Utilization of Biological Nitrification Inhibition (BNI) function for the development of breeding materials and application to cropping systems
Nitrification, a key process in the global nitrogen cycle that generates nitrate through microbial activity, enhances losses of fertilizer nitrogen by leaching and denitrification. The rapid and unrestricted nitrification found in most intensive production systems results in the N loss of up to 60% of N-fertilizer inputs, amounting to a direct economic loss of US$ 81 billion annually. Agricultural systems contribute up to 70% of the global N2O emissions, a powerful greenhouse gas with a global warming potential 300 times that of CO2. Nitrification and denitrification are the only known biological processes that generate N2O emissions. Fertilizer N use is expected to reach 300 Tg y-1 by 2050 and this will further intensify the N losses to the environment. Current estimations suggest that N losses from NO3- leaching will reach 61.5 Tg N y-1 and from N2O emissions will reach 68 Tg N y-1 by 2050. Regulating nitrification thus is central to any mitigation strategy to reduce N2O emissions from agricultural systems and to combat global warming. Biological nitrification inhibition (BNI) is an active plant-mediated natural function, where nitrification inhibitors released from plant roots suppress soil-nitrifying activity, thereby forcing N into other pathways to minimize N losses from agricultural systems. (Fig. 1). Our ongoing research suggests that such BNI capacity is widespread among plants, with Brachiaria pasture grasses showing the highest capacity among the pasture grasses tested. Field tests have confirmed that Brachiaria humidicola can suppress N2O emissions and reduce soil nitrification potential. Among field crops evaluated, sorghum showed significant BNI capacity in its root systems. Also, nitrification inhibitors were isolated from the root exudates of B. humidicola and sorghum and their chemical identities were established.
The current BNI project is aimed at:
- Clarifying the BNI function which includes isolation of BNI activity, develop in-depth knowledge on regulatory mechanisms associated with their release and conditions for optimum expression in sorghum.
- Develop genetic tools that include genetic contrasts for BNI capacity and genetic markers associated with BNI-capacity in sorghum and Brachiaria sp. as model systems.
- Develop cropping systems-based approaches to exploit the BNI function in order to reduce soil nitrification potential and to improve the nitrogen economy in agriculture systems.
The long-term goal of this research is to develop low-nitrifying and low N2O- emitting crops using a combination of genetic and agronomic strategies to develop sustainable agricultural systems that are productive, but least damaging to the environment.