Cu(II)-Based Water-Dispersible Humic Acid: Synthesis, Characterizations, and Antifungal and Growth-Promoting Performances

The complex synthesis process, low utilization, and single function of fungicides have seriously hindered the development of fungicides in resistance to rice sheath blight. Here, an inexpensive and multifunctional Cu(II)-based water-dispersible humic acid (Cu-WH) fungicide with growth-promoting ability was developed with a simple method. A 3D molybdate carbon hierarchical nanosphere (MoO2-C-HN) catalyst was successfully synthesized using a green route and applied in a solid-phase activation of lignite to obtain water-dispersible humic acid. Cu(II)-based water-dispersible humic acid (Cu-WH) was then formed through a simple reaction of Cu(II) and the humic acid. The resultant Cu-WH showed strong antifungal performance against Rhizoctonia solani in laboratory incubation experiments. After being treated with Cu3-WH (0.1 mg L–1), the control efficiency of rice sheath blight at 1, 3, and 5 days after infection was 90.54%, 78.96%, and 66.31%, respectively. It also enhanced the water-holding capacity of the substrate and thus effectively improved the growth of rice seedlings. In comparison to commercial rice seedling substrate, the substrate treated with 8 wt % of Cu3-WH increased plant height, stem diameter, fresh weight, and chlorophyll content by 19.23%, 35.91%, 14.52%, and 42.85%, respectively. The newly developed Cu-WH thus can be used as a novel low-cost efficient fungicide and growth stimulator to treat rice sheath blight as well as to increase rice production.