A 50-year study at Fairbanks, AK, was started in 1984 to determine soil seed longevity of 17 weed species. Seed were buried in mesh bags 2 and 15 cm deep and were exhumed 0.7, 1.7, 2.7, 3.7, 4.7, 6.7, and 9.7 yr 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 foxtail 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 reedgrass, corn spurry, pineappleweed, prostrate knotweed, and wild buckwheat From 2 to 5% of seed from common chickweed, common lambsquarters, flixweed, Pennsylvania smartweed, rough cinquefoil, marsh yellow-cress and shepherd's-purse were viable, while 62% of American dragonhead seed was still alive. Seed longevity in agricultural fields is not greater under subarctic conditions than under warmer conditions.

A scentless plant bug feeds on velvetleaf seeds. Fungi, dominated by the genera Fusarium and Alternaria, were isolated from insect-attacked seeds at levels related to insect density on the plants. The combined effects of insect feeding and fungal infection decreased seed germination. Burial of insect-attacked seeds in soil for 24 months reduced seed survival and increased Fusarium infection. Decreases in velvetleaf seed viability and survival in soil caused by a seed-feeding insect and associated seed fungi suggests that subsequent infestations by velvetleaf can be decreased through integrated use of the two biological control agents.

Seed of 17 weed species that were buried at 2 and 15 cm at Fairbanks, AK, in 1984 were exhumed at 1-yr intervals and tested for germination and viability. Burial depth had a significant effect on seed viability of wild oats, bluejoint reedgrass, quackgrass, prostrate knotweed, and corn spurry with viability remaining higher at 15 than at 2 cm. The percent of viable foxtail barley and quackgrass seed that were dormant was greater at 15 than at 2 cm. Eleven of 17 species had greater than 6% seed viability 4.7 yr after burial. American dragonhead seed viability in 1989 was not significantly lower than in 1984. In contrast, viability of common hempnettle and quackgrass had dropped to zero by 2.7 and 3.7 years after burial, respectively. Foxtail barley and wild oats had less than 1% viable seed at the end of 4.7 yr. For most of the 17 species, a rectangular hyperbola model accounted for more of the variability in seed viability decline with time than did a negative logarithmic model.

Seedbanks and seedling emergence of annual weeds were examined in arable fields at eight locations in the Corn Belt. Seed densities were estimated by direct seed extraction from each of several soil cores in each sampled plot. Average total seedbank densities ranged from 600 to 162 000 viable seed m-2 among locations. Coefficients of variation (CV) typically exceeded 50%. CV for seed densities of individual species usually exceeded 100%, indicating strongly aggregated distributions. CV were lower for species with dense seed populations than those with sparse seed populations. Variance of total seedbank densities was unstable when < 10 cores were examined per plot, but stabilized at all locations when ≥ 15 cores were analyzed, despite a 12-fold difference in plot size and 270-fold difference in seed density among locations. Percentage viable seed that emerged as seedlings in field plots ranged from < 1% for yellow rocket to 30% for giant foxtail. Redroot pigweed and common lambsquarters were the most frequently encountered species. Emergence percentages of these species were related inversely to rainfall or air temperatures in April or May, presumably because anoxia and/or high temperatures induced secondary dormancy in nondormant seed. From 50 to 90% of total seed in the seedbank were dead. This information can be employed by bioeconomic weed management models, which currently use coarse estimates of emergence percentages to customize recommendations for weed control.

Accurate prediction of potential weed seedling density would allow growers to implement control measures more effectively and could help avoid inappropriate and over application of preemergence herbicides. We compared three methods for handling soil samples to predict potential weed seedling emergence in plow-disk and no-tillage corn: seedling emergence from greenhouse trays, emergence from intact cores, and seed extraction following sieving. Seedbank numbers were highest for common lambsquarters followed by annual grasses and redroot pigweed, and seed numbers were higher in no-tillage than plow-disk plots. Coefficients of variation typically exceeded 60%. Density of seedling emergence from cores was more similar to field density than was emergence from trays. The percent of seeds in the seedbank that emerged was commonly more than 90% for annual grasses and usually less than 20% for common lambsquarters. All methods gave equivalent and relatively poor predictions of field population density. Spearman rank correlation between predicted and actual populations ranged from low negative values for common lambsquarters in no-tillage to 0.60 for annual grass emergence from trays in 1991. No method consistently gave highest correlations in both years and both tillage systems. Seedling emergence from intact cores, evaluated for 4 yr in plow-disk and no-tillage soybean fields, was significantly correlated (rs = 0.15 to 0.68) with emergence in the field. Pooling data from three to five neighboring sample sites increased the correlation between core and field emergence densities.

Relationships among weed seed rain, soil seedbank, and seedling recruitment in no-tillage systems were studied from July 1993 to May 1996. Multiple regression analysis indicated that seedling recruitment of only six of the 25 weed species present was correlated with seed rain samples from the previous autumn, spring soil seedbank samples, or a combination of the two. However, seedling recruitment of the dominant annual grasses (yellow foxtail, giant foxtail, and fall panicum in Field 1–1994, Field 2–1995, and Field 3–1996, respectively) was related to seedbank populations or a combination of seedbank and seed rain densities. These grasses accounted for at least 32% of the emerged seedlings, 12 to 78% of the seedbank, and 16 to 77% of the seed rain. Seedling recruitment of large crabgrass and two broadleaf species, Virginia copperleaf and wild carrot, also were described by seedbank densities or a combination of seedbank and seed rain densities. However, both the broadleaf species were minor components of the cropping system, representing ≤ 4% of all seedlings. In each year, the sum of all weeds in the seedbank exceeded 1,300 seeds m−2 (0 to 10 cm deep). The fraction of the total seedbank that emerged each year ranged from 3 to 17%, but there was great variability among species. The aforementioned dominant grasses ranged in emergence from 3 to 25% of their seedbanks. Emergence of other species ranged from a low of 1% for common lambsquarters up to 41% for large crabgrass. Prediction of seedling recruitment from seed rain or seedbank densities was variable; however, combining both components improved the fit of regression describing seedling recruitment.

A study at Fairbanks, AK, was started in 1984 to determine soil seed longevity of 17 weed species. Seeds were buried in mesh bags 2 and 15 cm deep and were recovered 0.7, 1.7, 2.7, 3.7, 4.7, 6.7, 9.7, and 19.7 yr later. Viability was determined by germination and tetrazolium tests. Seed viability data were fit to an exponential model, separately for each depth, and the likelihood-ratio test was used to determine whether seed-viability decline was affected by burial depth. Depth of burial had a significant effect on viability decline of prostrate knotweed, marsh yellowcress, bluejoint reedgrass, and wild oat. By 19.7 years after burial (YAB), all seeds of common hempnettle, quackgrass, wild oat, foxtail barley, and bluejoint reedgrass were dead. Seeds of 12 other species were still viable: corn spurry (0.1%), prostrate knotweed (0.3% at 2 cm, 0.8% at 15 cm), flixweed (0.5%), pineapple-weed (0.6%), shepherd's-purse (1.3%), wild buckwheat (1.5%), common chickweed (1.6%), rough cinquefoil (1.8%), common lambsquarters (3.0%), Pennsylvania smartweed (3.3%), marsh yellowcress (8.5% at 2 cm, 0.3% at 15 cm), and American dragonhead (62.2%). Seed dormancy at 19.7 YAB was very low for all species (< 4%) except for American dragonhead, common lambsquarters, Pennsylvania smartweed, and shepherd's-purse, which had seed dormancies of 100, 27, 25, and 38%, respectively. Seed longevity was not increased by cold, subarctic temperatures.

A 50-yr study at Fairbanks, AK, was started in 1984 to determine soil seed longevity of 17 weed species. Seeds were buried in mesh bags 2- and 15-cm deep and were recovered 0.7, 1.7, 2.7, 3.7, 4.7, 6.7, 9.7, 19.7, and 24.7 yr later. Viability was determined using germination and tetrazolium tests. By 24.7 yr after burial (YAB), no viable seeds were found for common hempnettle, flixweed, foxtail barley, quackgrass, and wild oat. Bluejoint reedgrass, which had no live seed 19.7 YAB, again had viability (1% at 15 cm) 24.7 YAB. Seeds of 11 other species were still viable: American dragonhead (52%), marsh yellowcress (11 and 3.0% at 2 and 15 cm respectively), common lambsquarters (2.8%), prostrate knotweed (2.8% at 15 cm), shepherd's-purse (2.8%), pineapple-weed (2.6%), rough cinquefoil (2.3%), Pennsylvania smartweed (1.1%), common chickweed (0.4%), wild buckwheat (0.3%), and corn spurry (0.1%). Seed dormancy 24.7 YAB was very low (< 10%) for all species except American dragonhead (99%), shepherd's-purse (40%), marsh yellowcress (23% at 2 cm), Pennsylvania smartweed (18%), and rough cinquefoil (14%). At the beginning of the study, declines in seed longevity were uniform between replicates, but variability between replicates increased over time for all species except American dragonhead, suggesting that some soil microsites are more favorable for seed survival and may be seedbank “safe sites.” Results of this study demonstrate that nonrandom seed mortality contributes to the spatial heterogeneity of seed populations in the soil seedbank.