as not continuous, with the largest declines occurring from December 1 983 to August 1984. In the sprayed treatments of Seaton Park, Woogenel lup, and Clare, and in both treatments of Astragalus hamosus cv. Ioman , Vicia dasycarpa var. villosa cv. Namoi, and T hirtum cv. Hykon, none of the original 1983 seed was recovered in 1987. For the annual medic s and Nungarin, the number of residual hardseeds in the sprayed treatm ents in 1987 was about 3-5% of the seed produced in 1983. From 1983 to 1987, seed numbers in the unsprayed treatments declined by 70-80% for the annual medics and by 85-95% for Seaton Park, Woogenellup, and Cla re. Long-term persistence of annual medics and Nungarin depended on se ed production in most years and the maintenance of a hi-h number of re sidual hardseeds in the soil. In contrast, the mid- and late-maturing subterranean clovers Woogenellup and Clare had low seed reserves and w ere dependent on seed production in most years for their continued reg eneration.