Truncating leguminous fixation and post‐harvest scavenging: Two pathways for reducing nitrate leaching in potato rotations

Abstract Nitrate leaching from intensive potato production is a significant contributor to groundwater contamination and estuarine eutrophication in Atlantic Canada. This 5‐year study (2018–2023) evaluated two cover‐cropping strategies in a barley ( Hordeum vulgare L.)–red clover ( Trifolium pratense L.)–potato ( Solanum tuberosum L.) rotation in Prince Edward Island: (1) mid‐season red clover termination followed by buckwheat ( Fagopyrum esculentum Moench) seeding, and (2) winter rye ( Secale cereale L.) established after potato harvest. Nitrate leaching was quantified using tile‐drain concentrations integrated with LEACHN‐modeled drainage. Introducing buckwheat reduced post‐potato nitrate leaching by 30.6% ( p = 0.05) in 2019/20. The early termination of red clover truncated the biological N 2 fixation period, fundamentally reducing the N pool available for mineralization and subsequent leaching. Conversely, winter rye acted through a traditional “Scavenging” pathway, reducing post‐harvest leaching by a pooled 37% ( p = 0.02) through active N uptake (average 28 kg N ha −1 ). Neither strategy significantly impacted subsequent marketable potato yields. These results demonstrate that while winter rye is a robust scavenger of residual N, the early termination of leguminous forages to plant cover crops like buckwheat provides an effective “source‐control” intervention. Overall, both buckwheat and winter rye cover cropping strategies effectively mitigated nitrate leaching in this potato‐based rotation—through different mechanisms—and offered a practical framework for reducing the environmental footprint of potato production in humid, temperate regions.