Weed seed consumption experiments involving comparison of rates of seed loss by seed feeders were conducted over a five-week period in low-input (no insecticide, low herbicide usage) conventional- and no-tillage soybean agroecosystems. Seeds of four broadleaf weed species (ragweed[Ambrosia artemisiifoliaL.], pigweed[Amaranthus retroflexusL.], sicklepod[Cassia obtusifoliaL.], and jimsonweed[Datura stramoniumL.]) and one grain crop species (wheat[Triticum aestivumL.]) were provided in a free choice design at densities of 10, 25, and 50 seeds/24 cm3. Approximately 2.3 times more seeds overall, and 1.4 times more large seeds as a group were consumed in notillage systems than in conventional-tillage systems. In our experimental low-input, notillage treatments, large ground beetles (Carabidae: Coleoptera) (15–25 mm) and mice preferentially fed on the larger seed species, while small carabids (< 15 mm), ants and crickets, fed almost exclusively on the smaller seed species. Carabid beetles were responsible for more than half of all seeds consumed. Laboratory and field studies indicated that ground beetles selectively consumed specific seed species. In conventional-tillage, ants were one of the dominant consumers of seeds, suggesting different patterns of resource partitioning in each tillage system. We suggest that selective feeding by arthropod seed feeders, in combination with their high number, could affect the species composition and possibly the abundance of weeds in low-input, no-tillage agroecosystems.
/ Sampling data are provided and concepts discussed regarding soil and foliage arthropod communities in conventional and no-tillage soybean agroecosystems Soil arthropod communities from the two cropping systems were also compared with that from an adjacent old field.Biweekly arthropod samples were collected from conventional, no-tillage, and old-field systems Soil arthropods were sampled by quadrat and pitfall trap methods, foliage arthropods were collected by sweep net Ouadrat sampling revealed that ground beetle number, species diversity, and biomass were significantly higher (P < 0.05) in no-tillage than in conventional tillage systems. Pitfall trap data indicated higher densities and species diversity for most major soil macro-arthropod guilds Foliage arthropod guilds from notillage treatments showed higher species diversity throughout the growing season than those of conventional tillage, possibly because of greater structural diversity provided by weeds and litter in notillage systems No-tillage systems supported a larger and more diverse arthropod community than conventionally grown soybeans, suggesting a need for pest management strategies that simultaneously consider many variables. Both foliar grazing and leaf nitrogen content were higher in conventional than in no-tillage systems, indicating a possible causal connection between soil tillage and insect herbivory rates
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SUMMARY(1) The nitrogen dynamics of conventional and no-tillage agro-ecosystems are compared. Sorghum/rye (1978)(1979) cropping systems were followed in rotation by soybean/rye (1980)(1981) systems. Measurements of ecological processes including crop and weed production, litter decomposition, insect consumption, along with solution chemistry of soil, precipitation, throughfall, and ground water provided the data base for modelling nitrogen cycling in the two tillage systems for four complete annual farming cycles (two sorghum/rye and two soybean/rye).(2) Summary budgets indicated that both similar and dissimilar nitrogen cycling processes were occurring in conventional and no-tillage agro-ecosystems. Differences between agro-ecosystems were not definitive but suggestive of a trend of increasing ecosystem divergence through time.(3) Nitrogen fluxes between several agro-ecosystem component pairs were increased by ploughing. Crop shoot to root ratios differed between tillage treatments, suggesting distinct nitrogen uptake and storage strategies.(4) As a consequence of leaving crop and weed residues on the soil surface, no-tillage soil maintained higher (t30, P < 0.05) organic nitrogen in the upper soil layer (0-10 cm) than conventionally tilled soil.(5) Grain yields for the 4-year period were insensitive to tillage practices except during a drought year (1981) when no-tillage systems yielded higher (t30, P < 0.01) than conventional tillage.(6) Arthropod species diversity and weed biomass were higher (t30, P < 0.05) on several occasions in no-tillage systems.(7) We conclude that soil tillage practices were important regulators of nitrogen flux between agro-ecosystem components and nitrogen storage capacity within them. The undisturbed soil and litter layers of no-tillage systems generate complex decomposition subsystems which mimic those found in natural terrestrial ecosystems. We speculate that biologically-mediated nitrogen-retention mechanisms develop and operate to a greater extent in no-tillage than in conventional tillage systems.
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