Menalled, F., K. L. Gross, and M. Hammond. 2001. Weed aboveground and seedbank community responses to agricultural management systems. Ecological Applications 11:1586-1601.
The development of integrated weed management programs requires a clear understanding of the factors and mechanisms conditioning weed community dynamics in agroecosystems. This study evaluated the effect of different agricultural management Systems on the aboveground and seedbank weed communities in annual row crops at the Long Term Ecological Research project in agricultural ecology at the W. K. Kellogg Biological Station, Michigan, USA. Weed biomass and species composition were sampled for six years over two corn-soybean-wheat sequence cycles in four agricultural management systems: (1) conventional (high external chemical input, moldboard plowed); (2) no-till (high external chemical input, no tillage); (3) low-input (low external chemical input, moldboard plowed), and (4) organic (no external chemical input, moldboard plowed), A greenhouse germination study assessed variation in the abundance and composition of the weed seedbank across the studied systems in the first and sixth year of this study. Aboveground weed biomass, species density, and diversity were lowest in the conventional system, intermediate in the no-till system, and highest in the low-input and organic systems, but there were significant year-by-system interactions. Monocot and dicot species were equally common in the conventional system, whereas annual grasses, such as Digitaria sanguinalis (large crabgrass) and Panicum dichotomiflorum (fall panicum), dominated the no-till system. Two perennial weed species (Trifolium pratense [red clover] and Elytrigia repens [quackgrass]) and one annual dicot (Chenopodium album [common lambsquarters]) dominated the low-input and organic systems. A multivariate ordination of all four systems revealed close associations between the conventional and no-till systems and between the low-input and organic systems. Separate ordinations of the four management systems revealed a crop effect in the low-input and organic systems, but no differentiation in the conventional and no-till ones. The seedbank study revealed a significant increase in the number of weed seeds and species, mainly of annual grasses such as D. sanguinalis and P. dichotomiflorum, in the conventional and no-till systems over the six years of study. During the same period, the number of weed seeds declined in low-input and organic systems. Three annual dicots (Stellaria media [common chickweed], Veronica peregrina [purslane speedwell], and C. album) dominated the seedbank of the low-input and organic systems. Weed aboveground and seedbank community composition were more constant over time in the low-input and organic systems than in the conventional and no-till systems over the study period. These results demonstrate that agricultural management systems can have both immediate and long-term effects on weed species density, abundance, and diversity. The differences observed among management systems in weed biomass, species composition, diversity, and community constancy indicate challenges that exist for the development of ecologically based weed management systems in row crop agriculture.
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