Rolled winter rye and hairy vetch cover crops lower weed density but reduce vegetable yields in no-tillage organic production.

University of Minnesota M.S. thesis. May 2010. Major: Applied Plant Science. Advisors: Drs. Craig Sheaffer and Donald Wyse. 1 computer file (PDF); vi, 78 pages, appendix A.Winter annual cover crops, winter rye (Secale cereale) and hairy vetch (Vicia villosa roth.), can reduce weed density and build soil health in organic production systems. There is considerable interest in integrating cover crops and reduced tillage with organic vegetable production; but few studies have been conducted in regions with short growing seasons and cool soils such as the upper Midwest. We evaluated no-tillage production of tomato, zucchini, cauliflower, and bell pepper planted into winter rye, hairy vetch, and a winter rye-hairy vetch mixture that were mechanically suppressed with a roller-crimper at two locations in Minnesota. Average marketable yields of tomato, zucchini, and bell pepper in the cover crops were reduced 58-87%, 27-75% and 62-92%, respectively, compared to a no-cover control. Winter rye and the mixture reduced average annual weed density at St. Paul by 96% for 8-10 weeks after rolling (WAR) and hairy vetch mulch had 80% control for 2-8 WAR; while at Lamberton, there was no consistent effect of cover treatments on weed populations. Winter rye and the mixture had higher average residue biomass (5.3 and 5.7 Mgha-1) than hairy vetch (3.0 Mgha-1) throughout the season in addition to higher biomass N content in most cases. Cover crop mulches reduced soil temperature by 2.9° to 5.7° C compared to a no-cover control for 4-5 weeks after planting which delayed vegetable growth and could have contributed to reduced yields in the cover crop mulches. In addition, low levels of soil N (