Dairy farmers can improve production efficiency and reduce environmental impact by improving NfUE.
Improving the economics and resilience of home-grown forage production is a challenge now faced by all dairy producers but there’s a lot that dairy farmers can do to improve production efficiency and reduce their impact on the environment says independent grassland specialist Dr. George Fisher.
“Talk to any dairy farmer and they’ll tell you their number one objective is improving profitability and fortunately, research is showing that reducing issues such as N loss to the atmosphere will also have a significant impact on overall business profitability. Much of this revolves around how different types of fertiliser work once they hit the ground, how much of the available N is taken up by the plant and how much is either lost to the atmosphere or left in the ground, where it is vulnerable to further losses, he says.
NUE AND NfUE efficiency
Nitrogen Utilisation Efficiency (NUE) takes into account all sources of N, be they from the soil or applied organic manures and it is an obviously important benchmark, but singling out the performance of bought-in fertiliser can often be more informative from a practical management perspective. The calculation involves a simple equation where the Nitrogen removed from grassland with no fertiliser applied, is subtracted from the amount of N removed when the optimum level of bought-in fertiliser is applied. If you then divide this figure by the level of N applied that gives you an indication of the Nitrogen Fertiliser Use Efficiency (NfUE) which is expressed as a percentage.
The higher this value, the more N your silage or grazing is taking up and the less there is that is being lost from the system – you then have a valuable indicator of fertiliser use efficiency to make direct comparisons between fertiliser N sources.
Fertiliser product choice and NfUE
Three years of CF trials have given a valuable insight into how and why NfUE differs in different systems. The trials revealed a wide variation in values from different sites and fertiliser types with NfUE values ranging from 50% to 85% but one constant in evidence is that high quality Ammonium Nitrate (AN) consistently outperforms urea and when you start managing other nutrients such as P, K and S effectively, the advantage grows.
- Using Nitram (34.5% N) produced a lift of about 10% points in NfUE over urea regardless of yield differences (across 5 trials on 5 different sites).
- In grazing, Nitram had a 83% NfUE compared to 73% for urea
- In silage Nitram had a 70% compared to 59% for urea
This is down to two things.
- You lose less N to the air when you use AN
- AN treated grass has a higher N content than urea treated grass
Overall this is a reduction in N loss to the atmosphere of around 20% (in kg N/ha) from using Nitram compared to urea in grassland so if you’re using 240kgN/ha for your silage land, around 50kg/ha N more will be retained within the production system with Nitram compared to urea.”
“There is a perception that N from urea leaches in to water less than from AN but this is not a given. Leaching losses are much smaller than volatilisation losses from urea, and they happen in the autumn and winter when soils wet-up and drain. By this time, the AN and urea fertilisers have both been converted to nitrate, which is the main leached form of N.” says George Fisher.
The effect of Sulphur on NfUE
If you then add in the potential extra efficiencies from using Sulphur in your fertiliser, the gains are even greater as Sulphur can have a profound effect on the ability of grassland to utilise N and hence inadequate levels can really drive NfUE % down.
Where Sulphur is needed, adding S to AN increases N efficiency by a further 10% due mainly to increased grass yield.
In grazing trials, where the N and S was applied as CF SingleTop (27N 12 SO3) a NfUE of 84% was recorded compared to 74% for straight AN, and in silage this was 79% and 65% respectively, he points out.
By applying the combined NS product containing Nitrogen and Sulphur, N efficiency is increased by 10% and this is in addition to the 10% improvement from AN over urea.
“So the difference in NfUE between using SingleTop as opposed to straight urea is 20% which equates to a 40% reduction in N loss to the environment.
The question is, can you get the same efficiency and cost benefits from adding Sulphur to a urea fertiliser N base, as you get from Sulphur with an AN fertiliser base?
“The answer is no. Volatilisation from urea happens whether or not it’s combined with Sulphur.”