| Efficient weed management in agroecosystems requires knowledge of the effects of the management system in use on weed population and community dynamics and individual weed species. Despite the recent increase in the use of no-till management systems, limited attention had been devoted to the effects of crop residues left on the soil surface after harvest on weed populations and communities. Weed seedling emergence from a known seed bank was examined in response to varying types of crop residues (corn, soybean, wheat) in combination with different amounts of residues, representing variations found in field situations. Greenhouse and no-till field experiments were performed using three seed cohorts of five annual broadleaved weeds and two annual grasses. In the field studies, species richness, which included the natural and a standard seed bank, was also assessed. Treatment effects were species-specific and often differed from year to year. Generally, increasing the amount of crop residue decreased seedling emergence and species richness. However, in some cases, crop residues stimulated seedling emergence. In the greenhouse experiment, corn and soybean residues had a greater ability to suppress weed emergence than wheat residues. In contrast, in the field experiments, wheat residues suppressed the emergence of more species than corn and soybean residues. Weed suppression appeared to be related to high residue biomass and the limited availability of suitable gaps for seedling recruitment. An increase in weed emergence was attributed to nitrogen released by decomposing residues or fertilizer application and increased moisture under residues. These findings emphasize the importance of understanding the biology and ecology of weeds with respect to their interaction with crop residues in no-till fields.;Keywords. Crop residues, no-till agriculture, weed populations, residue management, residue decomposition, weed emergence, weed management, Amaranthus retroflexus, redroot pigweed, Ambrosia artemisiifolia , common ragweed, Abutilon theophrasti, velvetleaf, Chenopodium album, lamb's-quarters, Echinochloa crusgalli , barnyard grass, Polygonum persicaria, lady's thumb, Setaria pumila, yellow foxtail. |
