Fine Particle Urea and Urease Inhibitors: What the Trial Found

Fine particle urea outperforms granular urea on nitrogen use and leaching, and adding a urease inhibitor cuts most of the ammonia and nitrous oxide loss on top of that.

Based on the peer-reviewed paper “Urease inhibitor reduces N losses and improves plant-bioavailability of urea applied in fine particle and granular forms under field conditions” by K. Dawar, M. Zaman, J. S. Rowarth, J. Blennerhassett and M. H. Turnbull, Agriculture, Ecosystems and Environment (2011). Run by the University of Canterbury and Massey University, with Ballance Agri-Nutrients as a co-author and funder.

How the trial was set up:

• Urea applied two ways: conventional granular, and fine particle application (FPA), a fluid made from finely ground fertiliser mixed with water and sprayed on.
• Both forms tested with and without the urease inhibitor NBPT (sold as Agrotain).
• Applied at a single rate of 100 kg of nitrogen per hectare, on grazed pasture near Lincoln, Canterbury.
• Measured using lysimeters and field plots over 63 days.
• Ammonia and nitrous oxide losses to air, nitrate leaching, and pasture dry matter were all measured.
• This tested a spray application method and rate under research conditions, not Tow and Fert equipment.

What they found:

• Fine particle urea alone lifted nitrogen response efficiency from 10 to 19 kg of dry matter per kg of nitrogen applied, and increased pasture dry matter by 27% over granular urea.
• Fine particle urea alone also cut nitrate leaching, from 2.1% of applied nitrogen down to 0.92%.
• Fine particle urea alone made little difference to ammonia loss.
• Adding NBPT made the biggest difference to ammonia loss, cutting it by 65 to 69% in both granular and fine particle form, and reduced nitrous oxide loss by 7 to 12%.
• Fine particle urea with NBPT together gave the best result on every measure: nitrogen response efficiency rose to 23 kg DM/kg N, dry matter rose 38% over granular urea, and nitrate leaching fell to 0.05% of applied nitrogen.

The researchers’ conclusion: application method and the urease inhibitor each mattered, but for different losses. Fine particle application did most of the work on leaching, and the inhibitor did most of the work on ammonia. The two together gave the strongest result overall.

👉 Download the full research PDF below to explore the trial data, charts and detailed results.