Impacts of cover crop planting dates on soils after four years

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AbstractImpacts of cover crop (CC) mixes and early CC planting on soil properties, CC biomass production, and CC biomass C input are not well understood. We assessed CC planting date (pre‐ or post‐harvest) and CC type (rye [Secale cereale L.], mix of winter pea [Pisum sativum L.], hairy vetch [Vicia villosa L.], rye, and radish [Raphanus sativus L.], or no CC) effects on soil physical properties, organic matter, and CC biomass C input under three no‐till continuous corn (Zea mays L.) and corn‐soybean (Glycine max L.) sites in the eastern Great Plains after 4 yr. Across sites and years, pre‐harvest‐planted CCs produced 0.81 ± 0.52 (mean ± SD), post‐harvest‐planted 0.59 ± 0.44, rye 0.83 ± 0.52, and mix 0.57 ± 0.42 Mg biomass ha−1. Compared to no CC, pre‐ and post‐harvest–planted CC effects varied by site. Pre‐harvest–planted CCs increased wet‐aggregate stability by 17% and particulate organic matter by 31% under continuous corn at one of three sites compared with post‐harvest‐planted CCs. Similarly, the CC mix had variable effects on cone index but reduced bulk density by 7% at one site under continuous corn and increased wet‐aggregate stability by 21% at another site under corn−soybean. Planting date, but not CC type, effects were slightly more evident under continuous corn than corn−soybean. Across sites and years, pre‐harvest‐plant CC had 0.29 ± 0.38 Mg biomass C ha−1, post‐harvest‐planted 0.22 ± 0.30, rye 0.33 ± 0.37, and the mix 0.16 ± 0.27. Low CC biomass (<1 Mg ha−1) production may explain the limited CC effects. Overall, pre‐harvest‐planted CCs and CC mixes had minimal effects on soil properties in this region after 4 yr.