TEMPERATURE AND SOIL-WATER EFFECTS ON DORMANCY AND MORTALITY OF SUBTERRANEAN CLOVER SEED

Germination tests were conducted to investigate possible causes for a reestablishment failure of subterranean clover (Trifolium subterraneum L.). 'Mount Barker' subterranean clover seeds were germinated on blotters and on the soil surface or at 1 cm depth in nonfumigated and fumigated soil at four constant temperatures for 14 d, followed by constant 15 degrees C for 8 d. Fumigation had no effect on germination. Germination on blotters was reduced to <11.1% at 25 and 30 degrees C, compared with 94.5% at 15 degrees C. Emergence of seedlings was reduced to 37.9% at 30 degrees C, compared with 92.5% at 15 degrees C. Emergence of seedlings at 30 degrees C from soil was greater after 14 d than germination on blotters. In a second experiment, seeds buried 1 cm were germinated at soil water levels ranging from 0.0 to 0.816 kg kg(-1). Temperatures were 15 or 30 degrees C for 7 d, then 15 degrees C for 7 d more. Seeds failed to germinate at either temperature in dry or saturated soil. Emergence after 7 d was reduced at 30 degrees C compared with 15 degrees C at soil moisture levels from 0.204 to 0.544 kg kg(-1). After 7 more d at 15 degrees C, emergence was similar between temperatures at soil moisture levels from 0.0 to 0.544 kg kg(-1). Under saturated soil conditions, 28.5 and 80.8% of the seed rotted at 15 and 30 degrees C, respectively. Our results suggest that subterranean clover seeds can survive in pasture soil for 14 d in an embryo dormant condition during the summer, unless the soil is saturated, in which case soft seeds tend to decay.