The composition of biostimulants applied in seed treatment interferes with the soybean emergence under water deficiency

High physiological quality seeds with high germination and vigor are essential for successful soybean (Glycine max L. Merrill) cultivation, ensuring proper establishment and early development. Biostimulants have shown significant potential to enhance soybean performance, especially under environmental stress, such as water deficit, which impairs germination and emergence. This study evaluated the effects of seed treatments with biostimulants and their interaction with insecticide and fungicide on biometrics, nutrition, and biochemical variables during soybean initial development under water deficit conditions. A randomized block design in an 8×2 factorial scheme was employed, comprising eight seed treatments [control (no biostimulant); Imidacloprid and fungicide (Carboxin + Thiram) (IF); three biostimulants (B1, B2, B3); and their combinations with IF] under two water regimes (100% and 50% of pot capacity), with three replicates. Evaluations 21 days after application included germination, emergence speed, root and shoot length, dry matter, and enzymatic activity. Biostimulants, particularly seaweed- and plant extract-based, improved water deficit tolerance, enhancing germination, emergence, biometrics, enzymatic activity (superoxide dismutase, peroxidase, and catalase), and nutrient uptake (P, K, Mg, Cu, Mn, Zn). However, further studies are needed to assess potential adverse interactions between biostimulants, fungicides, and insecticides.