Objectives This study investigated the effects of fulvic acid fertilize application on rhizosphere soil microorganisms and soil enzymes with wheat, providing theoretical and data reference for the research and application of fulvic acid fertilizer.

Methods In this study, wheat was used as the experimental crop and the application amount of fulvic acid fertilizer (20.6% fulvic acid content) was 0, 2, 6 and 10 g/kg. All treatments except CK were applied with the same amount of compound fertilizer (15–10–20). After the seeds were thinly covered with soil, the fulvic acid fertilizer that was needed for treatment was applied. After 40 days of wheat sowing, wheat rhizosphere soil was collected, and the number of soil microbial population was determined by dilution plate smear method, microbial functional diversity was determined by biolog-eco ecological plate, and soil enzyme activity was determined by conventional method.

Results Within the application of 0 and 2 g/kg fulvic acid fertilizers, the germination rate of wheat seeds was 100%. However, the seed germination rate decreased about 3%, 9% when the application of fulvic acid fertilizer was 6 and 10 g/kg. There was no significant difference among the four treatments. With the application of fulvic acid fertilizer on the basis of compound fertilizer, the number of bacteria, fungi and actinomycetes in soil increased significantly, and finally reached the maximum when the application amount of fulvic acid fertilizer reached 6 g/kg. The activity of four soil enzymes was promoted by fulvic acid fertilizer, especially for catalase, which was found the most significant effect. And the activities of urease, acid phosphatase, catalase and sucrase in wheat rhizosphere soil reached the maximum when the application amount of fulvic acid fertilizer reached 10 g/kg. Within the application of 6 g/kg, 10 g/kg fulvic acid fertilizer, the overall activity of soil microorganisms, species richness and evenness, diversity of community, and the respiration intensity of rhizosphere soil microorganisms were increased significantly. And when the application of fulvic acid fertilizer reached 10 g/kg, the best effect was obtained.

Conclusions The research showed that the application of fulvic acid fertilizer within the 40 days experiment period increased effectively bacteria, fungi and actinomycetes in soil, improved significantly the function of microbial population, and increased the activity of urease, acidic phosphatase, catalase and sucrose enzyme. However, significant results were achieved only when fulvic acid fertilizer was applied up to 6 g/kg.