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New Teagasc study finds no impact of inhibitors on the soil microbiome


New research from Teagasc Johnstown Castle has demonstrated that there was no impact of urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), incorporated into protected urea fertiliser, on the structure and abundance of soil bacterial and fungal communities after 5 years repeated application

The research results followed five years of repeated application to an intensively managed grassland.

The study, which has been published in the scientific journal, ‘Soil Biology and Biochemistry’, further showed that the microbial communities involved in nitrogen cycling and nutrient transformation processes remained unchanged with the use of the urease inhibitor. Fertiliser application, either via calcium ammonium nitrate (CAN), or Urea did change the fungal community structure, but the bacterial community structure in fertilised plots was not significantly different from the unfertilised plots.

What Urease inhibitors do

Urease inhibitors such as N-(n-butyl) thiophosphoric triamide (NBPT) block the active site of the urease enzyme thus moderating the speed of urea conversion to ammonium in, or, on soil, resulting in reduced nitrogen losses and greater nitrogen use efficiency. Previously, research from Teagasc Johnstown Castle has demonstrated that switching from CAN to protected urea fertiliser reduced nitrous oxide emission factors by 71% and reduced ammonia volatilisation by 78.5%, while maintaining grass yields.

Nitrous oxide & Ammonia emissions

Nitrous oxide is a potent greenhouse gas with a global warming potential much greater than carbon dioxide, which is also damaging to the ozone layer. Ammonia emissions can lead to eutrophication and acid depositions, with negative impacts on biodiversity and ecosystem health. In Ireland, the agriculture sector accounts for 92.2% of nitrous oxide and virtually all ammonia emissions.

The use of protected urea fertiliser is one tool currently being employed to mitigate these emissions, but assessment of the impact on the underlying soil biology is important for implementation of the inhibitor technologies at farm level.

Teagasc research providing solid advice for farmers

Soil Microbiologist with Teagasc, Aoife Duff stated that ‘This study shows that nitrogen fertilisation is a major driver of fungal community change while the urease inhibitors found in protected urea have no significant effect on the fungal and bacterial communities. We also found that the type of fertiliser (CAN or Urea) resulted in differential effects on fungal communities, while bacterial communities were unaffected by either’.

Teagasc Soil Microbiology Researcher, Fiona Brennan said: ‘Our advice from a soil biological health perspective would always be, first and foremost, to maximise on-farm sources of nutrients being returned to soil. For nitrogen, this can be achieved through optimisation of nitrogen fixation via the inclusion of legumes in swards, or cropping systems, and the efficient use of organic manures. Maintaining soil pH and a balanced fertility will also increase nitrogen use efficiency. Where inorganic nitrogen fertilisers are being applied to meet plant growth requirements, protected urea represents a good option for reducing nitrogen losses from the system, which result in a financial loss to the farmer and are potentially damaging to the environment’.

Soil and Plant Nutrition Researcher with Teagasc, Patrick Forrestal stated that “the work highlights the value of long-term field trials where the effects of nutrient strategies on soil health, plant performance and environmental loss mitigation can be evaluated to provide solid advice for farmers and the Agri-Food sector.”

See the published scientific paper at:

 Assessing the long-term impact of urease and nitrification inhibitor use on microbial community composition, diversity and function in grassland soil

Find out more about the Soil Research work at Teagasc environment research centre, Johnstown Castle