FACTORS CONTRIBUTING TO THE LOSS OF SEED FROM THE SEED-BANK OF TRIFOLIUM-BALANSAE AND TRIFOLIUM-RESUPINATUM OVER SUMMER

The influence of predation, fungi and germination of seed of the annua l legumes Trifolium balansae and Trifolium resupinatum was investigate d by placing known quantities of seed in bags in the field; combinatio ns of all three factors were imposed. It was found that rainfall was t he most important factor contributing to the loss of seed over summer (up to 76%), followed by predation (up to 15%); fungi had only a very small influence (0.1-0.2%). Predation contributed to a larger percenta ge of loss over summer in T. resupinatum line SA14433 than in T. balan sae cv. Paradana, which is attributed to seed size. The effect of summ er grazing on the size of the seed-bank was investigated. It was found that summer grazing did not influence the amount of seed present in t he seed-bank in March. Removal of all surface material in December res ulted in a significant drop in seed reserves compared with the ungraze d or grazed areas. Hardseededness in March was not affected by any of the treatments; the seedling density after regeneration was not affect ed by summer grazing, but was reduced when all surface material was re moved. The data were incorporated in a model to describe seed loss fro m the seed bank over summer quantitatively; the utility of such models is discussed.