Humic Extract as a Biostimulant in Crops Subjected to Abiotic Stress

Abstract

Because abiotic stresses pose significant challenges to the growth and productivity of crops, the development of plants with greater survival and growth when exposed to unfavorable situations is an objective of several research groups. Biostimulants are substances or microorganisms that, when applied to crops through the foliar or root pathways, serve to enhance various processes related to growth and development. These processes include nutrient absorption, tolerance to environmental stress, and overall harvest quality. Interestingly, biostimulants can achieve these effects even when they possess a low concentration of nutrient elements in their composition. Among the main and most often used biostimulants are plant hormones, algae extract, mycorrhizal fungi, protein hydrolysates, and humic substances (humic and fulvic acids). This review sheds light on the biostimulant effects of applying humic substances to plants experiencing hydric stress conditions and low rainfed cultivation. Additionally, it aims to identify gaps in the current research and highlights areas that require further investigation. Furthermore, the review provides a concise overview of the origin and progression of research on humic substances (HS), including their extraction and obtaining process, as well as their structural characteristics and the relationship between structure, properties, and functions. The review also presents the research findings that support the potential of humic substances influencing crops affected by abiotic stress. These findings highlight the beneficial effects of humic substances in enhancing the resilience and performance of crops facing challenges such as drought, salinity, temperature extremes, and other non-biological stressors. The evidence underscores the significance of humic substances as a valuable tool in mitigating the detrimental impacts of abiotic stress on crop productivity and overall plant health.