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Soybean with bacteria and humics

Table 4. Environmental and agronomic benefits of combining humic products with nitrogen-fixing
bacteria in soybean cultivation

Benefit type Effect Quantitative impact References
Soil health Improved organic matter stabilization, enhanced ↑ Soil organic carbon by 15–20% 31,78
aggregate formation
Nutrient Enhanced nitrogen and iron uptake through chelation ↑ N use efficiency by 25–35%, ↑ 65,83
efficiency and root expansion Fe uptake by 20%
Nitrogen loss Reduced nitrate leaching and ammonia volatilization ↓ N loss by up to 40% 78,79
control through microbial N assimilation
Abiotic stress Increased drought, salinity, and acidity resistance due ↑ Yield under drought by 25–30%, 50,80,82
tolerance to hormonal and redox regulation ↑ chlorophyll content
Soil microbiota Stimulated beneficial microbial communities and ↑ Rhizosphere diversity, ↑ residual 42,62
rhizobial persistence inoculant strains
Carbon Enhanced humification and reduced need for ↑ Carbon input retention; ↓ GHG 25,31,85
sequestration synthetic N inputs emissions
Sustainability and Alignment with organic standards and circular Accepted under eco-labeling 84,85
policy economy goals schemes
Abbreviation: GHG: Greenhouse gas emissions.

While the temporary suppression of plant immune However, overstimulation of immune tolerance
signaling is essential for the successful establishment may inadvertently reduce the plant’s defense readiness
of rhizobial symbiosis, concerns have been raised against certain pathogens. While humic substances and
about increased susceptibility to pathogens during beneficial microbes often prime antioxidant and signaling
this window. However, most studies have not reported pathways, excessive suppression of jasmonic acid or
a significant rise in disease incidence following salicylic acid responses may facilitate opportunistic
co-inoculation. On the contrary, humic substances infections under high pathogen pressure. For instance,
have been demonstrated to induce systemic resistance Canellas et al. reported that co-application with
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and modulate defense-related metabolic pathways, certain humates reduced resistance to Fusarium spp.
potentially compensating for localized immune in stress-prone environments. These findings suggest
suppression. For instance, Canellas et al. noted that immunomodulation strategies must balance growth
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enhanced phenolic compound biosynthesis and promotion with adequate pathogen surveillance.
reactive oxygen species (ROS)-scavenging enzyme To address the current lack of standardization in
activity in humate-treated plants, both linked to humic product characterization, future studies should
improved resilience against fungal pathogens. adopt specific analytical protocols that enable reliable
Nonetheless, field-level quantification of pathogen product quality assessment and cross-comparison.
trade-offs remains scarce and warrants further study Recommended procedures include the determination
under variable climatic and edaphic conditions. of elemental carbon-to-nitrogen (C/N) ratios, which
For example, Canellas et al. reported increased provide insights into the degree of humification
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susceptibility of soybean plants to Fusarium spp. in and microbial stability. Spectroscopic techniques,
soils amended with high doses of humic acids under such as Ultraviolet-visible (UV-Vis) spectroscopy,
greenhouse conditions, suggesting that excessive Fourier-transform infrared spectroscopy (FTIR),
suppression of plant immune signaling may inadvertently and C-nuclear magnetic resonance (C-NMR), can
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facilitate pathogen colonization. Similarly, Pisarek be employed to identify key functional groups and
and Grata observed a mild increase in foliar disease molecular structures associated with biological activity.
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incidence in organic soybean systems where humic-rich In addition, redox potential measurements and solubility
composts were applied without microbial antagonists. fractionation (e.g., alkaline extraction followed by acid
These findings highlight the importance of balanced precipitation) may serve as proxies for estimating the
application rates and, where feasible, the co-application oxidative reactivity and fraction composition (humic
of biocontrol agents to reduce pathogen risks associated acid vs. fulvic acid) of the material. The adoption of
with immunosuppression. such protocols could improve reproducibility, facilitate

Volume 22 Issue 6 (2025) 11 doi: 10.36922/AJWEP025230190