BackgroundSodic saline-alkali soils restrict agricultural productivity by limiting nutrient availability and disrupting microbial communities, yet their responses to biochemical fulvic acid (BFA) across sodic saline-alkali soils with different textures remain unclear.MethodsA 45-day controlled incubation experiment was conducted using sandy loam and loamy sand amended with BFA at 0, 1, 2, 4, and 8 g kg−2.ResultsResponses to BFA differed between the two soils with different textures and among application rates and were most pronounced during the early incubation period. In sandy loam, 2 g·kg−1 BFA increased ammonium nitrogen and nitrate nitrogen by 68% and 53%, respectively, on day 15 relative to the control. In loamy sand, 1 g·kg−1 BFA increased nitrate nitrogen by 92% on day 15 and ammonium nitrogen by 70% on day 30. Sequencing analysis of soil samples collected on day 45 revealed distinct microbial community responses to 2 g·kg−1 BFA in sandy loam and 1 g·kg−1 BFA in loamy sand.ResultsWithin the conditions of this trial, the optimum application rates were 2 g·kg−1 in sandy loam and 1 g·kg−1 in loamy sand, corresponding to the most remarkable responses.