Objective  To reveal the effect of humic acid alkaline fertilizer on banana growth and its promotion mechanism, and provide a theoretical basis for the development, popularization and application of the humic-acid alkaline fertilizer.

Method  Banana pot experiment was carried out. Banana biomass, soil microorganism, enzyme activity, root activity, soil nitrogen and phosphorus nutrient content were measured to identify the efficacy of humic acid alkaline liquid fertilizer.

Result  Compared with conventional compound fertilizer and non-humic-acid alkaline liquid fertilizer, humic acid alkaline fertilizer could promote banana growth and biomass, increase root activity. The soil urease and acid phosphatase activities, soil mineral nitrogen and available phosphorus content, number of bacteria, fungi and actinomyces increased obviously. Leaf area and biomass increased by 50–100 cm² and 10%–21%, respectively. The root activity increased by 89%–188%. Soil urease and acid phosphatase activity increased by 25%–91% and 2.4–3.5 times, respectively. The number of soil bacteria, fungi and actinomycetes of humus-acid alkaline liquid fertilizer were 1.6–14.4, 1.7–26.7 and 2.3–3.8 times those of compound fertilizer treatment, respectively. The corresponding data of the humus acid alkaline liquid fertilizer were 3.0–10.6, 3.9–56.0 and 1.2–2.0 times of those of alkaline liquid fertilizer without humus acid, respectively.

Conclusion  Application of humic acid alkaline liquid compound fertilizer could obviously promote banana growth. The mechanism was that the acidic soil environment was improved by the alkaline fertilizer and then the soil microbial diversity increased on the one hand; The humic acid increased soil urease and acid phosphatase activities, the soil nitrogen and phosphorus nutritional status were improved on the other hand to increase soil fertility. Therefore, the synergistic application of humic acid and alkaline liquid fertilizer is a rational measure to supply nutrients to banana and improve soil fertility.