Do cover crop mixtures improve soil physical health more than monocultures?

Rationale and PurposeAdding multispecies cover crop (CC) mixtures could diversify the current simplified crop rotations and enhance soil health more than monoculture CCs. Further, CC mixtures with diverse plant species could adapt better to changing climatic and environmental conditions than monoculture CCs. However, our current understanding of the soil benefits of CC mixtures is still limited. This review discussed whether CC mixtures are better than monoculture CCs to improve soil physical health.MethodsAll studies published up to May 25, 2023 comparing soil physical properties between CC mixtures and their constituents grown as monocultures were searched in the available databases. To avoid potential sampling bias, only studies that compared mixtures against all its constituents grown alone were discussed.ResultsCover crop mixture studies on soil physical properties were relatively few. Mixtures did not reduce soil bulk density in 83% of cases, penetration resistance in 75%, wet aggregate stability in 67%, and dry aggregate stability and saturated hydraulic conductivity in 100% compared with monoculture CCs. Mixtures had inconsistent effects on water infiltration and plant available water. The number of CC species in the mixture and management duration do not differently affect mixture impacts. The limited or no differences in soil physical properties between mixtures and monocultures could be due to the similarities in CC biomass production and soil C between these two systems.ConclusionCover crop mixtures do not enhance soil physical properties relative to monoculture CCs in most cases. However, the few cases where mixtures outperformed monocultures suggest soil benefits of mixtures should be evaluated on a site-specific basis. More long-term (> 10 yr) data are needed for more definitive conclusions.