Substitution of fiber hemp for corn did not affect soil greenhouse gas emissions from a Kentucky cropping system

Abstract Industrial hemp's return to American agriculture has been accompanied by claims of the crop's carbon neutrality, primarily due to its commercial applications. While carbon can be sequestered within products made with hemp fiber, there is little empirical evidence quantifying greenhouse gas contributions from the crop's production. Here we quantified fiber hemp's soil‐to‐atmosphere greenhouse gas fluxes and root production throughout the 2022 and 2023 growing seasons in central Kentucky and compared them to those of corn cultivated under similar conditions. Daily gas fluxes were measured from the plots throughout the growing season, accompanied by monthly soil sampling (0–10 cm) and root sampling (0–30 cm) at crop harvest. For both years, hemp and corn plots emitted similar cumulative amounts of carbon dioxide warming equivalents (2.1 ± 0.2 Mg ha −1 ). Nitrous oxide emissions and methane uptake were significantly greater in corn in 2022 but were similar in 2023. Soil permanganate oxidizable carbon for each crop was similar at all time points measured, though there was a seasonal trend, suggesting comparable labile soil organic matter contributions to gas emissions. End of season in‐row root measurements in 2022 and 2023 revealed that corn plots contained up to 3.5 times more root biomass than hemp at both the 0‐ to 10‐ and 10‐ to 30‐cm depth profiles. Under these cultivation conditions, fiber hemp released similar amounts of greenhouse gas equivalents while storing significantly less carbon belowground in roots than corn, calling into question the idea that hemp cultivation is likely to improve the short‐term environmental sustainability of the cropping system.