New study on optimising nitrogen applications to maximise profits published

At what point does the cost of N fertiliser negate the profit from a greater yield?

As the energy crisis begins to bite, driving fertiliser prices to new unforeseen heights (with no peak yet reached), part one of a two-part study, funded by AHDB and complied by ADAS, has just been published to help arable growers and advisers decide if a reduction in N applications will help their overall profitability and by how much they can potentially reduce by.

The goal of the research is to find the ‘economic optimum’ – the break-even price point at which the value of the extra grain is cancelled out by the cost of the extra N applied. The results should help growers optimise their nutrient management plans before applications begin in the spring.

The research brought together past N response curves for three crops: wheat, barley and oilseed rape. The results indicate that if grain and rapeseed prices were held at £200/tonne and £500/tonne, the optimal reduction in use of ammonium nitrate fertiliser due to its price doubling from £345 to £690/tonne would be 50 kg/ha N. The resulting impacts on yields would be small, -0.36 t/ha in cereals and -0.16 t/ha in oilseeds respectively.

The review also assessed the way current price adjustments are listed in the RB209 and whether new evidence required a recalibration.

“However, the sharper shape of barley’s response to N was not entirely convincing from recent trials results, so we concluded that adjustments for the high prices should remain the same for both barley and wheat” said Roger Sylvester-Bradley, who led the study.

The second half of the review is due in January 2022 will look at a wider range of arable crops, how N should be prioritised if prices remain high and the long-term implications for fertiliser rates and N management.