Cover crops and weed suppression in the US Midwest: A meta-analysis and modeling study.

Virginia Nichols,Bruno Basso,David Weisberger,Sarah Carlson,Andrea Basche,Rafael Martinez-Feria

doi:10.31220/osf.io/43b9n

Abstract

Abstract In addition to soil health and conservation benefits, cover crops (CCs) may offer weed control in the Midwestern United States (Midwest), 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 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 impacted outcomes. Our dataset showed 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.

Highlights

Winter annual cover crops (CCs) have been heavily promoted in the Midwestern ‘Corn Belt’region of the United States (Midwest) due to an increasing need for practices that enhance soil health and water quality
The studies include a range of site characteristics and management representative of Midwestern corn-soybean production systems (S1)
CCs significantly reduced weed biomass (WBIO) (p=0.02), which was robust against publication bias (>3000 unpublished null-studies needed; Rosenthal, 1979) and the removal of individual studies

Summary

Introduction

Region of the United States (Midwest) due to an increasing need for practices that enhance soil health and water quality. Despite clear environmental benefits (Daryanto et al, 2018; Kaspar and Singer, 2011), less than 10% of Midwestern cropland is currently managed with CCs (Seifert et al, 2018). The lack of short-term economic returns from growing CCs overwhelms long-term environmental benefits, creating a major barrier to wide adoption If CCs can reduce weed management costs, this could provide immediate monetary incentives for adoption. Previous literature syntheses have found CCs reduce weed pressure across various cropping systems, but the direction and magnitude of effects are contextspecific (Osipitan et al, 2018). Given its ubiquity and significance in the Midwest, the corn (Zea mays L.)-soybean (Glycine max (L.) Merr) production system merits explicit examination

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