We characterized the size and species composition of the weed seedbank after 35 yr of continuous crop rotation and tillage system treatments at two locations in Ohio. Spring seedbanks were monitored during 1997, 1998, and 1999 in continuous corn (CCC), corn–soybean (CS), and corn–oats–hay (COH) rotations in moldboard plow (MP), chisel plow (CP), and no-tillage (NT) plots where the same herbicide was used for a given crop each growing season. There were 47 species at Wooster and 45 species at Hoytville, with 37 species occurring at both locations in all 3 yr. Crop rotation was a more important determinant of seed density than was tillage system. Seed density was highest in NT and generally declined as tillage intensity increased. Seeds accumulated near the surface (0 to 5 cm) in NT but were uniformly distributed with depth in other tillage systems. At both locations there was a significant interaction between tillage and rotation for estimates of the total seed density. Seed density was highest in NT-CCC, with 26,850 seeds m−2 at Wooster and 8,680 seeds m−2 at Hoytville. At Wooster total seed density in CCC plots was 45 and 60% lower than in COH plots for CP and MP. In NT the total seed density was 40% greater in CCC than in COH. At Hoytville total seed density in CCC plots was 72% lower than in COH plots that were CP or MP, whereas seed density was 45% higher in CCC than in COH plots that were in an NT system. There were more significant differences in seedbank density for any given species for crop rotation than for tillage treatments. Seed densities of three broadleaves (shepherd's-purse, Pennsylvania smartweed, and corn speedwell) at Wooster and four broadleaves (yellow woodsorrel, redroot pigweed, Pennsylvania smartweed, and spotted spurge) at Hoytville were more abundant in COH (140 to 630 seeds m−2) than in CS (10 to 270 seeds m−2) or CCC (< 1 to 60 seeds m−2), regardless of the tillage system. At both locations Pennsylvania smartweed seeds were more abundant in COH (260 and 630 seeds m−2) than in other rotations (10 to 20 seeds m−2). Relative importance (RI) values, based on relative density and relative frequency of each species, were lower in CS than in CCC for common lambsquarters and five other weeds at Wooster; RI of giant foxtail was 80% lower in COH than in CCC at Hoytville. The data show how species composition and abundance change in response to crop and soil management. The results can help to determine how complex plant communities are “assembled” from a pool of species by specific constraints or filters.

Soils from long-term tillage plots at three locations in Ohio were sampled to determine composition and size of weed seed banks following 25 yr of continuous no-tillage, minimum-tillage, or conventional-tillage corn production. The same herbicide was applied across tillage treatments within each year and an untreated permanent grass sod was sampled for comparison. Seed numbers to a 15-cm depth were highest in the no-tillage treatment in the Crosby silt loam (77 800 m–2) and Wooster silt loam (8400 m–2) soils and in the grass sod (7400 m–2) in a Hoytville silty clay loam soil. Lowest seed numbers were found in conventional-tillage plots in the Wooster soil (400 m–2) and in minimum-tillage plots in the Crosby (2200 m–2) and Hoytville (400 m–2) soils. Concentration of seeds decreased with depth but the effect of tillage on seed depth was not consistent among soil types. Number of weed species was highest in permanent grass sod (10 to 18) and decreased as soil disturbance increased; weed populations were lowest in conventional tillage in the Hoytville soil. Common lambsquarters, pigweeds, and fall panicum were the most commonly found seeds in all soils. Diversity indices indicated that increased soil disturbance resulted in a decrease in species diversity. Weed populations the summer following soil sampling included common lambsquarters, pigweeds, fall panicum, and several species not detected in the seed bank.

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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-2among 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.

Studies were conducted from 1989 to 1993 in continuous no-tillage and moldboard plow corn fields to describe rates of velvetleaf seed predation with time and with seed density, and to identify principal seed predators. Rates of seed loss from the soil surface averaged 1 to 57% day−1and were equivalent in the two tillage systems. Predator populations were the same in no-tillage and moldboard plow fields. The predation rate was generally low in winter months, increased in mid-summer, and declined in late summer. In 2 of the 4 yr, predation increased in October and November. The predation rate was described by an exponential decay function of seed density, with high rates of seed loss at low densities and leveling off to a nearly constant level at densities above 600 seeds m−2. Predation was highest where seed access was not restricted, and exclosures of 6.5 and 1.6 cm2reduced predation up to 15 and 52%, respectively. Mice were important predators in the field. In laboratory feeding studies, the carabid beetleAmara cupreolata, the slugsArion subfuscusandDeroceras reticulatum, and cutworms (Agrotis ipsilon) consumed imbibed velvetleaf seeds.Amara cupreolataand A.subfuscuswere the only predators to damage unimbibed velvetleaf seeds.