A gronomy J our n al • Volume 10 0 , I s sue 2 • 2 0 0 8 ABSTRACT During the last half-century, agriculture in the upper U.S. Midwest has changed from limited-input, integrated grain-livestock systems to primarily high-input specialized livestock or grain systems. Th is trend has spawned a debate regarding which cropping systems are more sustainable and led to the question: can diverse, low-input cropping systems (organic systems) be as productive as conventional systems? To answer this question, we compared six cropping systems ranging from diverse, organic systems to less diverse conventional systems conducted at two sites in southern Wisconsin. Th e results of 13 yr at one location and 8 yr at the other showed that: (i) organic forage crops can yield both as much dry matter as their conventional counterparts and with quality suffi cient to produce as much milk; and (ii) organic corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and winter wheat (Triticum aestivum L.) can produce 90% as well as their conventionally managed counterparts. Th e average yields for corn and soybean, however, masked a dichotomy in productivity. Combining Wisconsin Integrated Cropping Systems Trial (WICST) data with other published reports revealed that in 34% of the site-years, weed control was such a problem, mostly due to wet spring weather reducing the eff ectiveness of mechanical weed control techniques, that the relative yields of low-input corn and soybean were only 74% of conventional systems. However, in the other 66% of the cases, where mechanical weed control was eff ective, the relative yield of the low-input crops was 99% of conventional systems. Our fi ndings indicate that diverse, low-input cropping systems can be as productive per unit of land as conventional systems.

If legume cover crops are to be an effective, environmentally sound N source for corn (Zea mays L.), there must be a synchrony between legume N release and corn demand. A field study was conducted in Wisconsin during 1991 and 1992 that measured the release of legume N throughout the growing season using mesh bags, and compared resultant levels of soil mineral N following legume incorporation to those following fertilizer N applied at the recommended rate (179 kg N ha−1) and a control (no cover crop, no fertilizer) in a conventional tillage (CT) system. Corn N uptake during the growing season was also measured to determine if legume N could meet uptake demands. Hairy vetch (Vicia villosa Roth) and red clover (Trifolium pratense L.) residues decomposed rapidly, releasing half of their N within 4 wk after burial, while very little N was released after 10 wk (corresponding to corn silking). Soil tests indicated an increase in mineral N levels corresponding to legume N release, similar to those following an application of 179 kg ha−1 fertilizer N, occurring before the period of rapid N uptake by corn. Mean corn grain yields of 11.25 Mg ha−1 in 1991 and 10.89 Mg ha−1 in 1992 following the legumes were similar to those produced with 179 kg ha−1 fertilizer N, indicating that, in addition to releasing N in synchrony with the uptake pattern of corn, legumes released N in adequate amounts for corn production. Finally, postharvest levels of potentially leachable soil NO3‐N following the legumes were similar to or less than when following fertilizer. Therefore, legume cover crops can be an effective N source for corn in the Upper Midwest.

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A major challenge that organic grain crop growers face is weed management. Th e use of a rye (Secale cereale L.) cover crop to facilitate no-tillage (NT) organic soybean [Glycine max (L.) Merr.] production may improve weed suppression and increase profitability. We conducted research in 2008 and 2009 to determine the eff ect of rye management (tilling, crimping, and mowing), soybean planting date (mid-May or early June), and soybean row width (76 or 19 cm), on soybean establishment, soil moisture, weed suppression, soybean yield, and profi tability. Soybean establishment did not diff er between tilled and NT treatments; and soil moisture measurements showed minimal risk of a drier soil profi le in NT rye treatments. Rye mulch treatments eff ectively suppressed weeds, with 75% less weed biomass than in the tilled treatment by mid-July. However, by this time, NT soybean competed with rye regrowth, were defi cient in Cu, and accumulated 22% as much dry matter (DM) and 28% as much N compared to the tilled treatment. Soybean row width and planting date within NT treatments impacted soybean productivity but not profi tability, with few diff erences between mowed and crimped rye. Soybean yield was 24% less in the NT treatments than the tilled treatment, and profi tability per hectare was 27% less. However, with fewer labor inputs, profi tability per hour in NT rye treatments was 25% greater than in tilled soybean; in addition, predicted soil erosion was nearly 90% less. Although soybean yields were less in NT rye mulch systems, they represent economically viable alternatives for organic producers in the Upper Midwest.

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