Nitrification inhibitors: performance drivers

Nitrification inhibitors: performance drivers

SoilBackground

Nitrification inhibitors show great potential to reduce nitrous oxide emissions, but their effectiveness is not consistent across different soils, crops and climates. Information on the efficacy and the ability of the inhibitors to decrease nitrous oxide production under Australian conditions is also very limited.

The interactions of inhibitors with other soil nitrogen pathways are complex, and a more complete understanding is necessary before CFI methodologies can be established.

This project expanded on the earlier enhanced efficiency fertiliser study by quantifying reductions in nitrous oxide emissions from the use of nitrogen fertilisers amended with nitrification inhibitors.

Project outline

Four nitrification inhibitors - 3,4-dimethylpyrazole phosphate (DMPP), dicyandiamide (DCD), N-serve and 3MP+TZ - were tested in different soils under a variety of climates relevant to the major Australian agricultural crops.

Tracer techniqueswere used to distinguish nitrous oxide sources, pathways of nitrogen losses and nitrous oxide / nitrogen gas ratios in denitrfication. Molecular techniques will examine key soil microbial mechanisms associated with using inhibitors to explain why they are not always effective.

Researchers aimed to determine why inhibitors work well in some soils and not others by examining key soil microbial mechanisms associated with the nitrification process. Algorithms simulating the impact of inhibitors on nitrous oxide emissions were developed for different farming scenarios, and verified using field trials conducted by collaborators.

Laboratory experiments were conducted using 30 soils. Field experiments enabled a direct comparison with other fertiliser application methodologies being investigated. This was important for understanding the nitrogen-rate response with nitrification inhibitors.

Information from laboratory and field experiments and from the NANORP collaborative projects enabled robust testing of algorithms describing nitrification inhibitor behaviour under different soil-climate conditions.

Results to date

Across the laboratory studies, nitrifi cation rates were reduced on average by 39% and nitrous oxide emissions by 60%. Some soils showed up to 100% reduction for both measures. Higher soil pH and organic carbon both slightly reduced inhibitor efficacy. 

The inhibitors were most effective at reducing nitrous oxide emissions in the vegetable soils, followed by the cropping and sugarcane soils. They were least effective in the pasture soils. The effect of the soil microbial community on inhibitors efficacy is likely to be signifi cant, and requires further investigation.

In the field studies, the nitrification inhibitor-amended fertiliser (urea with ENTEC®) reduced nitrous oxide emissions (dairy: 47%, cropping: 52%) but had no effect on plant productivity. Recovery of fertiliser nitrogen from the topsoil was higher under the inhibitor treatment but there was no difference in plant recovery of applied nitrogen, supporting the observation that inhibitor use did not improve plant productivity.

The project’s findings indicate that nitrification inhibitors have potential for use as an emissions reduction methodology for Australian producers, however the lack of guaranteed productivity benefits from inhibitors use may limit adoption of the products by industry.

Outcomes

The project’s findings provide further verification of PICCC’s other nitrous oxide work, with the inhibitors tested effective at reducing nitrous oxide emissions across a variety of soils and climates.

The research can provide data for the development of an emissions reduction methodology, however without proven productivity benefits, inhibitor-amended fertilisers may remain financially unviable for most Australian production systems.

Related resources

Titlesort ascending Excerpt
Nitrous oxide publications A bibliographic survey of research publications produced by PICCC's nitrous oxide projects.
Nitrous oxide and fertilisers fact sheet Fact sheet profiling PICCC's two projects on enhanced efficiency fertilisers for nitrous oxide mitigation.
N2O Network The website of the National Agricultural Nitrous Oxide Research Program (NANORP).
Enhanced Efficiency Fertilisers webpage The webpage of the Enhanced Efficiency Fertilisers research group at the Faculty of Veterinary and Agricultural Sciences.