Humic Substances in Combination with PGPR

In sustainable agriculture, humic chemicals have been found to be naturally occurring growth boosters. The biological activity of humic substances is influenced by various parameters, including chemical structure, dosage, origin, molecular size, and hydrophobicity. These compounds interact with plants via hormone-like signaling pathways that impact genes, enzymes involved in cell division, nitrogen uptake, and plant development, as well as nutrient transporters, plasma membrane ATPases, and hormone routes. Microorganisms with several functions, including fungi and bacteria, can stimulate the growth of plants. This group of microorganisms associated with plants possess a range of abilities related to plant growth, which can be classified as plant growth–promoting microorganisms, and their functions can be direct or indirect. These abilities improve the availability of nutrients and enhance the capacity of plants to absorb water and nutrients. Additionally, these microorganisms can increase the capacity of plants to perform photosynthesis, boost their tolerance to stress, and reduce the incidence of diseases. Plants support these microbes releasing several energetic molecules through a process named rhizodeposition. These microorganisms colonize the rhizosphere, phyllosphere, and endosphere of plants. These bacteria are benefited by humic chemicals as well, which increase their ability to survive in soil—even in stressful situations. While humic substances (HSs) and plant growth–promoting bacteria (PGPB) have been the subject of several research, little is known about how plants react when both biostimulants—PGPB and HSs—are applied together. An overview of the scientific studies on the application of PGPB and HSs in different crops is given in this chapter. We looked at how these biostimulants affected biological nitrogen fixing and how HSs and beneficial bacteria helped nonleguminous plants develop. Furthermore, covered are the impacts of PGPB and HSs on how plants react to abiotic stressors and their capacity to defend plants against infections. Despite the paucity of research on the function of PGPB and HSs in biocontrol, this strategy may aid in the creation of agricultural biostimulants that are sustainable and ease the shift to sustainable agrosystems.