Seed treatment with biostimulant doses in soybean development and gas exchange

Soybean is an essential agricultural product in Brazil, being the world leader in production and exportation. The use of biostimulants, such as Humic Substances (HS), can induce physiological responses that stimulate plant development. However, few studies address the use of seed treatment, and when associated with soybean culture, they are almost nonexistent. Thus, the objective was to evaluate the responses of applying HSs in seed treatment on the morphology and physiology of soybean plants, cultivar OLIMPO 80I82RSF IPRO. The study was conducted with five doses of HS (0; 2; 4; 6; and 8 mL kg-1 of seeds) applied in seed treatment, arranged in a completely randomized design, with five replications. The HS was extracted from ruminal compost with KOH and applied directly to the seeds. The crop was cultivated until the V7 stage, and variables on morphology, biomass, and physiology were measured and evaluated by analysis of variance (p ≤ 0.05) with models adjusted by polynomial regressions. There was a positive response at the dose of 4 mL kg-1, mainly on plant height, dry shoot mass, CO2 assimilation rate, and stomatal conductance compared to the zero dose. As for dry mass and root volume, the 6 mL kg-1 dose had a greater influence compared to the zero dose. These results demonstrate that HSs associated with seed treatment enhance soybean crop development.