Longevity of soil based seeds of Onopordum illyricum

C.J. AllanA and P.J. HolstB

A NSW Agriculture, Agricultural Research and Veterinary Centre, Forest Road, Orange, New South Wales 2800, Australia.

B NSW Agriculture, Agricultural Research Station, Cowra, New South Wales 2794, Australia.


Seeding was prevented for eight years, in a paddock containing a dense population of Onopordum illyricum, initiallyby grazing with mature bush goats for five years, then by chemical/mechanical means. The population of residual soil based seeds was monitored annually following autumn germination. Initially the soil based seed population was estimated to be 5 million seeds per hectare. After four years of seeding prevention, the soil based seed population decreased to 1.6 million seeds per hectare and maintained a steady state at that level. Seedling counts following germination reflect the decline in population of soil based seeds. After five years of seeding prevention in a 2.8 hectare paddock the area was reduced to 0.5 hectare. Within two years of no seeding control the soil based seed population in the foregone 2.3 hectares increased to levels commensurate with the population when monitoring began. Plant counts after seven years were 0.05 and 9 plants m-2 in goat and 'no-control' (sheep grazed) paddocks respectively.


Plant Protection Quarterly (1996) 11 (Supplement 2) 242.