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Syromiatnykov

increased auxin-like activity and antioxidant enzyme in enhancing BNF and productivity when combined
responses in co-treated soybean plants, contributing to with inoculants. These results highlight the superior
higher photosynthetic rates and yield components. 70,71 performance of Bj and Az under co-application with
In acidic soils where aluminum toxicity restricts humic substances, supporting their role in enhancing
nodulation, humic substances chelate toxic ions and nitrogen fixation and plant growth efficiency.
buffer pH, enabling better survival and effectiveness Table 3 summarizes the synergistic effects observed
of acid-tolerant Bradyrhizobium strains. These actions when humic substances are co-applied with nitrogen-
restore the root zone microenvironment and facilitate fixing bacteria under different stress conditions in
robust symbiosis even in marginal lands. 72-74 soybean cultivation. For example, applying humic acid
Furthermore, the co-inoculation approach reduces with Bj in acidic soils (pH < 5.5) increased nodulation
reliance on synthetic fertilizers by boosting internal by 30–40% and yield by 20–25%. 49,72,74 Under drought
nitrogen supply through improved BNF. In multiple stress, fulvic acid combined with A. brasilense
field trials, humic-enhanced inoculants have led to enhanced root biomass by 25%, photosynthetic rate by
increased grain yield, seed protein content, and residual 15%, and grain yield significantly. 50,70,71 . In compacted
soil nitrogen—benefits that extend into subsequent or oxygen-poor soils, humin with Bradyrhizobium
cropping cycles. 75 and Herbaspirillum improved nitrogenase activity
Precision delivery systems, such as humic-coated by 35% and raised seed protein content. 28,72 A mix of
granules and encapsulated inoculants, offer additional humic and fulvic acids with St and B. japonicum in
advantages by protecting microbial viability during saline soils improved germination by 20% and shoot
storage and application. These controlled-release nitrogen concentration. 48,51 Artificial humic acids
formulations ensure better synchronization between with Bradyrhizobium-Ps consortia under semi-arid
microbial activity and plant demand. 76 conditions increased grain yield by 30–40% and left
Together, humic products and nitrogen-fixing more residual nitrogen in the soil. 65,66 The use of humic-
bacteria represent a potent agroecological input pair coated inoculants improved microbial survival and
that enhances productivity, promotes resilience, and long-term BNF, boosting crop resilience in organic
contributes to long-term soil health, making them vital systems. 35,75,77 Finally, vermicompost-derived humates
tools in climate-smart and organic farming systems. applied with mixed PGPR enhanced biomass by
Soybean productivity is expressed in normalized units 20–30% and nutrient uptake on degraded lands. 59,61,62
(index scale: 0–100) based on the relative contribution These results demonstrate that targeted combinations
of each microbial strain to grain yield in co-application of humic substances and microbes significantly improve
trials (Figure 3). Bj displays the highest impact (95 soybean growth and stress tolerance across diverse
units; 23.9% of total), followed by Az (85 units; 21.4%), environments.
Azb (78 units; 19.6%), Ps (72 units; 18.1%), and St (68
units; 17.1%). These values reflect compiled trial data 5. Environmental and agronomic benefits of
and emphasize the synergistic role of humic substances integrated biotechnologies

In terms of ecosystem services, the integrated use
of humic substances and nitrogen-fixing bacteria
contributes to the stabilization of soil organic matter and
improved aggregate structure—key indicators of soil
health and carbon sequestration capacity. These effects
are especially valuable in conservation agriculture,
where minimal soil disturbance and residue retention
are practiced.
Some studies reported that nitrate leaching could
be reduced by up to 40% through the co-application
of humic substances and nitrogen-fixing inoculants.
This effect is attributed to improved nitrogen retention
Figure 3. Contribution of nitrogen-fixing bacteria to in the root zone, enhanced microbial assimilation, and
soybean productivity under combined application stimulation of plant uptake pathways. For example,
with humic substances Maffia et al. demonstrated a 35–40% reduction
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Volume 22 Issue 6 (2025) 8 doi: 10.36922/AJWEP025230190