Dormancy and longevity of annual ryegrass ('Lolium rigidum') as affected by soil type, depth, rainfall, and duration of burial

Effects of soil type, time, depth of seed burial and rainfall pattern were investigated on the longevity of glyphosate resistant annual ryegrass ('Lolium rigidum' Gaudin) in the northern summer rainfall dominant grain region of Australia in a 16 month experiment conducted under polyhouse conditions. 'Lolium rigidum' seeds placed in nylon bags were buried in pots at 5 and 10 cm depth in either Laureldale (clay) or Kirby (sandy loam) soil receiving simulated rainfall representing a Tamworth (summer) and Hamilton (winter) rainfall environment of Australia. The bags were exhumed every four months and tested for percent viable, germinable, dormant and dead seeds. In the short term (several months), factors such as soil type, rainfall and depth of burial affected the fate and condition of 'L. rigidum' seeds and emergence pattern of seedlings. However, irrespective of treatment, all seeds lost their viability after 16 months of burial. Hence, in the longer term, 'L. rigidum' behaviour in this summer dominant rainfall environment with different soils is likely to be similar to that where the weed occurs more commonly in the southern Mediterranean regions of Australia. Maximum emergence in the polyhouse occurred during mid autumn similar to that in the field. The results from this experiment will allow for the development of management strategies which may enhance the depletion of the soil seedbank of viable 'L. rigidum' seeds in the shortest possible time.