Objective  The stalk fulvic acid (SFA) can be used as a substitute for fulvic acid (FA) and biochemical fulvic acid (BFA), the structure and composition of different fulvic acids and their effects on the growth of wheat are needed to be explored.

  Method  The UV-visible spectrum, fourier transform infrared spectroscopy(FTIR) and ¹³C NMR carbon spectroscopy were used to analyze the structural compositions of different fulvic acids. Using winter wheat GY18204 as material, the effects of different fulvic acids on seed germination and seedling growth of wheat were determined by related indices, such as root length, seedling length, seedling dry weight, root fresh weight and root vigor.

  Result  It is found that the structure of SFA was similar to BFA, but different from FA through the structural analysis. SFA and BFA have more unstable and functional groups, such as polysaccharide and oxygenated aromatic carbon. FA has more stable and less functional groups, such as carboxyl groups. Different fulvic acids can promote the germination of wheat. FA could promote the germination of wheat in a wider range of concentrations. BFA and SFA promoted wheat germination only at low concentrations of 20 and 40 mg L⁻¹ and inhibited it at higher concentrations. The growth of wheat at seedling stage could be promoted by applying fulvic acid after reducing the amount of nitrogen, phosphorus and potassium fertilizer. SFA could increase root length and seedling length by 20-50%, seedling dry weight and fresh root weight by 80-150%, and root activity by 200-240%. FA could increase root length and seedling length by 50-80%, seedling dry weight and fresh root weight by 90-160%, and root activity by 220-250%. In conclusion, controlling the concentration of fulvic acid in the appropriate range can promote the growth of wheat obviously.

  Conclusion  Different sources of fulvic acid have different physical and chemical properties. SFA and BFA with more unstable and functional groups can promote the growth of wheat at a lower concentration, while FA with more stable and less functional groups needs a higher concentration to promote the growth of wheat. The results provide a scientific reference for the exploitation and utilization of stalk resources to prepare fulvic acids and use it as a new biofertilizer for sustainable agricultural production.