Humic Acid: Boosting Soil and Plant Resilience Against Stress

Humic acid (HA), a decomposition product of organic matter, is the key component of humic substances (HSs). It plays a pivotal role in enhancing soil structure, nutrient availability, and plant growth. The complex molecular composition of HA enables it to chelate nutrients, buffer the soil pH, and improve water retention. HA acts as a biostimulant, stimulating root architecture, enzyme activity, and hormone signalling pathways, thereby improving nutrient acquisition and stress tolerance in plants, and therefore, necessitates its application in crop production. HAs can be applied in different methods—foliar sprays, seed treatments/priming, and soil incorporation, while their efficacy depends on crop types, soil conditions, and environmental stresses (salinity, drought, extreme temperature, waterlogging, and heavy metal contamination). Additionally, HAs enhance plant defence against biotic stresses (insects and diseases) by altering microbial communities and inducing resistance-related genes. HAs also show promise in environmental and industrial applications. Overall, the multifunctional properties of HA make it a sustainable tool for improving crop productivity and ecological resilience.