Weed Seedbank and Weed Biomass Dynamics in a Long-Term Organic Vegetable Cropping Systems Experiment

Abstract

AbstractMost previous research on changes in weed abundance and community composition in cropping systems has focused on field crops. The study presented here examined changes in the weed seedbank and aboveground biomass in four organic vegetable cropping systems over a 10-yr period. The systems included an Intensive system with six crops per 4-yr rotation, an Intermediate system with one cash crop per year, a Bio-extensive system with alternating cash crop and tilled fallow years plus prevention of seed rain, and a Ridge-tillage system with one cash crop per year. Systems also differed in the types and number of cover crops between cash crops. During the course of the experiment, the weed community shifted from one dominated by summer annual broadleaf species that reproduce at the end of their lives to a community dominated by summer and winter annuals that mature rapidly. This shift in community composition can be attributed to the change in land use from conventionally managed corn (Zea maysL.) and alfalfa (Medicago sativaL.) to organic vegetable production. In particular, crop rotations with diverse preplantings and postharvest tillage dates interrupted the life cycle of common lambsquarters (Chenopodium albumL.) and pigweed species (Amaranthusspp.: mostly Powell amaranth [Amaranthus powelliiS. Watson], with small numbers of redroot pigweed [Amaranthus retroflexusL.] and smooth pigweed [Amaranthus hybridusL.]), while favoring a diverse assemblage of quickly maturing species. The study thus demonstrates that an appropriate crop rotation can control the seedbank of weeds likeC. albumthat potentially persist well in the soil. The Ridge-tillage system greatly reduced the frequency and depth of tillage relative to other systems while effectively suppressing perennial weeds. The early-reproducing annuals, however, became more abundant in the Ridge-tillage system than in the other systems, primarily due to escapes along the edge of the scraped ridges. The tilled fallow periods coupled with prevention of seed rain in the Bio-extensive system substantially reduced weed abundance through time and relative to the other systems.