Impacts of Cover Crops and Crop Residues on Phosphorus Losses in Cold Climates: A Review

The use of cover crops and crop residues is a common strategy to mitigate sediment and nutrient losses from land to water. In cold climates, elevated dissolved P losses can occur associated with freeze–thaw of plant materials. Here, we review the impacts of cover crops and crop residues on dissolved P and total P loss in cold climates across ∼41 studies, exploring linkages between water‐extractable P (WEP) in plant materials and P loss in surface runoff and subsurface drainage. Water‐extractable P concentrations are influenced by plant type and freezing regimes. For example, WEP was greater in brassica cover crops than in non‐brassicas, and increased with repeated freeze–thaw cycles. However, total P losses in surface runoff and subsurface drainage from cropped fields under cold climates were much lower than plant WEP, owing to retention of 45 to >99% of released P by soil. In cold climatic regions, cover crops and crop residues generally prevented soil erosion and loss of particle‐bound P during nongrowing seasons in erodible landscapes but tended to elevate dissolved P loss in nonerodible soils. Their impact on total P loss was inconsistent across studies and complicated by soil, climate, and management factors. More research is needed to understand interactions between these factors and plant type that influence P loss, and to improve the assessment of crop contributions to P loss in field settings in cold climates. Further, tradeoffs between P loss and the control of sediment loss and N leaching by plants should be acknowledged. Core Ideas Winter crop covers reduce soil erosion but may enhance dissolved P loss under cold climates. In cold climates, freeze–thaw cycles increase dissolved P release from plants and soils. Plant water‐extractable P varies with crop species, hardiness, and freeze regimes. Phosphorus losses in runoff and leaching are complicated by soil, hydrology, and management. Assessment of crop impacts on P loss should consider tradeoffs and future climates.