Seed treatment (or seed coating) is an economical and environment-friendly way for application of functional materials to protect soybean plants from various biotic and abiotic stresses because relatively smaller amounts of material are required for seed treatment compared to foliar spraying or soil drenching. A diverse array of functional (biotic or abiotic) materials can be applied to soybean seeds for the enhancement of plant growth, which can be achieved through various mechanisms, including suppression of pathogens, elevation of nutrient uptake conditions, and production of plant growth hormones. The PI (Dr. Ham)’s laboratory has constructed a large collection of soybean-associated beneficial bacteria (SABBs), which have various types of biological activities for promoting soybean growth. In this project, these bacterial agents are used as the primary materials for seed treatment along with chitosan and biochar, based on the hypothesis that treatment of multiple agents having different beneficial activities would result in additive or synergistic growth-promoting effects. Accordingly, bacterial consortia composed of multiple beneficial bacteria have been tested for their growth-promoting activities in the presence or absence of chitosan and biochar.
Pelletization of fertilizing materials is another way for sustainable management of soybean production because of its several merits, including reduction of nutrient runoffs and leachate water. In this project, pelletizing protocol for the mixture of poultry manure, biochar and chitosan is optimized, and the resultant products are tested for their efficacy in comparison with a commercial fertilizer. Furthermore, beneficial bacterial of soybean are incorporated into the pelletized fertilizers to enhance their fertilizing functions. The overall goal of this project is to develop innovative methods for sustainable production of soybean using beneficial soybean-associated bacteria and functional materials derived from agricultural byproducts (i.e. biochar and chitosan).
Twenty-six bacterial agents were selected among the soybean-associated beneficial bacteria (SABBs) screened based on the laboratory tests for their effects on seed germination and seedling growth of soybean, as well as their antimicrobial activity, IAA production, siderophore production, and extracellular phosphatase activity. Three bacterial consortia (i.e. Set-1, Set-2, and Set-3) were made using multiple bacterial agents derived from the 26 selected bacterial agents, based on the compatibility among the bacterial components. Two of the three bacterial consortia tested (i.e. Set-1 and Set-2) have shown higher growth-promoting activities on soybean plants than any of the individual bacterial agents alone in the greenhouse tests. Meanwhile, three SABBs that previously exhibited excellent growth-promoting activities were tested again in greenhouse and field conditions for validation of their growth-promoting activities. All of the three SABBs showed equivalent or better growth-promoting activities compared to the commercial seed-treating product (fungicide) used for comparison in this project.
Laboratory and greenhouse tests involving pelletized poultry manure, biochar and chitosan were also conducted in 2019. In the laboratory tests using germination pouches, combinational seed treatments with a SABB along with chitosan and biochar or with chitosan and pelletized poultry manure suppressed the disease caused by the artificial inoculation of Rhizoctonia solani at a comparable level with a commercial seed treatment. Pelletized poultry manure also exhibited a better performance of fertilization for soybean growth in greenhouse tests compared with a commercial fertilizer.