Ascophyllum nodosum-derived biostimulant promotes physiological conditioning to increase soybean yield in a semiarid climate

The use of algae-based biostimulants as biopromoters for the growth, flowering, and fruiting phases has been intensified in recent years, despite a lack of information about the ideal quantity for maximum efficiency by the plant. This study aimed to select the concentration and application timing of Ascophyllum nodosum-derived biostimulant capable of modulating the physiology and increasing the yield of soybean plants from a semiarid region. The trials were carried out in a greenhouse by applying leaf spraying of biostimulant at 0, 0.5, 1.0 and 1.5 L ha⁻¹, as a single or double application, in different developmental stages (V4, V4 + R1, R1, R1 + R4) of Extrema soybean cultivar. Growth, water content, pollen viability, gas exchange and grain yield were investigated. The biostimulant promoted a better physiological conditioning and productive responses, depending on the dose and application timing. Ascophyllum nodosum-based biostimulant at 1.5 L ha⁻¹, applied 0.75 L ha⁻¹ at V4 + 0.75 L ha⁻¹ at R1 (T12), was the most significant treatment, improving the net photosynthesis, water status and plant growth, which resulted in a 12% increase in grain yield. In conclusion, the dosage and timing of application play pivotal roles in eliciting physiological and productive responses through biostimulants. Seaweed-based biostimulants emerge as essential components to optimizing the cultivation and yield of soybean plants, serving as efficient and sustainable biological regulators.