Weed management is a primary concern of organic farmers. Crop rotation is an important potential management approach for regulating weed seed populations in the soil of organic farming systems. This research was conducted to determine the effect of three organic crop rotations on the weed seedbank during the first 6 yr of a long‐term cropping systems experiment at Beltsville, MD. The rotations consisted of (i) a 2‐yr corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation, (ii) a 3‐yr corn–soybean–wheat (Triticum aestivum L.) rotation, and (iii) a 4‐yr corn–soybean–wheat–red clover (Trifolium pratense L.)/orchardgrass (Dactylis glomerata L.) hay rotation. Weed seed populations were determined by a greenhouse emergence assay using soil samples taken in the early spring of each year. The seedbanks of smooth pigweed (Amaranthus hybridus L.) and common lambsquarters (Chenopodium album L.) preceding corn were usually lower following the hay years of the 4‐yr rotation or the wheat year of the 3‐yr rotation than following the soybean year of the 2‐yr rotation. However, annual grass seedbanks preceding corn tended to be higher following the hay years of the 4‐yr rotation than following the wheat year of the 3‐yr rotation or the soybean year of the 2‐yr rotation. Seedbanks in the 3‐ and 4‐yr rotations were similar to those of the 2‐yr corn–soybean rotation (higher smooth pigweed and common lambsquarters and lower annual grass) when these longer rotations began with a corn–soybean sequence than with other sequences. Sequences beginning with hay had lower smooth pigweed and common lambsquarters seedbank populations than all other sequences. The seedbank in spring significantly predicted weed abundance at maturity in corn in at least 2 of 4 yr for all species. Results show that longer rotations with more phenologically diverse crops can reduce seedbank populations and abundance of important annual broadleaf weed species in organic production systems.

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The World Trade Organization (WTO) initiated the globalization of world trade, and increasing concerns for the quality of the environment have resulted in discussions about agricultural policy involving many different perspectives. There are several issues linking trade liberalization, agriculture and the environment, one implicitly assuming that the more efficient allocation of resources and high income are associated with the improvement of agro-environmental quality. Another view is that agricultural trade policies influence crop-production patterns, farming practices and input use. The net effect is that each approach cancels out some of the influence of the other. Two examples from Mexico and Bangladesh point out that agro-environmental responses to free trade are non-linear and that it is not easy to draw a simple causal relationship between free trade and the agroenvironment. A basic challenge before the research community is to confront reductionist approaches, as traditional research into trade–agriculture–environment interactions reveals difficulty in dealing with the knowledge gaps. A transdisciplinary, systems approach provides one possibility for dealing with the needs of free trade in agriculture.