Biochar and Fertilizer Type Effects on Soil Health Indicators in a Sandy Loam Ultisol of the Georgia Coastal Plain: A Two-Year Field Study

Biochar and poultry litter have been proposed as soil amendments to improve soil health in coarse-textured agricultural soils, yet their field performance under southeastern U.S. conditions remains inconclusive. This two-year field study evaluated five biochar application rates (0–44.8 Mg ha−1) combined with inorganic fertilizer or poultry litter on selected soil health indicators in a sandy loam Ultisol under sweet corn production in the Georgia Coastal Plain. Treatments were arranged in a randomized complete block design with four replications and analyzed using linear mixed-effects models. Biochar application did not significantly affect aggregate stability, pH, cation exchange capacity, soluble salts, organic matter, active carbon, or estimated nitrogen mineralization, with only a marginal three-way interaction observed for microbial respiration. Poultry litter significantly increased microbial respiration relative to inorganic fertilizer, whereas responses for the remaining soil health indicators were broadly similar between fertilizer sources. Year was the dominant source of variation, with extreme rainfall in 2024 reducing aggregate stability, soluble salts, microbial respiration, and nitrogen mineralization while increasing organic matter and active carbon. These findings indicate that short-term soil health responses were driven primarily by environmental conditions rather than management practices. Under the conditions of this study, either fertilizer source can be used successfully, whereas longer-term studies are needed to determine whether biochar aging enhances soil function in sandy loam Ultisols.