While urea is the cheapest option per kg of N, it can suffer from losses in the field due to ammonia volatilisation.
Stabilised urea, also known as treated or protected urea, containing additives such as NBPT, has been shown to reduce ammonia volatilisation losses compared to urea by 78.5% on average, whilst maintaining comparable yields to Calcium Ammonium Nitrate (CAN), (AFBI & Teagasc research 2017).
Whilst losses of ammonia from CAN are lower than urea, CAN is vulnerable to loss of nitrogen by one of the most potent greenhouse gases - nitrous oxide (N2O), and in wet years by nitrate leaching. For spring dressings stabilised urea will release much less ammonia than straight urea, have significantly lower N2O emissions than CAN, yet produce reliable yields.
Remember it is essential to change the settings on your fertiliser spreader when switching between products to achieve an appropriate bout width to maximise fertiliser efficiency. Urea is less dense and prill size is 3-5mm, compared to CAN at 5-7mm. Check that discs and vanes are free of mud and in good condition.
A tray calibration test can confirm the evenness of fertiliser spread and allow for adjustments.