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Syromiatnykov

the 2 year. In addition, introduced strains were still Latvia also demonstrated that inoculation with diverse
nd
detectable in the soil, suggesting long-term ecological microbial consortia—including St, Paraburkholderia,
integration. 41 and Ps—increased nodule-associated bacterial diversity
In the context of conservation agriculture and organic and plant growth-promoting traits, further confirming
farming, inoculation-induced BNF contributes to long- the synergistic effects of integrating nitrogen-fixing
term soil fertility by increasing organic matter content bacteria with humic substances under real-world
and enhancing nitrogen cycling—key components of conditions. 48
sustainable land management. 42-47 Table 1 presents a comparative overview of nitrogen-
Figure 1 presents soybean productivity under four fixing bacterial strains, environmental conditions,
treatment conditions—inoculated, baseline, humic only, inoculation strategies, and their agronomic effects in
and combined treatment—across five bacterial strains sustainable soybean cultivation.
abbreviated as Bj, Az, Azb, Ps, and St. The inoculated Bj, when applied through single or co-inoculation
treatment displayed productivity values of 90% for Bj, under neutral to slightly acidic soils and supplemented
75% for Az, 65% for Azb, 60% for Ps, and 55% for St. with humic acids or lime, increases nodulation by up
In comparison, the baseline (control) values are lower: to 40% and enhances soybean grain yield by 20–30%.
70% for Bj, 65% for Az, 60% for Azb, 55% for Ps, and BNF under these conditions improves by approximately
50% for St. The humic-only treatment yields moderate 25–35%.
gains, with 75% for Bj, 68% for Az, 64% for Azb, 58% In cooler climates, such as those found in northern
for Ps, and 52% for St. Notably, the combined treatment Europe, inoculation with B. diazoefficiens in soils
(inoculants + humics) results in the highest productivity lacking compatible native rhizobia has resulted in a
across all strains, reaching 95% for Bj, 85% for Az, 78% twofold increase in grain yield. In addition, residual
for Azb, 72% for Ps, and 68% for St. These data indicate soil nitrogen levels remain higher, suggesting the long-
that the combined application consistently outperforms
other treatments, delivering up to 25–30% higher term ecological integration of the introduced microbial
productivity than the control. Notably, field trials in strains.
Free-living and associative bacteria such as
Azospirillum brasilense contribute to enhanced protein
content in soybean seeds (by 15–20%) and promote
root development, particularly in nitrogen-deficient
soils. Similarly, Azotobacter spp., applied in acidic or
marginal environments, improve soil microbial activity
and plant vigor, resulting in yield increases of 10–15%,
especially when co-applied with humic substances.
In temperate and cold regions, Ps spp. used in
co-inoculation approaches improves nitrogen-use
efficiency, increasing nutrient uptake by 18–25%. In
saline or degraded soils, St spp. combined with chelated
Figure 1. Comparative effects of bacterial and iron and polymer-based additives enhance nodulation
humic treatments on soybean productivity. Bars and chlorophyll content, leading to improvements in
represent the relative productivity index (%) for five photosynthesis and plant growth by 20–30%.
bacterial strains: Bradyrhizobium japonicum (Bj), In tropical regions with acidic soils, indigenous
Azospirillum (Az), Azotobacter (Azb), Pseudomonas Bradyrhizobium strains used with lime and compost
(Ps), and Streptomyces (St). Treatments include have been demonstrated to increase nitrogen fixation
baseline (control), humic only, inoculated, and by 35–40%, owing to improved microbial compatibility
combined (inoculants + humics). Data are presented and soil pH buffering.
as mean ± standard deviation (n = 3). Asterisks (*) Overall, Table 1 illustrates that tailored combinations
indicate statistically significant differences from of nitrogen-fixing bacteria, inoculation strategies, and
the baseline at p<0.05. Combined application supportive amendments can lead to significant gains
consistently displayed the highest productivity in soybean productivity—often ranging between 20%
values, highlighting the synergistic effect of humic and 60%—depending on environmental context and
substances and nitrogen-fixing bacteria. microbial compatibility.

Volume 22 Issue 6 (2025) 4 doi: 10.36922/AJWEP025230190