Valorization of vitamin C industrial byproduct as a soil amendment: Environmental benefits and enhancement of maize productivity.

The mechanisms by which vitamin C residue after evaporation (RAE) regulates soil microbial processes and maize productivity remain unclear. A randomized complete block field trial was conducted in 2023. The trial evaluated the effects of RAE on soil nutrient availability, microbial functional potential, and maize productivity, with three treatments: (1) untreated control (CK), (2) low RAE rate (LR: 150 L/ha), and (3) high RAE rate (HR: 300 L/ha), each with four replicates. RAE was applied through drip irrigation at the six-leaf and fourteen-leaf stages of maize. RAE application increased soil dissolved organic carbon (5.75-16.73%) and mineral nitrogen availability, with ammonium and nitrate increasing by 24.79-51.04% and 23.24-69.25%, respectively, whereas soil organic carbon and total nitrogen, phosphorus, and potassium were unchanged. RAE also increased soil microbial biomass, soil respiration, and key enzymes involved in carbon, nitrogen, and phosphorus cycling, whereas HR shifted bacterial community composition and increased copy numbers of functional genes involved in these processes. RAE further enhanced maize physiological performance: photosynthetic rate increased by 12.88-33.41%, relative chlorophyll content (SPAD) by 9.73-25.10%, and dry matter translocation by 18.79-31.93%, resulting in a grain yield increase of 8.26-13.46% in 2023. Grain yield was recorded during 2023-2025, confirming the stability of this yield response. RAE application enhanced soil nutrient availability and microbial functional potential, thereby improving maize physiological performance and grain yield, likely through the regulation of nutrient cycling and microbial processes. These findings provide a value-added management strategy for utilizing RAE in agroecosystems.