Getting the most out of the nitrogen applied to crops is important both for farm profitability and sustainability. Low rainfall, dry or drying soils, warm soil temperatures – all of which have been widely experienced this season – or high soil pH are the environmental conditions which can increase the risk of ammonia and therefore nitrogen losses, from both granular and liquid urea fertilisers. The use of a urease inhibitor, such as BASF’s new product Limus®, can reduce these ammonia losses by up to 98%.
As part of a series of trials with its customers, BASF and Bartholomews Agri Food Ltd have joined forces to carry out 5 Agronomics on-farm, tramline trials, comparing two granular nitrogen sources: urea treated with Limus®, known as protected or inhibited urea and ammonium nitrate; in winter wheat and barley crops.
Andrew Stilwell, Agronomist and Crop Nutrition Technical Manager with Bartholomews Agri Food Ltd said, “We have 5 trials spread across 5 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.”
The trials have been set out using ADAS’s Agronomics methodology, which provides the protocols, software and statistics to enable farm trials to deliver robust and scientifically credible conclusions. Deep core nitrogen analysis was carried out before the trials began. These showed the background nitrogen levels were lower this spring than in previous springs, due to the amount of rainfall over the winter.
Mr Stilwell said, “I have taken samples for tissue analysis, in the season, 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.
“Later on in the season 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 are neck and neck. We couldn’t see any real difference between the two based on the tissue analysis.”
Dan Willis (FC Cummins + Sons), Rookery Farms, Berkshire has a trial on his farm and has also used Limus® protected urea over 520 ha of his crops.
Mr Willis said, “This is the first season we have used Limus treated fertiliser. Mr Stilwell has done tissue testing in the trial, so we have been able to keep an eye on nitrogen uptake from both the Limus protected urea and the ammonium nitrate, and with both, the plant has always had enough nitrogen.”
Mr Willis admits that using Limus® protected urea over such a wide area was a leap of faith, however, he 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. Mr Willis said, “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 is confident that he is getting full efficiency from his applications of Limus® protected urea.
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. Urease inhibitors delay this conversion by binding to urease enzymes, giving time for the urea to be washed into the soil.
Limus® is the only urease inhibitor available with two active ingredients, enabling it to bind to a wider variety of urease enzymes and more effectively minimise losses.
Mr Willis said, “We are very much in favour of a little and often approach so we will split our nitrogen 5 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%. That’s testament to not only getting the nitrogen on at the right time but using the right product too. We’ve pencilled in some more for this season coming.”
Limus® protected urea is available from Bartholomews Agri Food Ltd, COFCO International and Thomas Bell & Sons Ltd (Diamond Fertilisers).