Page 7 - AJWEP-22-6

Asian Journal of Water, Environment and Pollution. Vol. 22, No. 6 (2025), pp. 1-20.
doi: 10.36922/AJWEP025230190

REVIEW ARTICLE

Sustainable soybean cultivation using nitrogen-fixing
bacteria and humic products derived from agricultural

waste: A review

Yurii Syromiatnykov*
Institute of Soil and Plant Sciences, Faculty of Agriculture and Food Technology, Latvia University of Life Sciences and
Technologies, Jelgava, Zemgale Region, Latvia
*Corresponding author: Yurii Syromiatnykov (yurii.syromiatnykov@lbtu.lv)

Received: June 8, 2025; Revised: July 9, 2025; Accepted: July 16, 2025; Published online: August 27, 2025

Abstract: Sustainable intensification of legume-based cropping systems requires innovative strategies that enhance
nitrogen fixation and nutrient use efficiency while minimizing environmental impacts. This review examines the
co-application of nitrogen-fixing bacteria and humic substances derived from agricultural waste as an integrated
biotechnological approach to support sustainable soybean production. The review also summarizes key roles of
microbial inoculants, such as Bradyrhizobium, Azospirillum, and Pseudomonas (Ps), and the agronomic functions
of humic acids, fulvic acids, and humin compounds. When applied separately, these biostimulants improve
nodulation, nutrient uptake, and soil health. When combined, they demonstrate synergistic effects—improving
nitrogen-use efficiency, drought tolerance, and crop yield. Mechanisms driving these outcomes include enhanced
microbial colonization, micronutrient chelation, hormonal modulation, and antioxidant activity. In addition, the
review considers challenges including soil pH variability, native microbial competition, product standardization,
and formulation compatibility. Recent advances in encapsulated inoculants and hydrothermal humification
methods demonstrate promise for improving bioavailability and resilience. Environmental benefits include reduced
nitrate leaching, increased soil organic matter, and alignment with circular bioeconomy principles through the
valorization of organic waste. Despite barriers, such as formulation variability, limited precision delivery systems,
and regulatory gaps, the integration of microbial and humic inputs offers a scalable, eco-friendly alternative to
synthetic fertilizers. Future research should focus on molecular characterization, genotype-strain matching, and
long-term field validation to ensure robust performance across agroecological zones. Finally, this review provides
a comprehensive synthesis for researchers, agronomists, and policymakers seeking to improve the ecological and
economic sustainability of soybean production through advanced biotechnological interventions.

Keywords: Nitrogen-fixing bacteria; Humic substances; Soybean; Biological nitrogen fixation; Sustainable
agriculture; Microbial inoculants

1. Introduction symbiotic relationships with nitrogen-fixing bacteria
that convert atmospheric nitrogen into plant-available
Soybean (Glycine max) is globally valued not only forms. This process, known as biological nitrogen
for its nutritional content but also for its critical role fixation (BNF), significantly reduces the need for
in sustainable agriculture. As a legume, soybean forms synthetic nitrogen fertilizers, thereby decreasing

Volume 22 Issue 6 (2025) 1 doi: 10.36922/AJWEP025230190