Exploring how multi-year cover crop use alters above and belowground weed communities in limited tillage corn-soybean systems

Elizabeth Oys¹Fernanda Krupek²Christopher A Proctor³Katja Koehler-Cole⁴Andrea Basche^1*

• ¹University of Nebraska System, Lincoln, United States
• ²Crop and Horticultural Sciences, The Ohio State University, Columbus, Ohio, United States
• ³Department of Agronomy and Horticulture, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
• ⁴University of Nebraska Extension, University of Nebraska System, Lincoln, Nebraska, United States

Over the last several decades, intensive production of corn (Zea mays L.) and soybeans (Glycine max L.) in the United States includes widespread use of herbicide-tolerant crops, contributing to soil management with reduced tillage. The continuous use of herbicides with the same modes of action has led to accelerated presence of herbicide resistance in weed populations, particularly from the Amaranthaceae family. Integrated weed management tools such as the use of cover crops are increasingly recognized as cultural approaches with the potential to reduce herbicide-driven selection pressure. We utilized six multi-year (4-7 years) cover crop research trials in corn-based crop rotations to measure germinable weed seedbanks and aboveground weed density and biomass. This included four on-farm and two university research experiments across eastern and central Nebraska with histories of no or reduced tillage. Three sites showed increases in Amaranthaceae family (pigweed) seedbank densities under cover crops (137-355%) compared to the no cover crop check, but no differences in total weed seedbank densities were found. Cover crops reduced aboveground total weed density and biomass at two sites, however, increases from the pigweed seedbank were not expressed at any sites. Multivariate analyses revealed that the species composition of the seedbanks under cover crops was distinct from the check at two sites, suggesting cover crops may influence weed seedbank composition over time. This work underscores the value of exploring integrated weed management as well as monitoring weed populations in the soil seedbank and aboveground emerged species , particularly in cropping systems with reduced soil disturbance. We encourage more research on the multi-year use of integrated weed management approaches such as cover crops to better understand the complexity of how such approaches shift weed communities, especially with respect to problematic herbicide-resistant weeds.