Organic dry bean (Phaseolus vulgaris L.) response to crop rotation, row spacing, and weed management in Minnesota

Abstract

In the Upper Midwest, edible grain legumes like dry beans (Phaseolus vulgaris L.) provide an opportunity for year-round access to sustainably grown, nutritious local foods. While the demand for organic local foods is increasing, only 0.3% of total dry bean acreage in MN is organic. Research is needed to identify dry bean market classes, weed management tactics, and crop rotations suitable for organic production in this region. Our overall project objective was to develop agronomic strategies to promote efficient production and high yields of dry beans, while sustaining economic viability and soil quality. A three-year rotation experiment: Phase 1) corn or alfalfa, Phase 2) six different market classes of beans, Phase 3) wheat, was conducted from 2010 to 2015 at four locations in southern Minnesota. Yield, weed competition, and soil nitrate contributions were studied pertaining to the effects of the previous crops being either corn or alfalfa in Phase 1 and beans in Phase 2. Bean yield averaged across bean types were highest following alfalfa at three of four locations. Soybean yielded the highest (2312 kg ha-1), followed by pinto (2213 kg ha-1), black (1950 kg ha-1), navy (1818 kg ha-1), heirloom (1720 kg ha-1), and kidney (1398 kg ha-1). Wheat yield was similar following all bean types. Phase 1 crop (corn or alfalfa) did not impact wheat yield despite differences in soil nitrate levels prior to production. Total weed biomass varied substantially by location. Economic analyses showed promising net returns for all dry bean classes, at least 150% higher than soybean. To evaluate alternative tillage practices and row spacing effects on dry bean and soybean yield as well as weed control, another experiment was carried out from 2012 to 2014 at two certified locations in southwestern Minnesota. The objective was to determine the combined effects of tine weeding in 38 cm rows, tine weeding and cultivation in 76 cm rows, or cultivation in 76 cm rows on black, kidney, and soybean yield and weed biomass. Across years, excessive early season moisture led to high weed populations and reduced bean yield. Both dry bean and soybean yields were 25% less in the narrow row treatments. Correspondingly, weed biomass was higher in the narrow tine weeded treatments as compared to the two wide row cultivated treatments. Total weed biomass differed among classes, with the lowest in soybean treatments (2,360 kg ha-1). While narrow rows have lead to dry bean and soybean yield increases in some conventional studies, our results demonstrate that wider rows that facilitate tillage operations may lead to better weed control and subsequently higher yields in organic systems.