The study researches on plant production with particular attention to the environment. It first mentions the usage of ascorbic acid for depolymerization of carrageenans from dry K. alvarezii biomass, its hydrolysate’ characteristics, and its positive influence on the hybrid maize crop in Vietnam. The study is one of the very fewer studies evaluating the plant-growth promoting activity of oligocarrageenans on maize crops. The results of the study introduce an oligocarrageenans-rich biostimulant prepared by acid hydrolysis of K. alvarezii seaweed in ascorbic acid, and positive impacts of foliar spraying of the hydrolysate (at different Mw of oligocarrageenans and concentrations) on the hybrid maize crop in Vietnam. The application of this product resulted in increases in efficiency of nutrient uptake by the plant, plant height (~20. 6%), and grain yield (by 21.3% over the control). Therefore, it is suitable for application on a large scale agriculture to reduce the chemical fertilizers used