Urease inhibitors found in protected urea have no significant effect on fungal and bacterial communities, according to a new study by Teagasc.
The conducted study demonstrated that there was no impact of the urease inhibitor N-(n-butyl)thiophosphoric triamide (NBPT) on the structure and abundance of soil bacterial and fungal communities.
The inhibitor, which is incorporated into protected-urea fertiliser, was repeatedly applied to an intensively managed grassland for five years as part of the study.
Microbial communities involved in nitrogen cycling and nutrient-transformation processes remained unchanged with the use of the urease inhibitor, according to the study published in the scientific journal ‘Soil Biology and Biochemistry’.
Fertiliser, either calcium ammonium nitrate (CAN) or urea, did change the fungal community structure, while bacterial communities were unaffected by either, Teagasc soil microbiologist, Aoife Duff said.
Urease inhibitors such as NBPT, Teagasc said, block the active site of the urease enzyme thus moderating the speed of urea conversion to ammonium in or on soil.
This results in reduced nitrogen losses and greater nitrogen-use efficiency. According to previous research from Teagasc:
“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, which is a potent greenhouse gas, has much higher global-warming potential than carbon dioxide, which is also damaging to the ozone layer, according to Teagasc.
In Ireland, agriculture accounts for 92.2% of nitrous oxide and virtually all ammonia emissions, which, Teagasc said, can lead to eutrophication and acid depositions harming biodiversity and ecosystem health.
While the use of protected-urea fertiliser is currently being employed to mitigate these emissions, the impact on the underlying soil biology needs to be assessed to implement inhibitor technologies at farm level.
Considering the biological health of soil, farmers are advised to maximise on-farm sources of nutrients being returned to soil, Teagasc soil microbiology researcher Fiona Brennan said.
The researcher explained that, 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”.
Where inorganic nitrogen fertilisers are being applied to meet plant-growth requirements, protected urea is a good option for reducing nitrogen losses, Brennan said.