February 13, 2023 3:47 pm Published by LauraE
Farmer Story Urease Inhibitor

With Defra announcing new rules on urea containing fertilisers, such as UAN, urease inhibitors have become increasingly important. With OMEX’s own urease inhibitor, NitroShield able to reduce ammonia emissions from urea containing fertilisers by more than 70%, and increase yields and grain proteins by 0.3t/ha and 0.2% respectively, it has caught the attention of Lincolnshire arable farmer Mark Stubbs.

So much so, he has set up his own extensive field trials across more than 400ha of cereals to compare 50% untreated crop against 50% treated with OMEX Agriculture’s urease inhibitor NitroShield. Winter wheat varieties include the Group three Extase and feed wheat varieties Skyscraper, Cranium and Dawsum. The mostly chalky clay soils support yields of around 10t/ha.

“OMEX is not involved with our trial but we will share the results with them to compare notes,” he explains. “We have also considered other options for reducing nitrogen emissions including molasses formulation – but these do not have Defra approval – and amino acids but we have not seen any evidence to support their use.”

OMEX has conducted three years of its own rigorous NitroShield trials too. The product meets the government target of reducing ammonia emissions by 70%, when mixed with Nitroflo or Nitroflo S grades prior to application, which should help farmers grow crops more sustainably.

NitroShield urease inhibitors

“Urease inhibitors work by blocking the urease enzyme from hydrolysing urea, which causes ammonia losses,” explains OMEX technical development manager David Booty. “NitroShield has been specifically developed, and rigorously tested, to meet government guidelines on reducing ammonia.

Mr Booty recommends that NitroShield should be routinely used for all nitrogen applications after 31st March unless signed off as unnecessary by a FACTs qualified adviser.

“Rates can be reduced when soils are neutral or slightly acidic, or the crop canopy provides full coverage of the soil, the ambient temperature is not expected to be more than 15ºC within 24 hours of application, or a FACTS qualified advisor has recommended,” he says.

“Full rates should be used when soils are alkaline (pH >7.0), or when the crop canopy does not provide full coverage of the soil, or the ambient temperature is expected to exceed 15ºC within 24 hours of application.”

Mr Stubbs expects a successful outcome from his trials, with yields and grain protein both increasing, but he also says there should be a positive impact on the environment and an ability to extend his nitrogen application window, offering greater flexibility to the fertiliser regime.

Beaconsfield Farm, near Marshchapel has used OMEX liquid fertiliser for the last four years having switched from a granular fertiliser regime, with the help of local OMEX DSM, Dean Waddingham. The farm extends to 700ha including 280ha of cereals, 280ha of oilseed rape, 100ha of spring barley and about 40ha of rye. Yields and quality have steadily improved across the farm in that period. Four 55t OMEX liquid fertiliser bunded tanks are now positioned in the main farm yard.

Liquid fertiliser applications start in late February with the first of three liquid applications in equal splits of OMEX 22N+10S03 (Nitroflo 22+S) at a rate of 250L/ha. This replaces an early granular fertiliser 21N:60S03 application in February. The second and third liquid applications are applied at the end of March and April respectively, providing 69kgN/ha and 31kgSO3/ha at each application. The spray timings coincide around pesticide applications at GS30, 31 and 32.

“Applying the granular sulphur fertiliser in one hit meant a risk of losing much of the sulphur to leaching,” explains Mr Stubbs. “But, when applying sulphur along with the liquid nitrogen in smaller doses and more frequently, both elements are taken up more efficiently by the plant.  We are putting on half of the sulphur that we used to and getting higher yields.”

Mr Stubbs admits that if it were not for the Defra ruling he probably would not have considered using urease inhibitors. His own trials are not over a small area and his expectations are high.

“We know that we need to see an improvement in nitrogen plant efficiency, which can be partly achieved through reducing volatilisation. The Defra ruling has made me think of our options  ahead of the deadline,” he says.

“Due to the rising cost of fertiliser and pressure on yields, my focus has been increasingly on the roll of nitrogen in the crop growing cycle. We have found that too much nitrogen can have a negative impact on yields.

“Nitrogen will help a crop reach a threshold, but where on occasion we apply more than is necessary, yields have reduced by about 5%. We are trying to find the sweet spot,” he says.

Mr Stubbs has already decided to include Nitroshield on the winter wheat and oilseed rape in 2023 and possibly the spring barley, due to it optimising nitrogen use efficiency, demonstrating a 10:1 return in independent trials.

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