Soil carbon stocks in cultivated Luvisols respond positively to long-term agronomic practices with different degrees of perennial forage inclusion

Data that are relevant, substantive, and reliable are needed to verify long-term management effects on carbon (C) stocks in agricultural soils. The Breton Plots research facility in West Central Alberta, Canada, provides a unique opportunity to investigate how diverse long-term agricultural practices have influenced C storage in low-fertility Luvisolic soils from boreal regions. The Classical Plots experiment (est. 1930) includes unamended, conventionally fertilized, and manured sub-treatments of a wheat-fallow and 5-year rotation comprising annual grains (3 yr) and perennial forage (2 yr). The Hendrigan Plots experiment (est. 1980) includes a continuous forage system; a continuous grain system; and an 8-year agroecological rotation of annual grains (4 yr), leguminous green manure (1 yr), and perennial forage (3 yr). Soil organic carbon (SOC) stocks were reported on an equivalent soil mass basis in various intervals corresponding to a maximum depth of 90 cm. Compared to continuous grain cropping, total SOC stock was 49 % lower under fallow and, on average, 9 % higher under forage-inclusive rotations. Compared to unamended treatments, conventional fertilizer and manure increased SOC stocks by an average of 7 % and 39 %, respectively. Compared to continuous grain cropping, using the 2024 valuation of carbon ($80 t CO 2 -e −1 ) in Canada, SOC stock differences translated into a loss of approximately $11,000 CAD ha −1 under fallow, and gains exceeding $5000 CAD ha −1 under continuous forage or agroecological management. This work clarifies how Luvisolic soils can be managed to optimize SOC stocks and how C valuation could incentivize agricultural practices conducive to this goal.