Evaluating the impact of manure-derived hydrochar soil amendments on greenhouse gas fluxes: A greenhouse experiment using soil mesocosms and corn plants

Animal manure is an agricultural by-product that presents both nutrient value and environmental challenges, particularly through nutrient leaching and greenhouse gas (GHG) fluxes. Hydrothermal carbonization (HTC) offers a potential management strategy that converts wet manures into hydrochar, which is a more stable and nutrient-retentive amendment. This study evaluated how hydrochar derived from dairy manure, swine manure, and poultry litter, applied at 15 or 30 metric tons/ha, influences GHG fluxes and corn biomass production in a controlled greenhouse experiment using soil mesocosms with two fertilization histories (dairy-manure vs. inorganic/chemical-only). All treatments received an equal total nitrogen input through combinations of hydrochar-derived N and urea. Hydrochar treatments tended to reduce cumulative N 2 O fluxes, although not always significantly, compared to the urea-only control, with the largest reductions occurring after the second urea application. Across feedstocks, hydrochar treatments tended to show higher cumulative CO 2 fluxes, although not statistically significant, relative to the control, with 15 tons/ha applications producing higher CO 2 fluxes and more corn biomass compared to 30 tons/ha. Methane fluxes exhibited no consistent treatment-level trends. Corn biomass tended to be higher in the 15 tons/ha hydrochar treatments and lower in the 30 tons/ha treatments relative to the control. Overall, findings indicate that partially replacing urea fertilizer with hydrochar, can potentially increase biomass while reducing cumulative N 2 O fluxes. Generally, the increases in CO 2 fluxes from hydrochar did not fully offset the reductions in N 2 O fluxes at the system level. The results suggest that hydrochar amendments can offer an agronomically efficient and environmentally beneficial nutrient-management strategy.