Cover crops and weed suppression in the U.S. Midwest: A meta‐analysis and modeling study

Abstract

In addition to soil health and conservation benefits, cover crops (CCs) may offer weed control in the midwestern United States, but individual studies report varying effects. We conducted a meta-analysis of studies measuring weed biomass (WBIO) or density (WDEN) in paired CC and no-cover treatments in corn (Zea mays L.)-soybean [Glycine max (L.) Merr] rotations in the U.S. Midwest. Fifteen studies provided 123 paired comparisons of WBIO and 119 of WDEN. Only grass CCs significantly reduced WBIO, while no CC reduced WDEN. We found no evidence CC management factors (e.g., termination method) directly affected outcomes. Our dataset showed that a 75% reduction in WBIO requires at least 5 Mg ha −1 of CC. Simulations from a process-based model (SALUS) indicated achieving 5 Mg ha −1 requires substantially earlier fall planting and later spring termination in most years, conflicting with typical cash-crop planting and harvesting. We conclude CCs significantly reduce WBIO, but current CC management constraints render these reductions variable and uncertain.

Complete Issue

“…Studies in summer annual weed biomass. These studies suggest that about 2.5 tons/ac of biomass is required to reduce weed biomass by 75% (Nichols et al, 2020). Several factors such as regional and environmental conditions, cropping system management, and weed species all may influence the effectiveness of cover crops on weed control, but it is clear that as cover crop biomass increases, weed biomass is decreased (McCall, 2018;Werle et al, 2017).…”

“…Several factors such as regional and environmental conditions, cropping system management, and weed species all may influence the effectiveness of cover crops on weed control, but it is clear that as cover crop biomass increases, weed biomass is decreased (McCall, 2018;Werle et al, 2017). It can be difficult to achieve the levels of cover crop biomass needed for effective weed suppression (Nichols et al, 2020); however, even at lower levels of biomass, cover crops are effective at reducing weed density (McCall, 2018;Werle et al, 2017).…”

“…In some instances, cover crops will result in reduced weed biomass or density and increase crop yield, but more often, weed decreases from increased cover crop biomass also reduce crop yields (Nichols et al, 2020). Producing adequate cover crop biomass for weed suppression generally requires tradeoffs between the cropping system and cover crop biomass.…”

Effects of Long-Term Cover Cropping on Weed Seedbanks

“…Previous research indicates a cover crop's potential for in-season weed suppression is strongly related to the cover crop's biomass production (Baraibar et al, 2018;MacLaren et al, 2019;Nichols et al, 2020a;Smith et al, 2020). Cover crops might reduce weed seedbank densities via several mechanisms, all of which could conceivably be intensified with increases in the quantity of cover crop biomass produced.…”

“…There is evidence cover crops can reduce weed biomass in many production contexts (Baraibar et al, 2018;MacLaren et al, 2019;Smith et al, 2020), and specifically in midwestern maizesoybean systems (Nichols et al, 2020a). In other production systems, there is also evidence cover crops can reduce weed seed densities in the soil (Moonen and Bàrberi, 2004;Mirsky et al, 2010;Alonso-Ayuso et al, 2018) and decrease the survival success of herbicide-resistant weeds (Cholette et al, 2018;Wallace et al, 2019).…”