Cover crop impact on weed dynamics in an organic dry bean system

Authors: HILL, ERIN - Michigan State University; RENNER, KAREN - Michigan State University; SPRAGUE, CHRISTY - Michigan State University; Davis, Adam

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2015
Publication Date: 4/24/2016
Citation: Hill, E., Renner, K., Sprague, C., Davis, A.S. 2016. Cover crop impact on weed dynamics in an organic dry bean system. Weed Science. 64:261-275.

Interpretive Summary: Growing cover crops in between grain crops can help boost soil fertility, but can also have both positive and negative effects weed management. A better understanding of how different cover crop species influence weeds will help farmers to design better integrated cropping systems. Our research assessed the influence of cover crops on weed growth and population dynamics in organic dry beans. Medium red clover, oilseed radish, and cereal rye were planted in the spring or late-summer prior to dry beans; a no cover crop control was also included. Oilseed radish and cereal rye did not affect the number or size of weeds. When large amounts (> 5 Mg/ha) of red clover biomass were incorporated into the soil, weed density and biomass in dry beans were sometimes greater than the no cover control and soil inorganic nitrogen was often higher. Further analysis revealed that cover crop C:N ratios and N content influenced soil N at the time of dry bean planting, which then strimulated weed biomass at V2. Organic cropping system design needs to take into account potential increases in weed growth when N-rich cover crops are grown.

Technical Abstract: Cover crops have the potential to enhance crop rotations by increasing diversity and enriching agroecosystems. Weed suppression, nutrient provisoning, and enhancements to soil biota and structure are benefits of cover crops in cropping systems, including organic dry bean production. The late spring planting date (early- to mid-June in Michigan) of dry beans, compared with other warm season field crops, allows more time for spring growth of cover crops prior to bean planting. Our research assessed the influence of cover crops on: 1) weed dynamics in organic dry beans and 2) weed seed persistence over time following cover crop incorporation. Medium red clover, oilseed radish, and cereal rye were planted in the spring or late-summer prior to dry beans; a no cover crop control was also included. Following cover crop incorporation, weed emergence and biomass were monitored during the dry bean growing season. Eleven or more site-years of field data were collected for each cover crop treatment between 2011 and 2013, allowing for the exploration of how cover crops influence weed communities through structural equation modeling (SEM), in addition to traditional analyses. To assess weed seed persistence, common lambsquarters, giant foxtail, and velvetleaf seeds were buried in the red clover, cereal rye, and no cover control treatments and then retrieved 0, 1, 2, 4, 6, and 12 months after incorporation. Oilseed radish and cereal rye did not directly impact weed density or biomass when measured during the dry bean season. Cereal rye residue increased giant foxtail and velvetleaf seed persistence compared with the no cover crop control in one of two years. When red clover biomass exceeded 5 Mg/ha, weed density and biomass in dry beans were sometimes greater than the no cover control and soil inorganic nitrogen was often higher. Red clover residues decreased the persistence of common lambsquarters seed in one of two years. SEM revealed that cover crop C:N ratios and N content influenced soil N at the time of dry bean planting, which then influenced weed biomass at V2. Cover crops’ influence on weed seed banks, weed emergence, and soil inorganic N are important considerations in organic cropping systems.