NZ Emissions Reduction: Lincoln University Breakthrough On Nitrification Inhibitors
October 14th, 2009
Lincoln University scientists have discovered more precisely how nitrification inhibitors work in the soil, leading to a potential breakthrough in reducing nitrous oxide emissions to the atmosphere. Nitrification inhibitors slow down the conversion of ammonium in the soil to nitrate. The ammonium comes from animal urine and nitrogen fertiliser applied to pasture. Once ammonium becomes nitrate, the soil holds the nitrate less securely, and it can leach into waterways or be converted to the greenhouse gas nitrous oxide, which contributes to global warming and is 16% of NZ’s GHG emissions. Unlike methane, which accounts for 34% of total NZ emissions, there are already commercially applicable circumstances for farmers to use nitrification inhibitors and reduce emissions.
Lincoln scientists, lead by Professor Hong Di and Professor Keith Cameron, have discovered that the nitrate and nitrous oxide reductions achieved by the commonly sold product dicyandiamide (DCD) are largely due to its inhibiting effect on ammonia-oxidising bacteria. Till now it had been assumed simple, single-celled organisms called archaea (similar but separate to bacteria) were the main oxidising agents in rich grassland. The Foundation for Research, Science and Technology funded study is a collaboration with the Chinese Academy of Sciences and AgResearch to improve dairy farming environmental sustainability. The research aims to reduce nitrate leaching into groundwater and nitrous oxide into the atmosphere from cow urine and nitrogen-based fertiliser use.
Indications are archaea may be specially adapted to more unfavourable conditions such as low fertility. Bacteria appear to thrive in high fertility soils, especially flourishing where soils receive fertiliser nitrogen boosted by animal urine. Ammonia oxidising archaea are present in large numbers from six soil samples taken from around NZ, and these are assumed to play an important part in breaking down ammonia.
But Professors Di and Cameron say “neither their abundance nor their activity increased with the application of an ammonia substrate such as urine. In contrast the number and activity of ammonia oxidising bacteria increased many fold in response to the addition of ammonia. The implication is that we should focus on bacteria in the development of mitigation technologies.”
The breakthrough discovery has just been published in the prestigious international science publication Nature Geoscience (2:621-624, 2009).
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