Biological nitrification inhibitors

Biological nitrification inhibitors (BNIs) are compounds released by plant roots that suppress the soil bacteria and archaea converting ammonium (NH4+) into leachable nitrate (NO3-) and nitrous oxide. Less than 50% of applied fertilizer nitrogen is taken up by crops; the rest is lost to nitrification, denitrification and volatilisation. A spatially explicit 2026 assessment found that BNI-enabled maize could cut global fertilizer demand by 1.4–3.9% and fertilizer-related greenhouse-gas emissions by 11.2–18.2%. The best-characterised BNI compounds — the cyclic diterpene brachialactone from the tropical grass Brachiaria, benzoxazinoids (DIBOA, DIMBOA, BOA, MBOA) from wheat and maize, and the newly isolated coracanols from finger millet — each inhibit Nitrosomonas and Nitrosospira at low concentration. BNI wheat lines carrying a chromosome fragment from the wild grass Leymus racemosus inhibit nitrification up to two-fold more than their parent lines, and modelling suggests BNI crops could reduce nitrogen losses by 20–30% with no yield penalty. Unlike synthetic inhibitors (nitrapyrin, DCD, DMPP), BNIs are produced in the rhizosphere by the crop itself.

The key directions of biological nitrification inhibition are:

1. Brachialactone and cyclic diterpenes (Brachialactone & Cyclic Diterpenes): BNI compounds from Brachiaria and finger millet (coracanols A and B), discovered and characterised by JIRCAS.
2. Benzoxazinoid BNIs in cereals (Benzoxazinoid BNIs): DIBOA, DIMBOA, BOA and MBOA from wheat, maize and rye that suppress Nitrosomonas at low concentration.
3. Triterpenoid and phenylpropanoid BNIs (Triterpenoid & Phenylpropanoid BNIs): boswellic acid, ursolic acid and sakuranetin identified by high-throughput screening as inhibitors of ammonia-oxidizing archaea.
4. BNI trait breeding (BNI Trait Breeding): introgression of BNI-active chromosome fragments into elite wheat and maize, scaling BNI from a plant trait into commercial cultivars.

Sectoral value chain#

[BNI compound discovery] ──> [trait mapping] ──> [breeding] ──> [field evaluation]
                                   │
                           (suppress Nitrosomonas)
                                   │
                                   ▼
[deployment] <─── [registration] <─────┘

Value chain levels#

Cross-cutting technologies of the sector:

• Hydroponic BNI bioassay (Hydroponic BNI Bioassay): standardized recombinant Nitrosomonas assay to quantify BNI activity across genotypes.
• Root-exudate metabolomics (Root-Exudate Metabolomics): combined GC/LC-MS profiling and graph-neural-network models linking metabolites to BNI activity.
• Marker-assisted BNI introgression (Marker-Assisted BNI Introgression): moving BNI chromosome fragments from wild relatives into elite wheat and maize.

The stack combines high-throughput BNI bioassays, root-exudate metabolomics and marker-assisted breeding to turn a plant trait into deployable cultivars.

1. Hydroponic BNI bioassay (Hydroponic BNI Bioassay):
   • a standardized recombinant Nitrosomonas europaea assay quantifies BNI activity across germplasm in weeks rather than field seasons.
   • extension to ammonia-oxidizing bacteria (AOB) and archaea (AOA) separates the two nitrifier domains synthetic inhibitors often miss.
2. Root-exudate metabolomics (Root-Exudate Metabolomics):
   • combined GC- and LC-MS platforms profile thousands of metabolic features in root exudates of diverse genotypes.
   • graph-neural-network and machine-learning models identify the combinations of metabolites (not single compounds) that drive rhizosphere BNI activity.
3. Marker-assisted BNI breeding (Marker-Assisted BNI Breeding):
   • BNI chromosome fragments from wild relatives such as Leymus racemosus are introgressed into elite wheat, doubling nitrification inhibition with no observed yield penalty.
   • CIMMYT’s CropSustaiN program scales the pipeline toward BNI-enabled maize and wheat for low-input systems.