Modern agriculture  is faced with the major dilemma of minimizing the environmental damage caused by agriculture while ensuring an adequate food supply. Nitrogen fertilizer is essential for crop growth, and farmers have traditionally increased nitrogen fertilizer inputs to increase food production per unit of land and reduce deforestation caused by the expansion of farmland. At the same time, however, nitrogen fertilizer has become the major cause of greenhouse gas emissions lately and groundwater pollution. Retaining nitrogen in the soil in ammonium form could be the decisive factor in solving the dilemma of increased food production without environmental pollution. The “Opinion” of JIRCAS and Princeton University scientists on these debates was published on June 1 issue (vol. 118 no. 22) of Proceedings of the National Academy of Sciences (PNAS), one of the prestigious journals. JIRCAS and Princeton University had held a press release about this article.

Toward 2050, the world population is expected to increase by 2 billion, mainly in developing countries, to reach about 10 billion. Under the current production system, to avoid deforestation while increasing food production, an increase in the amount of nitrogen fertilizer is inevitable if we try to increase the yield per unit of land, and there are concerns that environmental pollution will worsen. There are ways to minimize pollution by devising ways to apply nitrogen fertilizer, but it is known that nitrogen applied as ammonium-form quickly becomes nitrate in the farmland, easily dissolved in groundwater, and is emitted into the atmosphere as nitrous oxide, 310 times potent greenhouse gases than carbon dioxide.

Research by JIRCAS and partners has shown the potential in some crops which can improve soil ammonium levels by inhibiting nitrifier activity. Ammonium does not convert to nitrous oxide unless it becomes nitrate in the first step. Although large amounts of ammonium are toxic to many crops, mixing nitrate with retained ammonium can achieve crop yield increases of 50% or more over nitrate alone.

However, this method has not been practical until recently due to the "nitrification" in which soil microorganisms rapidly converts ammonium to nitrate. The authors and other collaborators have discovered the ability in some crops to prevent soil microorganisms from nitrifying ammonium to nitrate, which facilitates availability of balanced nitrogen forms for plant uptake. JIRCAS researchers have discovered that such BNI-traits can be enhanced in several staple crops such as wheat to develop wheat varieties with enhanced BNI-capacity in root systems.  By cultivating crops with the ability to inhibit nitrification using ammonium in the soil, it is possible to achieve the dual goals of increasing food production and preventing environmental degradation. Instead of subsidizing fertilizers, the paper appealed for support for the development of fertilizers, chemicals and crops that can reduce nitrification.

The current debate over the global food system encourages technological innovations that enable us to reduce the use of chemical fertilizers and pesticides as much as possible to minimize the environmental impact of food production. JIRCAS has been playing a role in bringing together partners from around the world in the development of biological nitrification inhibition (BNI) as a key mitigation technology, which is expected to contribute greatly to these global issues through the BNI international consortium.

BNI technology is also featured in the Japanese government's “Green Growth Strategy for 2050 Carbon Neutrality” and in the "Green Food System Strategy" released by the Ministry of Agriculture, Forestry and Fisheries in May.

References

JIRCAS Press Release: Ammonium Utilization - A Solution to Nitrogen Pollution and Increased Food Production  https://www.jircas.go.jp/ja/release/2021/press202103 (In Japanese)

G. V. Subbarao, Timothy D. Searchinger  Opinion: A “more ammonium solution” to mitigate nitrogen pollution and boost crop yields. Proceedings of the National Academy of Sciences Jun 2021, 118 (22) e2107576118; DOI: 10.1073/pnas.2107576118

Contributors: SUBBARAO Guntur and YOSHIHASHI Tadashi (Crop, Livestock and Environment Division)