High School Student Poster Session

[HS-P03] Improving Nitrogen Use Efficiency through Rhizobium Symbiosis: Effects of Inorganic Nitrogen Conditions on Soybean Growth and Nodulation

Soichiro Tsutsumi, Naoya Kawamura, Kei Horita, Hiroma Mori, Yuki Ishii (Fukuoka Prefectural Denshukan High School, Japan)

With the global increase in food demand, the use of nitrogen fertilizers in agriculture has expanded rapidly. However, excessive nitrogen application causes environmental problems such as nitrate leaching and emissions of nitrous oxide (N₂O), a greenhouse gas. Therefore, sustainable nitrogen management that reduces dependence on chemical fertilizers while maintaining crop productivity is increasingly important. Soybean, a leguminous crop, can utilize atmospheric nitrogen through symbiosis with rhizobia. Previous studies have shown that excessive external nitrogen, especially nitrate nitrogen, suppresses nodulation and nitrogen fixation activity. In contrast, low concentrations of ammonium nitrogen may allow both plant growth and nodulation to occur simultaneously. The purpose of this study is to clarify how different forms of inorganic nitrogen affect the symbiotic relationship between soybean and rhizobia as well as plant growth. Soybeans will be cultivated under combinations of rhizobium inoculation and several nitrogen conditions: nitrogen-free, ammonium nitrogen, nitrate nitrogen, and urea treatments. Plant height, leaf number, leaf color, nodule number, nodule weight, and biomass will be measured to compare growth responses among treatments. Particular attention will be paid to the extent to which external nitrogen suppresses nodulation and whether low concentrations of ammonium nitrogen can support both nodulation and plant growth. In addition, the relationship between plant biomass and nitrogen input will be analyzed to evaluate the potential contribution of rhizobium symbiosis to improved nitrogen use efficiency. This study aims to provide fundamental knowledge for sustainable nitrogen management and to explore the potential of low-input agriculture utilizing rhizobium symbiosis.

Message to the Kyoto Declaration process:
For future generations, society must shift from simply “controlling nitrogen” to “coexisting sustainably with nitrogen.” Through advances in science and technology, together with greater public awareness, we can build a future where environmental protection and food production are balanced in harmony.