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

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 N₂ 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.