Greenhouse Gas Flux Response in Biochar‐ and Compost‐Amended Lawn Soils Under Simulated Water Saturation Conditions

ABSTRACT Understanding greenhouse gas emission dynamics in lawn soils is important for improving climate change mitigation strategies in urban and suburban landscapes. In this greenhouse mesocosm study, carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) fluxes were measured from 12 turfgrass soil columns arranged in an unreplicated, completely randomized 4 × 3 factorial design. Four amendment treatments (biochar, compost, bio‐com [1:1 volume ratio of biochar and compost], and unamended control) were combined with three water‐table conditions (full saturation, half saturation, and unsaturated), with a single column representing each treatment combination. Columns were irrigated at 1 cm day −1 for 24 days, followed by 14 days of contrasting water‐table conditions and a 25‐day drying period without irrigation. When averaged across all water‐table conditions, compost‐amended columns (compost or bio‐com) produced higher CO 2 fluxes (∼6 µmol m −2 s −1 ) than biochar‐amended and control columns (4.5–5.0 µmol m −2 s −1 ). CO 2 fluxes were positively correlated with air temperature and negatively correlated with soil moisture. Biochar‐amended columns maintained high soil moisture (∼95%) throughout the study, demonstrating its greater moisture retention than compost‐amended columns (<23%). During saturation and subsequent drainage, CH 4 fluxes peaked at 324 nmol m −2 s −1 , whereas N 2 O fluxes exhibited a transient pulse, reaching 5–8 nmol m −2 s −1 . Overall, amendment type and temperature primarily regulated CO 2 emissions, whereas water‐table conditions had a stronger influence on CH 4 emissions and the occurrence of N 2 O emission pulses.