Addressing the demand for agricultural waste utilization, in this study, a soil incubation-pot experiment system was employed using lettuce (Lactuca sativa) as the model crop cultivated for 61 days, the regulatory effects of four types of artificial humic acid (HACS, HACL, HAPS, HAMC) derived from corn straw, camphor tree leaves, peanut shells, and microalgae on soil physicochemical properties and crop physiological indicators were comparatively analyzed in order to elucidate the feedstock-specific mechanisms underlying differential improvements in soil amendment and crop growth. The results showed that: 1) Artificial humic acids had a moderate effect on soil pH adjustment, effectively improved soil physicochemical properties and enhanced soil fertility. Specifically, HACS applied at 64 mL/kg significantly increased soil dissolved organic carbon by 74.37% compared to CK and 23.97% compared to the treatment of direct corn straw direct-return (CS). 2) Artificial humic acids all significantly increased lettuce biomass accumulation and promoted shoot/root elongation. Among them, HACL showed superior growth promotion efficacy, while HAMC significantly improved photosynthesis, transpiration, and vitamin C content in lettuce, resulting in a net photosynthetic rate of 1.75 μmol/(m²·s), a transpiration rate of 0.66 mmol/(m²·s), and a vitamin C concentration of 353.12 mg/kg in lettuce leaves per unit fresh weight. In conclusion, soil enhancement and plant growth-promoting effects of artificial humic acids depend on the feedstock types, corn-straw-derived humic acid serves as an effective soil amendment, while microalgae-derived humic acid represents an excellent growth-promoting option for crops due to its photosynthetic regulation function. This study provides a targeted selection strategy for the agricultural functional development of artificial humic acids.