R.G. Smith, K.L. Gross
Presented at the All Scientist Meeting (2003-09-12 )
A number of recent experimental studies in grasslands have shown that plant diversity can have important effects on a number of community and ecosystem processes. We have recently established an experiment at the KBS LTER in which cropping system diversity is manipulated by varying the number of crops in a row-crop rotation and the use of cover crops. The twenty experimental treatments in the “Biodiversity Plots Experiment” were established in 2000 and span a realistic range of crop diversities including no-crop fallows (spring and fall-tilled), single species monocultures (continuous corn, soybean, and winter wheat), two-crop (corn-soybean, wheat-soybean) and three-crop rotations (corn-soybean-wheat), with and without cover crops. All treatments are managed without chemical inputs. We have been monitoring the effects of cropping system diversity on the associate weed communities by sampling the soil seed bank (early May, just after spring crops are planted) and emergent weed community (biomass harvest in late August). Interestingly, cropping system diversity (e.g. the number of crops in the rotation or use of cover crops) had little effect on weed seed densities, emergent weed biomass, species richness, or species evenness. Multivariate analysis of emergent weed community composition among treatments revealed that weed communities in fall fallows and winter wheat treatments are distinct from those in spring-sown crops and fallows. These results suggest that initial differences in weed community composition associated with cropping system diversity are driven by differences in tillage time (fall vs. spring) and that the timing of management activities is initially a more important factor than rotational diversity in determining weed community composition and structure in row-crop systems.
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