Continuous Organic Zero-till: Elusive or Illusory.

There is considerable interest in reducing tillage among organic farmers in the Great Plains. A long-term study was established in 2009 to determine if continuous organic zero-till (OZ) systems could be developed and implemented successfully in western North Dakota. A 5-yr crop rotation that includes four grain crops (winter wheat [Triticum aestivum L. emend. Thell.], field pea [Pisum sativum subsp. sativum], navy bean [Phaseolus vulgaris L.] and proso millet [Panicum miliaceum L.]) along with winter rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) cover crops was established under conventional- or clean-till (CT), reduced-till (RT), and OZ management in a randomized complete block with each crop phase by tillage combination replicated five times. Wheat and pea grain yields in the continuous OZ system have been < 60% of those produced under CT (P < 0.05). Harvestable grain has not been produced during the navy bean and millet phases under OZ. Weed pressure has been severe and is worsening in the OZ system, in part because of the failure of fall-seeded rye and vetch cover crops to overwinter and produce adequate amounts of above-ground, rolled-crimped biomass to suppress weeds the following growing season. Use of sheep (Ovis aries) and acetic acid prior to seeding and after harvesting grain crops have failed to control perennial and several annual weed species. Lack of weed control currently prevents continuous OZ from being a viable option for most organic farmers in the Great Plains and similar climatic regions.