Low-temperature plasma converts air to ammonia using electricity, advancing beyond Haber-Bosch

Researchers at Nagoya University and Kyushu University have published a comprehensive review of plasma agriculture, a field that uses controlled electrical discharges to convert atmospheric nitrogen into ammonia, nitrites, and nitrates in plasma-activated water — without the high-temperature, high-pressure conditions and fossil fuel inputs that define the dominant Haber-Bosch process.

The review, authored by Pankaj Attri, Kenji Ishikawa, and Kazunori Koga of Nagoya University’s Center for Low-temperature Plasma Sciences, was published in the Journal of Advanced Research on July 15. It synthesizes data from more than 30 crop species across hundreds of reported studies.

What low-temperature plasma agriculture nitrogen fixation does

Conventional nitrogen fertilizer production relies overwhelmingly on the Haber-Bosch process, which combines atmospheric nitrogen and hydrogen at high temperature and pressure in the presence of an iron catalyst to produce ammonia. Natural gas provides both the feedstock hydrogen and most of the process energy. This dependence ties nitrogen fertilizer costs closely to natural gas prices, creating the kind of supply and cost volatility that characterized the 2022 European gas crisis and the 2026 Hormuz-related fertilizer price spike.

Low-temperature plasma offers a different pathway. When an electrical discharge passes through air, it breaks the exceptionally stable triple bond in nitrogen molecules, creating reactive nitrogen species — including ammonia, nitrites, and nitrates — in the surrounding medium. Applied to water, this process produces plasma-activated water: a liquid solution carrying plant-usable nitrogen compounds at concentrations relevant for crop nutrition.

Beyond nitrogen fixation, plasma treatment affects plant biology directly. The reactive oxygen and nitrogen species generated in plasma-activated water or by direct plasma exposure interact with seed surfaces and plant tissues in ways that alter germination rates, root development, and stress responses. The review by Attri, Ishikawa, and Koga compiles the mechanistic and agronomic literature on these effects.

Results across crop species

In more than two-thirds of the studies reviewed, tuned plasma treatments boosted seed vigor or final yield across the crop species examined. The 30-plus species include cereals such as wheat, corn, and rice; legumes; and specialty crops. The remaining studies reported neutral effects or reductions in yield, typically attributable to plasma doses that were not properly calibrated for the species or growth conditions involved.

Professor Kenji Ishikawa described the technology’s positioning to Nagoya University media, characterizing low-temperature plasma as an alternative to genetically modified crops for enhancing resilience and yield. Unlike genetic modification, which requires regulatory approval and carries market acceptance challenges, plasma treatment is a physical process applied externally.

The review also documents plasma’s capacity to trigger systemic effects in plants that go beyond seed treatment, including altered root growth and enhanced uptake efficiency of soil nutrients.

Path to field deployment

The review is explicit that the transition from laboratory-scale plasma systems to farm-level deployment requires deeper understanding of the physical and biochemical mechanisms through which plasma acts. Three barriers stand out in the literature surveyed.

First, plasma dosing is highly sensitive to species, growth stage, and application timing. The dose-response relationship is non-linear: treatments that stimulate germination at one exposure level can inhibit growth or damage seed tissue at higher levels. Field conditions — variability in moisture, temperature, seed lot quality, and equipment — make dose reproducibility far more difficult than in controlled greenhouse environments.

Second, the nitrogen concentrations achievable in plasma-activated water at current energy efficiencies remain substantially below those delivered by conventional nitrogen fertilizers per unit application. Scaling up plasma-activated water nitrogen to volumes relevant for large-scale crop production would require significant advances in electrolyzer design and plasma reactor efficiency.

Third, while the fundamental physics of plasma nitrogen fixation has been studied since the early twentieth century, the biological pathways through which plasma-reactive species interact with plant cells, soil microbiota, and the rhizosphere are not yet fully characterized. The review identifies this mechanistic gap as a priority for future research.

Relevance for the fertilizer industry

Plasma agriculture is not a near-term commercial substitute for synthesized nitrogen fertilizers at the scale of global crop production. The researchers themselves position their review as a map of the current state of knowledge rather than a demonstration of commercial readiness.

The technology is, however, well-suited to two near-term applications where it could develop more rapidly: high-value horticulture, where energy and equipment costs are easier to absorb per unit of product, and distributed or off-grid farming contexts, where the ability to fix nitrogen using renewable electricity without centralized ammonia infrastructure represents a logistical advantage.

The Nagoya review arrives at a moment when sustained high nitrogen fertilizer prices, Middle East supply disruptions, and European decarbonization mandates are accelerating interest in alternatives to fossil-fuel-dependent nitrogen production. Plasma agriculture, alongside biological nitrogen fixation approaches using engineered bacteria and CRISPR-modified crops, is one element of a broader portfolio of technologies aiming to reduce that dependence.

Source: Phys.org / Nagoya University