SEED VIABILITY AND DORMANCY OF 17 WEED SPECIES AFTER 9.7 YEARS OF BURIAL IN ALASKA

A 50-year study at Fairbanks, AK, was started in 1984 to determine soi l seed longevity of 17 weed species. Seed were buried in mesh bags 2 a nd 15 cm deep and were exhumed 0.7, 1.7, 2.7, 3.7, 4.7, 6.7, and 9.7 y r later. Viability was determined by germination and tetrazolium tests . All common hempnettle and quackgrass seed were dead after 2.7 and 3. 7 yr, respectively. Less than 1% of wild oats and foxtaill barley seed were viable after 3.7 yr, but > 6.7 yr were required for loss of all viability. By 9.7 yr, < 1% seed viability remained for: bluejoint reed grass, corn spurry, pineappleweed, prostrate knotweed, and wild buckwh eat. From 2 to 5% of seed from common chickweed, common lambsquarters, flixweed, Pennsylvania smartweed, rough cinquefoil, marsh yellow-cres s and shepherd's-purse were viable, while 62% of American dragonhead s eed was still alive. Seed longevity in agricultural fields is not grea ter under subarctic conditions than under warmer conditions.