Back to search

BIONÆR-Bionæringsprogram

New generation biofertilizers for improved nitrogen management, sustainable food production and low greenhouse gas emissions

Alternative title: Ny generasjon organisk gjødsel for bedre nitrogenutnyttelse, bærekraftig matproduksjon og lave utslipp av klimagass

Awarded: NOK 5.0 mill.

Biotechnology for reduced N2O emissions from farmland The project has searched along two tracks for reducing N2O emissions. One is to use nitrification inhibitors (NI), compounds which selectively inhibit ammonium oxidation in soil. The second is to grow N2O-reducing bacteria in the waste from biogas production (digestates) prior to fertilization of soils with the digestates. Nitrification inhibitors (N): together with Chinese colleagues, we have confirmed what others have found, that NI can reduce the N2O emission from soils, but we have explored the mechanisms in more detail. We find that the effect of DMPP (3,4-Dimethylpyrazone, a promising NI) increases with increasing soil pH, which is due to a selective inhibition of ammonia oxidizing bacteria (AOB), but not ammonium oxidizing archaea (AOA): the abundance of AOB is increasing with increasing soil pH. When analyzed with such a model (selective inhibition of AOB), we find that the concentration of DMPP that reduced AOB-activity with 50% is very similar for all soils (0.3-0.6 mg DMPP pr L). It is well known that AOB produce more N2O than AOA, and our measurements of N2O production at different DMPP-concentrations corroborate this: the N2O/NO3 product ratio drops with increasing DMPP concentrations. DMPP qualifies as an probate substance for reducing the N2O emission from nitrification, albeit with a modest effect (< 10% reduction of the annual emissions). Large scale DMPP application could be controversial, however. One would expect emergence of legitimate reluctance to poisoning our soils. The second track is more promising; bacteria that are strong sinks for N2O are called NRB (N2O-reducing Bacteria). NRB can be strong sinks because they their expression of the enzyme which reduce N2O (NosZ) is stronger than their expression of the enzymes which produce N2O (Nar, Nir, Nor). But a stronger version of NRB’s are those which lack the genes coding for Nar and Nir, because the cannot produce N2O. To find and isolate effective NRB, we have used enrichment culturing, monitored by several molecular techniques to unravel which organisms that are growing, and which denitrification genes they have, and which of these genes that are transcribed. We were able to isolate several NRB’s, but inspection of their metabolic and respiratory potential revealed that they were far from ideal: 1) their catabolism was streamlined for growing in a live digestate (thus exploiting a narrow suite of monomers produced by other organisms), thus unable to survive in soil. 2) all of them had a full- fledged denitrification pathway, thus able to both produce and reduce N2O. Based on these results, we refined the enrichment culturing, deliberately searching for NRB with a broader catabolic potential. This resulted in a breakthrough: we have found NRB which 1) lacks the genes coding for Nar and Nap, thus being net sinks for N2O under all circumstances 2) grow fast in digestates 3) exploit a broad specter of C sources and survives for longer time in soil than previously isolated NRB’s. Subsequent enrichments, using a variety of organic wastes as substrate has resulted in the isolation of a suite of new NRB’s that are not yet fully investigated. We have now tested the effects of the NRB-technology in field scale experiment, and have found the NRB reduces the N2O emission from farmland with 50-95% depending on the soil type. Further, we find that our NRB’s can grow in straw, which opens for application of the technology for farms without access to digestates. A new project was initiated in 2022, which will follow up the development of the technology, and a spinoff company will be established to promote the technology both nationally and internationally.

Teknologien vi har utviklet vil med enkle grep redusere emisjon av lystgass fra landbruksjord, og dermed redusere klimapådrivet fra matproduksjon. Vi forventer at den vil tas i bruk, og vi vil drive dette frem ved å ta teknologien til et høyere TRL-nivå, og etablere et selskap som skal promovere dette nasjonalt og internasjonalt. Vi forventer hindringer: på tross av at kostnadene forventes å være moderate må de dekkes på en eller annen måte. I og med at landbruket ikke kan selge reduserte utslipp på GHG kvotemarkedet må det søkas andre policy instrumenter.

Anaerobic digestion (AD) will become the standard way of treating sewage sludge, urban organic wastes and animal manure, both in Norway and China, and the digestates are increasingly used to fertilize farmland. One important motivation for these huge investments in AD-technology is to reduce climate forcing by eliminating methane emission from storage and to replace fossil fuel with biogas. Here we propose to add a new dimension to the climate performance of AD: by growing aggressively N2O reducing bacteria (ANB) in the digestates, we can reduce the N2O emission which is otherwise induced by the fertilization with the digestate. We will search for biodigestate-competent ANB that also grow/survive in soil, thus securing a more long lasting reduction of the N2O emission from farmland. Finally, we will explore if retardation of nitrification by modest doses of nitrification inhibitors can reduce the aerobic N2O emission caused by ammonia oxidation. We have recently identified several types of bacteria that can potentially act as strong N2O sinks, either because their only denitrification gene is the one coding for N2O reductase (nosZ), or because they express nosZ more than the other denitrification genes. A primary challenge will be to enrich such organisms in the digestates. We will use either digestates or soils as initial inoculum and select for ANB by providing a suitable electron acceptor. Metagenomics and proteomics will be used to track and identify the dominating organisms in the enrichment, and to guide attempts to isolate ANBs. Microcosms will be used to test the effects of ANB on N2O kinetics in soils, and to test the effects of nitrification inhibitors. Upscaling to field experiments will be done by cultivation in pilot plants, and possible implementations in existing AD systems will be explored in collaboration with AD industries that are associated with the project.

Publications from Cristin

No publications found

No publications found

No publications found

Funding scheme:

BIONÆR-Bionæringsprogram