Plant biostimulants: innovative tool for enhancing plant nutrition in organic farming

Organic farming has generated significant interest among consumers and scientists owing to their healthier and safer characteristics to human health. However, nutrient (N and P) availability has been identified to be a major yield-limiting factor in many organic farming systems. Plant biostimulants which are defined as substances (humic acids, protein hydrolysates and seaweed extracts) and/or microbial inoculants (plant growth promoting rhizobacteria, arbuscular mycorrhizal fungi and Trichoderma spp.) applied to plants with the aim to enhance plant resilience and also to improve nutrient uptake and translocation. This review focuses on how the plant biostimulants application can overcome nutrient limitation typical of organic systems by improving nutrient availability, uptake and assimilation, and consequently reducing the gap between organic and conventional yields. The agronomical, physiological and molecular responses conferring tolerance to nutrient deficiency were also covered. The review concluded by proposing several research areas to understand the specific application of plant biostimulants to improve the yield of organic horticulture.