Unlocking bacterial potential to reduce farmland greenhouse gas emissions

Farmed soils contribute significantly to global warming by emitting nitrous oxide (N₂O) alongside other greenhouse gases. Mitigating field-based N₂O emissions, originating from soil upon fertilizer or manure application, is particularly challenging. This is primarily because these emissions vary greatly in space and time, depending on soil type, weather, fertilizer management, and agronomic management practices.

In this new study, researchers used a bioaugmentation approach, employing the N₂O-respiring bacterium Cloacibacterium sp. CB-01 to reduce N₂O in the soil. Bacterial metabolization resulted in the emission of harmless N₂ gas.

Fertilization with biodigestate (a waste product from biogas production), in which Cloacibacterium had been grown, reduced N₂O emissions by 50–95%, depending on soil type. This is an impressive achievement, but also merely a proof of concept.

What the authors describe as ‘field experiments’ were, in fact, experiments in small soil buckets and one experiment in field microplots of 0.5 m² size. In the latter, they applied the bacteria-cultured digestate at a rate of 9 l per m², or 90,000 l per hectare. For most practical purposes, this is an unrealistically high application rate, likely overstating the outcomes that may be achieved in reality.

Unfortunately, despite this limited field evaluation, the authors proceeded to scale up their findings by using a model for the whole of Europe. They state, “…we find that national anthropogenic N₂O emissions could be reduced by 5–20% and more, if including other organic wastes.” Such speculation should have no place in science until much more field evaluation has been conducted using substrates (e.g., manure), at application rates and under management conditions that are representative of farming.

Although bioaugmentation may play an increasing role in managing nutrient cycles in farmed soils, rigorous evaluation of such interventions is needed. This includes comparisons with other technologies that have proven modes of action, such as chemical nitrogen inhibitors.