There is no doubt events over recent years have forced a change in the way we think about nitrogen, prompting a rethink about how organic manures, ammonium nitrate and urea fertilisers can be used more efficiently, says Tim Kerr, Hutchinsons nutrition manager.
He outlines why: “Firstly, the high cost of N fertiliser has focused attention on maximising the return on a major investment. Secondly, incoming legislation on urea-based fertiliser has highlighted risks associated with the use of urea as a fertiliser, and thirdly, there is a broader recognition that nitrogen fertilisers are the largest contributor to the carbon footprint of crops.”
“To add to this, we have experienced a number of dry springs which have presented challenges in managing nitrogen applications to maintain crop uptake.”
Making better use of Nitrogen
Mr Kerr points out that this is not just about nitrogen fertilisers. “The value of nitrogen in manures has also tripled. An average tonne of poultry manure is now worth more than £50 in available nutrients alone – such a valuable resource should be managed with that in mind.”
Applying manures accurately at the right time and minimising ammonia losses is key. “It’s a win: win – less additional N and a reduction in ammonia emissions and a lower carbon footprint of the growing crop.”
Tim Kerr nutrition manager
“The soil will typically supply around half the nitrogen required as cereals start growing again, but mineralisation of organic nitrogen is temperature and moisture dependant –it is unwise to rely on the soil supplying too much early nitrogen, especially if the soil temperature is below 5 °C at rooting depth,” he says.
“Ammonium nitrate supplies readily available nitrate N as well as slower release ammonium N. Urea once in soil solution will supply ammonium nitrate. For those using urea for the first time – it is worth knowing that urea must undergo chemical change to become plant available.”
On this basis Mr Kerr advises applying it earlier than ammonium nitrate. “Once conditions allow urea can be applied without any major risks attached.”
”The best and most consistent results come from front-loading nitrogen applications. An application of 80kg once conditions allow helps to meet the early crop demand, “he says.
“Once winter cereals begin rapid growth – this will go up to nearly 20kg of nitrogen per week.”
How do you solve a problem like Urea?
Impending restrictions on the use of urea-based fertilisers mean that fertiliser used in the spring of 2024 will need to meet the new guidelines.
Urease inhibitors are effective at reducing the risk of ammonia losses from urea. From 2024 these will need to be used from 1st April each year. However, volatilization cannot be effectively managed by the calendar and if we experience warm dry conditions in March, there could still be significant nitrogen losses from urea.
For liquid nitrogen users it is simple to respond to the conditions and include an inhibitor if needed. Not so simple for granular urea, which needs to be protected before it is delivered. More people are opting for protected urea – with a urease inhibitor impregnated or applied to the fertiliser prior to bagging.
Protected urea offers benefits in terms of performance over untreated urea – increased efficiency of nitrogen will inevitably reduce the amount of N needed to meet the optimum nitrogen supply.
Therefore, the fact that legislation is telling us that urea can be inefficient – gives us the opportunity to learn how to make it as effective as possible. This is important, given the reduction in the amount of ammonium nitrate that is available for the UK farmer.
The use of methylene urea products as a source of foliar nitrogen is a very effective way of maintaining nitrogen uptake through dry periods. Bypassing the soil and supplying a source of nitrogen that is safe and highly efficient offers further opportunities to rely less on conventional nitrogen fertilisers.
