Alleviation of drought stress in soybean by applying of biostimulant based on amino acids and macro- and micronutrients

Abstract Drought stress is one of the most predominant environmental factors hindering the soybean productivity. This study investigated the effects of an exogenous application of biostimulants, consisting of nitrogen, phosphorous, iron, copper, boron, manganese, zinc and amino acids, in the physiological, biochemical and productive responses of soybean cultivated under drought stress. Findings showed that applying 0.5 kg ha− 1 of the biostimulant improved soybean tolerance to drought. The biostimulant application maintained the leaf photosynthetic rate (A), stomatal conductance (gs), transpiration rate (E), leaf temperature, water use efficiency (WUE) and carboxylation efficiency (CE), in addition to increasing the SPAD index. Moreover, the biostimulant heightened the activity of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) and maintained the activity of the nitrate reductase enzyme. Regarding osmoprotectant, the biostimulant application enhanced proline accumulation, which could improve the soybean’s osmotic adjustment under drought conditions. In addition, foliar application of the biostimulant maintained the biometric and production characteristics, stem diameters, number of branches, number of pods with 1, 2 and 3 grains, and significantly increased leaf area, number of primary stem nodes, dry matter mass in the aerial part and roots, ultimately increasing yield. Based on the aforementioned beneficial properties, the biostimulant based on macro- and micronutrients and amino acids, particularly in the dose 0.5 kg ha− 1, has proven to effectively relieve the adverse effects of drought stress in soybean.