Application timing of Ascophyllum nodosum extract enhances soybean growth and yield under field conditions

Seaweed extracts, particularly those derived from Ascophyllum nodosum, have emerged as promising biostimulants capable of enhancing crop performance and resilience. This study evaluated the effects of application timing of A. nodosum extract on the agronomic performance and yield of soybean under field conditions in two locations in Paraná, Brazil (Londrina and Luiziana). Four treatments were tested: control (CON), application at sowing (SEM), foliar application 20 days after sowing (20D), and combined application at sowing and 20 DAS (S20). Growth parameters, nodulation, root traits, yield components, and productivity were assessed. In Londrina, the S20 treatment increased productivity by 1.45 times compared to CON, with gains of 1,546 kg ha⁻¹. In Luiziana, where co-inoculation with Bradyrhizobium spp. and Azospirillum brasilense was performed, 20D resulted in the highest yield (5,721 kg ha⁻¹), corresponding to a 23.7% increase over CON. Significant improvements in the number of viable nodules, pods, grains per plant, and shoot biomass were observed, particularly in combined applications. These findings indicate that A. nodosum extract enhances root and shoot development, nodulation, and yield, especially when applied during early vegetative stages. The results highlight the potential of integrating seaweed biostimulants with biological inoculants as a sustainable strategy for improving soybean productivity.