Getting the most out of the nitrogen applied to crops is important for farm profitability and sustainability.

But low rainfall, dry or drying soils, warm soil temperatures – all widely experienced this season – or high soil pH are environmental conditions which can increase the risk of ammonia and nitrogen losses, from both granular and liquid urea fertilisers.

However, the use of a urease inhibitor, such as BASF’s new Limus, can reduce ammonia losses by up to 98%. It and Bartholomews Agri Food joined forces to carry out on-farm tramline trials, comparing two granular nitrogen sources – urea treated with Limus and ammonium nitrate – in winter wheat and barley crops.

Andrew Stilwell, of Bartholomews, said: “We have five trials spread across five counties, over a wide range of soil types, ranging from sands and gravels, to heavy clays and silts, the cumulative size of which is in the region of 60 ha.”

Deep core nitrogen analysis was carried out before trials began. These showed background nitrogen levels were lower this spring than in previous springs, due to huge rainfall over the winter.

Mr Stilwell said: “I took samples for tissue analysis at GS 32 and at GS 39, looking at both macro nutrients and trace elements. At GS 32, the ammonium nitrate plots were a little bit darker green than the Limus protected urea plots.

"However, within the plant tissue itself, looking purely at the nitrogen content, the two treatments were actually very similar. The subtle difference in appearance was not reflected in what we found with the tissue analysis.

"When we took the second set of samples at GS 39, there was no visual difference but the balance had changed slightly. The nitrogen content within the plant tissue was slightly more where the Limus protected urea had been used, as opposed to the ammonium nitrate.

"The net result of it was that the two products were neck and neck. We couldn’t see any real difference between the two based on the tissue analysis.”

Dan Willis, of FC Cummins and Sons, Rookery Farms, Berkshire, has a trial on his farm using Limus protected urea over 520 ha of his crops. He admitted that using it over such a wide area was a leap of faith,but said: “I can honestly say we have seen great results this year. Even with the dry weather its absorption has been absolutely fine.”

With spring 2020 likely to be declared as one of the driest on record, Rookery Farms have had very little rain, 22 mm, from the first week of March onwards. He added: “We had really hot weather through April with a warm wind all the time, what moisture there was dried off. I have always been very dubious of using urea because of the drawbacks in its ability to get into the soil, and the fact that it is so temperature orientated.”

Conditions have been textbook for ammonia volatilisation losses from urea, but Mr Willis was confident that he was getting full efficiency from his applications of Limus-protected urea.

Mr Willis said, “We are very much in favour of a little and often approach so we will split our nitrogen five ways from mid-February onwards on the winter wheat. The Limus-treated urea has given us a slow and steady uptake, which has been really good, so it has made use of every bit of moisture that we have ever had.

"All our wheat is for milling, we’ve N tested some of the ears and we are seeing great results there. It‘s looking like we are on course to hit our target of 13% protein."

Urease inhibitors reduce ammonia losses by temporarily slowing down the conversion from urea to ammonium, a process carried out by urease enzymes.

This process raises the pH of the soil around the urea and ammonia volatilisation can occur if this pH spike is not buffered by sufficient rainfall. This delayed conversion by binding to urease enzymes, gives time for the urea to be washed into the soil.