Urea matches the performance of ammonium nitrate (AN) in just over 20% of grassland application scenarios, suggests a study of the last three years’ weather carried out at Reaseheath College in Cheshire.
The work, focused on the years 2015 – 2017, shows that AN produced on average 15% more grass over first and second cut silage compared to urea over the period.
“To get the most economic response to Nitrogen you need to apply it when the crop needs it, not simply when the weather forecast is favourable to urea,” explains CF Fertilisers’ Western Regional Manager James Holloway.
“With urea you need significant rainfall within 3 days of application to wash the fertiliser into the soil where the microbial urease can convert it into nitrate. Without that, losses to air through volatilisation of ammonia make it risky and uneconomic.”
Analysis of weather patterns for the last three years at Reaseheath shows that of the 31 days in March on average there were just 7 where urea would have achieved a similar level of Nitrogen utilisation efficiency as Ammonium Nitrate. (see table 1.)
On some days, the predicted potential yield loss from urea compared to AN was 18% with the average over the days being around and 8% deficit.
For aftercut fertiliser application, it’s even worse with none of the first 15 days of May being suitable for optimum urea utilisation with the resulting average potential loss in grass yield being over 10% and as high as 20% in 4 of the 15 days, when comparing to Nitram Ammonium Nitrate. (see table 2.)
Spreading the weather analysis out over 15 sites from Cornwall to Glasgow for the last five years reveals a similar picture, he adds.
“At 5oC, a not uncommon Spring temperature in the UK, urea needs at least 7mm of rainfall in the three days after application to work effectively, but the analysis shows the chance of getting this is just 25%.
“At 10oC, urea needs at least 10mm rainfall in the three days after application to work and there is then just a 15% chance of this occurring.
“Bottom line is you’re not just losing paid for Nitrogen to the air with urea, you’re potentially losing valuable forage production and increasing your bills from having to buy in feed to replace the lost forage bulk and energy.
“For many producers, using urea simply adds unnecessary risk to a grass-based system.”