Willow woodchip incorporation moderates soil carbon and nitrogen losses in a potato production system in Atlantic Canada

Abstract Maintaining soil organic carbon (SOC) in intensively managed potato systems is challenging due to frequent tillage and low residue return. A field experiment was conducted from 2019 to 2024 at the Agriculture and Agri-Food Canada Fredericton Research and Development Centre, New Brunswick, Canada, to evaluate the effects of willow (Salix spp.) woodchip incorporation on SOC, soil organic nitrogen (SON), and chemical soil properties. Willow chips harvested from a local plantation, chips were incorporated using heavy-duty offset disk to a depth of 6 inches (15.24 cm) at a rate of 40 Mg ha⁻¹ (fresh weight) in fall 2019. The willow woodchips had an average water content of 21.5% (dry matter 78.5%) and contained 47.28% C and 0.29% N (C: N 165.84), consisted primarily of woody material with bark present and no leaves, and had an approximate particle size of 20–60 mm in length, 10–30 mm in width, and 2–5 mm in thickness. Amendment input was estimated at 14.85 Mg C ha⁻¹. Surface soils (0–15 cm) were sampled annually and analyzed for SOC, SON, pH, and nutrients. SOC and SON stocks declined over time in both treatments, but losses were consistently smaller under woodchip incorporation. By 2023, SOC in amended plots was approximately 0.06 kg C m⁻² higher than in the control. SON declines were also slightly slower in the amended plots, while soil pH and most nutrient levels were unaffected. These findings suggest that woodchip incorporation may modestly reduce the rate of SOC and SON decline in potato-based systems, but the effect appears limited in magnitude and duration.