Natural Biostimulants for Sustainable Agriculture: The Mechanisms and Functions of Humic Substances for Plant Growth Advancement

Humic substances (HS) are important parts of soil organic matter and are very important for the health of the soil, the growth of plants, and the soil's ability to withstand both biotic and abiotic pressures. HS are used a lot in sustainable farming because they have several different physicochemical qualities that make them useful for things such as soil conditioning, nitrogen management, and biostimulation. This review compiles existing information regarding the structure, origin, and methods of action of HS, focusing specifically on its impact on soil characteristics, nutrient availability, plant growth, and resilience to stress. Recent advancements in extraction, characterization, and application methodologies are examined, alongside novel notions that regard HS as supramolecular assemblies rather than distinct macromolecules. The paper talks about the main problems with HS heterogeneity, extraction artifacts, and standardization. It also points out the most important research areas that might help make HS safer and more effective in agriculture and related fields.