Microbial fertilizers and ways to optimize the efficiency of their use in crop production

Biofertilizers represent the most widespread cate­gory of bioproducts in the agricultural market, with steadily increasing demand each year. This review focuses exclusively on classical bioformulations — those that contain live microbial cells. According to market data, nitrogen-fixing microorganisms account for the largest share of global biofertilizer consump­tion (approximately 79%), followed by phosphate-mobilizing microorganisms (around 15%). These figu­res are based on analytical reports from international research agencies and industry market reviews. One of the most well-documented examples of effective microbial use is the inoculation of legume seeds with symbiotic Rhizobium strains. It has been shown that host plants balance the benefits of nitrogen fixation with the carbon costs of nodule formation. To optimize this symbiosis, legumes employ feedback regulation systems (both negative and positive) that respond to infection levels and soil nutrient availability. A loca­lized «nitrogen-sensing» mechanism allows the plant to control the formation of new nodules. Therefore, the application of high doses of mineral nitrogen fer­tilizers can suppress the symbiosis entirely, even when seeds are treated with high-quality bioinoculants. External factors such as soil type, moisture, tempe­ rature, and pH significantly influence Rhizobium activity, nodule development, and nitrogen fixation efficiency. Special attention is given to free-living and associative nitrogen-fixing bacteria, which, in addi­tion to atmospheric nitrogen fixation, offer additional agronomic benefits — improvement of soil structure through the production of exopolysaccharides that bind soil particles and synthesis of phytohormones and biologically active compounds that stimulate chloroplast development and enhance plant stress resistance. The paper highlights the importance of understanding phosphorus dynamics in soil. One of the most promising approaches to increasing phos­phorus availability is the use of phosphate-mobilizing microorganisms. Mechanisms of solubilization of both organic and inorganic phosphates, as well as microbial mobilization of potassium and iron, are described in detail. The potential of siderophore-producing microorganisms is also emphasized. These compoundsen­ hance the uptake of poorly available iron by plants and contribute to the detoxification of soils contami­ nated with heavy metals. Finally, the paper reviews key indicators of microbial biofertilizer efficacy, com­mon application errors, and storage requirements essential for maintaining microbial viability.