Short- and full- season soybean in stale seedbeds versus rolled- crimped winter rye mulch

Stale seedbeds are used by organic growers to reduce weed populations prior to crop planting. Rye mulches, derived from mechanically killed (rolled and crimped) winter rye cover crops, can serve the same purpose for spring-planted organic crops. Both methods can also be employed by conventional growers who face looming problems with herbicide resistant weeds. The objective of this research was to compare these methods over 2 years in central Minnesota in terms of weed seedling emergence, populations, biomass and manual-weeding times, as well as stands and yields of short-season and full-season soybean varieties planted late, in mid June. Rye mulch greatly lowered both pre- and post-planting weed populations of common annual weeds, which substantially affected necessity for augmented weed control. For instance, the need for within-crop manual-weeding was low for soybean planted into rye mulch (0-6hha(-1)), but ranged from 15 to 66hha(-1) of labor for soybean planted in stale seedbeds and augmented by inter-row cultivation. However, rye mulch lowered soybean yield potential by 800-1000kgha(-1) compared with stale seedbeds in 1 of 2 years. With organic feed-grade soybean seed valued at $1kg(-1), conventional soybean seed at $0.5kg(-1), and labor for manual-weeding at $10h(-1), the use of rye mulch compared with stale seedbeds augmented by manual-weeding are equally rational choices for organic growers in central Minnesota (assuming labor is available for hand-weeding), but rye mulches probably would be a wise financial option for conventional growers compared with hand-weeding. Lastly, full-season soybean had higher yields than short-season soybean and probably represents a prudent selection in central Minnesota, regardless of the late planting date requirements for both the rye mulch and stale seedbed systems.