Urea vs. AN – what is cost effective this year?

Published 13 March 15

Fertiliser prices for February 2105 were back slightly on 2014, with urea and ammonium nitrate (AN) averaging £290 per tonne. However, it is still a good time to look at the differences between the two, and evaluate which is the most cost-effective to use and when. AHDB Dairy Research and Development manager, Dr Debbie McConnell, takes a look at how to make the most out of them this year.

This year’s February prices have fallen about 5p per kg of nitrogen but urea remains over 20% cheaper than AN per kg of nitrogen (N). To take advantage of this cheaper form of N, it is important to make the most of the spreading conditions.

Urea

Urea is most effective in low temperatures and when rainfall is present in the three days following treatment, making spring time applications particularly effective.

Rainfall will ensure the urea will be washed into the soil, where nitrifying bacteria convert it to ammonium-N and the ammonium-N to nitrate, which is then available for uptake by the plant. However, at higher temperatures and at low levels of rainfall, large amounts of ammonia gas will be lost to the atmosphere, as a result, grass growth response to urea will be below that of AN. In optimum conditions, the response to urea can significantly outperform AN (+33%; see Table 1). However, if used in sub-optimal conditions response can be reduced by as much as 32%. 

Urea v AN table

But what level of grass growth response is required to make it cost-effective to use urea over AN? Looking at February 2015 fertiliser prices (Urea = 0.63p/kg N, AN = 0.83p/kg N), above a relative response of 76% of urea compared to AN, it will be more cost effective to spread urea than AN. Therefore, it is only in dry conditions and at temperatures above 12.5oC that it is cost effective to spread AN (Figure 1, green area).

Figure 1: Relative response of grass growth to application of urea N compared to AN, depending on rainfall and temperature conditions. Below a urea grass growth response of 76% (relative to AN), it is more cost effective to spread AN (green area; Urea = £290/t, AN = £290).

Urea v AN graph 1


If, however, AN prices remain static and the price of urea rises £40 per tonne, the relative grass growth response above which it becomes cost effective to spread urea rises to 87%. As a result, urea should only be spread when some rainfall is forecast and at lower temperatures (Figure 2, white area). If urea falls to £250 per tonne, and AN remains at £290, it is not cost effective to spread ammonium nitrate until temperatures exceed 20
oC.

Figure 2: Relative response of grass growth to application of urea N compared to AN, depending on rainfall and temperature conditions. Below a urea grass growth response of 87% (relative to AN), it is more cost effective to spread AN (green area, urea = £330/t, AN = £290).

 Urea v AN graph 2

Summary

  • Current fertiliser prices indicate that cost savings can be made by using urea over ammonium nitrate (AN), however, urea must be used in optimum conditions to make the most of this price differential.
  • Urea is most effective in spring in low temperature conditions when rainfall is present
  • At current fertiliser prices (February 2015) above a growth response to urea relative to AN of 76% it is more cost effective to spread urea.

 For up-to-date information on fertiliser prices visit the Market Information page on the website.