Submitted to: Western Society of Weed Science Research Reports
Publication Type: Research Notes
Publication Acceptance Date: 1/6/2015
Publication Date: 3/15/2015
Citation: Anderson, R.L. 2015. Alfalfa suppression of weeds is affected by preceding crop. Western Society of Weed Science Research Reports, pp. 21-22.
Interpretive Summary: Organic producers are interested in no-till systems, but they are concerned about controlling weeds without tillage. We proposed a complex rotation that includes a 3-year interval of alfalfa to help manage weeds. This study showed that alfalfa is more suppressive of weeds when planted after soybean than after either spring wheat or corn. The benefit of complex rotations on suppressing weeds may be sufficient to enable producers to continuously no-till in organic farming. If so, producers will protect and preserve the health of their soils.
Technical Abstract: Organic producers are seeking alternative tactics for weed control so that they can reduce their need for tillage. In this study, we examined the impact of the preceding crop on alfalfa suppression of weeds. Alfalfa was most competitive with weeds following soybean. When following spring wheat, volunteers and fall weed growth killed approximately 25% of the alfalfa seedlings. When following corn, crop residues on the soil surface interfered with alfalfa seed placement at planting, and reduced alfalfa stands 10%. Weed biomass comprised less than 1% of the plant community (alfalfa + weeds) in the third forage year, but 23% of the plant community when following spring wheat. Alfalfa yield was also 15% higher following soybean compared with spring wheat as a preceding crop. We have proposed a complex rotation of 5 crops organized in a 9-year interval. Based on this research, we revised the rotation to be: corn-soybean-winter wheat-oat-corn-soybean-alfalfa (for 3 years).