The increasing need for environmentaly friendly agricultural practices is driving the use of fertilizers based on beneficial microorganisms. The latter belong to a wide array of genera, classes, and phyla, ranging from bacteria to yeasts and fungi, which can support plant nutrition with different mechanisms. Moreover, studies on the interactions between plant, soil, and the different microorganisms are shedding light on their interrelationships thus providing new possible ways to exploit them for agricultural purposes. However, even though the inoculation of plants with these microorganisms is a well-known practice, the formulation of inocula with a reliable and consistent effect under field conditions is still a bottleneck for their wider use. The choice of the technology for inocula production and of the carrier for the formulation is key to their successful application. This paper focuses on how inoculation issues can be approached to improve the performance of beneficial microorganisms used as a tool for enhancing plant growth and yield.

The application of plant beneficial microorganisms has been widely accepted as an efficient alternative to chemical fertilizers and pesticides. Isolation and selection of efficient microorganisms, their characterization and testing in soil-plant systems are well studied. However, the production stage and formulation of the final products are not in the focus of the research, which affects the achievement of stable and consistent results in the field. Recent analysis of the field of plant beneficial microorganisms suggests a more integrated view on soil inoculants with a special emphasis on the inoculant production process, including fermentation, formulation, processes, and additives. This mini-review describes the different groups of fermentation processes and their characteristics, bearing in mind different factors, both nutritional and operational, which affect the biomass/spores yield and microbial metabolite activity. The characteristics of the final products of fermentation process optimization strategies determine further steps of development of the microbial inoculants. Submerged liquid and solid-state fermentation processes, fed-batch operations, immobilized cell systems, and production of arbuscular mycorrhiza are presented and their advantages and disadvantages are discussed. Recommendations for further development of the fermentation strategies for biofertilizer production are also considered.

High soil acidity and elevated soil Al concentrations limit plant growth in many terrestrial ecosystems. Aluminium toxicity can be ameliorated by Ca. Thus, Ca/Al molar ratios in soil solution and in plant tissues have been proposed as superior indicators than Al concentration itself for evaluating the Al toxicity stress to trees (Cronan & Grigal, J Environ Qual 1995 Cronan, C S and Grigal, D F . 1995. Use of calcium/aluminum ratios as indicators of stress in forest ecosystems. J Environ Qual, 24: 209–226. [Crossref], [Web of Science ®] [Google Scholar] ;24:209 – 226). This article presents an overview of publications since 1995 where the reduced Ca/Al ratio in fine tree roots has been used as an indicator of stress for Al and/or soil acidity. The main aim of this review was to evaluate the use and the critical threshold of the fine root Ca/Al ratio as a potential indicator for Al toxicity stress to trees in acid soils. Based on the reviewed literature, the fine root Ca/Al molar ratio was strongly negatively related to Al stress in small tree seedlings in controlled environments, whereas the response was not clear under field conditions where other environmental factors interact. Fine root Ca/Al ranged from 0.03 to 17 in tree seedlings and from 0.1 to 18 in mature trees depending on experimental and site conditions, as well as the tolerance and uptake mechanisms of the different tree species. Fine root Ca/Al was positively related to the soil solution Ca/Al molar ratio. Fine root Ca/Al ratios were related positively to fine root length, growth, specific root length, and biomass, and negatively to root diameter, callose formation, respiration chain activity, starch concentration, and root necromass. A number of relationships have been also found between the fine root Ca/Al and above-ground seedling and/or mature tree growth and nutrient uptake. The critical thresholds for the Ca/Al fine root ratio of 0.2 suggested by Cronan and Grigal ( 1995 Cronan, C S and Grigal, D F . 1995. Use of calcium/aluminum ratios as indicators of stress in forest ecosystems. J Environ Qual, 24: 209–226. [Crossref], [Web of Science ®] [Google Scholar] ) is estimated to represent 90% risk of inverse impact on root and above-ground tree growth. Values of Ca/Al molar ratio in the fine roots of mature trees were only rarely determined below the critical 0.2. The caveats for the use and the interpretation of Ca/Al ratio in fine roots have been addressed in detail. A protocol for root processing and elemental analysis to obtain reliable and comparable results of Ca and Al concentrations in roots is also provided. The article concludes with recommendations for a wider use of the Ca/Al ratio in roots as a bioindicator of Al toxicity to trees in acid soils.

Key priorities in biochar research for future guidance of sustainable policy development have been identified by expert assessment within the COST Action TD1107. The current level of scientific understanding (LOSU) regarding the consequences of biochar application to soil were explored. Five broad thematic areas of biochar research were addressed: soil biodiversity and ecotoxicology, soil organic matter and greenhouse gas (GHG) emissions, soil physical properties, nutrient cycles and crop production, and soil remediation. The highest future research priorities regarding biochar’s effects in soils were: functional redundancy within soil microbial communities, bioavailability of biochar’s contaminants to soil biota, soil organic matter stability, GHG emissions, soil formation, soil hydrology, nutrient cycling due to microbial priming as well as altered rhizosphere ecology, and soil ph buffering capacity. Methodological and other constraints to achieve the required LOSU are discussed and options for efficient progress of biochar research and sustainable application to soil are presented.

A two-year (2020–2021) field experiment was conducted to investigate the impact of particular nanoparticles and biofertilizers on the growth, yield, and biochemical attributes of peanuts (Cv. Giza 6). Before planting, the seeds were inoculated with two biofertilizers, mycorrhiza and phosphorine, and were considered the main plot. The subplot contained foliar sprays of nanoparticles, i.e., 200 ppm boron (B), 200 ppm calcium (Ca), their combination (Ca+B), and the control (no spray). The results revealed that mycorrhiza significantly increased 100-seed weight (70.45 g), seed yield (1.9 ton/ha), biological yield (7.5 ton/ha), crop growth rate (CGR) (2.9 g day⁻¹ m⁻²), branching number (12.5), and protein content (22.96) compared with the control or phosphorine. Among the nanoparticles, Ca+B maximally improved plant height, CGR, 100-seed weight, shelling percentage, seed yield, oil content, and seed protein, while plants treated with B exhibited maximum seed nitrogen, pods per plant, and biological yield compared to other treatments. Overall, plants treated with Ca and B nanoparticles and mycorrhiza exhibited remarkable improvement in their growth, yield, and biochemical attributes, suggesting that nanotechnology and biofertilization are steps toward environmentally friendly, progressive farming. This study laid the basis for further elucidation of the molecular mechanism of plants in response to these nanoparticles and biofertilizers.

Due to the impoverishment of agricultural and horticultural soils and replant diseases, there is a need to use bioproducts and beneficial microorganisms in order to improve the quality of soils and growth substrates. For this reason, research was undertaken to assess the impact of arbuscular mycorrhizal fungi and rhizosphere bacteria on changes in soil microbiology, the degree of colonization of plant roots by mycorrhizal fungi, selected physiological parameters, and fruit quality and yield of the strawberry cultivar “Rumba.” The plants were inoculated with the mycorrhizal preparation Mykoflor (Rhizophagus irregularis, Funneliformis mosseae, Claroideoglomus etunicatum), MYC 800 (Rhizophagus intraradices), and the bacterial preparation Rhizocell C (Bacillus amyloliquefaciens IT45). The applied preparations increased the total number of bacteria and fungi in the soil and mycorrhizal frequency in the roots of the strawberry plants. They increased the chlorophyll “a” and total chlorophyll concentrations in the leaves as well as the rate of transpiration and CO₂ concentration in the intercellular spaces in the leaves. The plants treated with Rhizocell C and MYC 800 exhibited a higher CO₂ assimilation rate than control plants. The biopreparations increased chlorophyll fluorescence parameters such as maximum fluorescence (F_M) and the maximum potential photochemical reaction efficiency in PS II (F_V/F_M). The influence of the species of rhizosphere bacteria and mycorrhizal fungi used in the experiment on the physiological traits of strawberry plants contributed, especially in the second year of the study, to increase the yield and mean weight of strawberry fruit.