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Soybean with bacteria and humics

conditions, offering new ways to enhance microbial implementation challenges relevant to regenerative and
nitrogen fixation. 28,29 climate-smart agriculture.
The effective application of these technologies
depends on the compatibility between microbial 2. Role of nitrogen-fixing bacteria in
strains and customized humic formulations, which sustainable soybean cultivation
must be tailored to specific plant genotypes, soil types,
and environmental contexts. Progress in molecular Recent advances in microbial taxonomy and genomics
genetics—such as the mapping of nodulation genes like have led to the identification of novel nitrogen-fixing
Rj4—has provided tools for breeding soybean cultivars bacterial strains well-adapted to a range of environmental
with enhanced symbiotic capabilities. 30 conditions. For instance, Bradyrhizobium brasilense
Taken together, the integration of humic substances (symbiovar sojae) was isolated from soybean nodules
with microbial biofertilizers presents a scalable, eco- in semi-arid Brazil and exhibited efficient BNF,
friendly solution for sustainable soybean production. highlighting its potential value in dryland agriculture.
33
Successful adoption will require interdisciplinary Inoculation under suboptimal edaphoclimatic conditions
collaboration, standardized application protocols, and has proven effective, especially when paired with
alignment with integrated farm management systems. small amounts of nitrogen fertilizer, often resulting in
This approach also supports circular economy principles synergistic effects on yield. 34
by repurposing agricultural waste into valuable Nitrogen-fixing microbial inoculants include
bio-inputs. Through composting and biochemical both symbiotic bacteria, such as Bj, and free-living
conversion, humic-rich extracts can replace energy- diazotrophs such as Az and Azotobacter (Azb),
intensive synthetic fertilizers, improve soil health, and which enhance soil microbial activity and soybean
contribute to carbon sequestration and water retention. productivity, particularly in nitrogen-limited soils. 35,36
Emerging technologies such as encapsulated These beneficial microbes play an essential role in
inoculants and controlled-release humic formulations improving nitrogen availability where mineral inputs
enable precise input delivery, reduce nutrient loss, are restricted or discouraged.
and enhance efficiency. Furthermore, biotechnological Soil pH is a critical factor affecting inoculant efficacy.
advances such as metabolic engineering and gene editing In acidic soils, formulations that combine rhizobia
are unlocking new possibilities to fine-tune microbial with osmoprotectants have demonstrated improved
performance for diverse environmental conditions. nodulation and higher yields. This is especially
37
Ultimately, the combined use of nitrogen-fixing relevant in marginal lands, including newly converted
microbes and humic substances provides a powerful, pastures and high-latitude regions, where compatible
science-based tool for achieving resilient, productive, native rhizobia populations are often absent. 38
and environmentally responsible soybean cultivation. Co-inoculation strategies, which integrate rhizobia
While previous reviews, such as Maffia et al. and with other PGPB, such as Ps and Streptomyces (St),
31
Canellas et al., have addressed the role of humic further enhance nitrogen fixation, nutrient uptake, and
32
substances and microbial inoculants in plant growth and plant resilience under abiotic stress. Studies conducted
soil health, their focus has primarily been on general in Germany under cool-climate conditions demonstrated
mechanisms of action or specific microbial-humic that specific inoculants improved nodulation and
interactions under controlled conditions. In contrast, nitrogen-use efficiency, resulting in up to 57% increases
this review emphasizes the integrated application of in grain yield and 99% gains in protein yield. 39
nitrogen-fixing bacteria and humic products specifically In tropical, phosphorus-fixing soils such as those in
in soybean cultivation, providing a consolidated Sumatra, rhizobial inoculation significantly increased
framework that spans molecular regulation, agronomic BNF, particularly when combined with liming to
field outcomes, and environmental benefits. Moreover, amend soil pH. This highlights the need for integrated
it offers a comparative synthesis of humic substances soil and microbial management strategies to optimize
derived from agricultural waste and their co-functionality outcomes. 40
with various rhizobacterial strains, contextualized The positive effects of microbial inoculation may
through recent advances in omics technologies, persist across growing seasons. For example, in Scottish
formulation strategies, and sustainability metrics. This soils devoid of compatible native rhizobia, inoculation
approach extends beyond previous meta-analyses by with Bradyrhizobium diazoefficiens resulted in sustained
systematically highlighting field-tested outcomes and nitrogen fixation and doubled soybean grain yield in

Volume 22 Issue 6 (2025) 3 doi: 10.36922/AJWEP025230190