Impact of High Nitrogen Fertiliser Prices on Nutrient Management of Arable and Forage Crops

Keywords: nitrogen, fertiliser, yield, break even ratio, economic optimum N rate.

Nitrogen (N), phosphate (P₂O₅) and potash (K₂O) fertiliser prices are now three to four times greater than they were in 2020 and crop prices have almost doubled over the same period. This paper reports on analyses of recent N response field experiments to explore how changes in fertiliser and crop prices affect the economic optimum N rate for arable and forage crops, together with implications for crop quality and recommendations for nutrient management. The new evidence analysed: 46 experiments on winter wheat, 6 on winter barley, 11 on spring barley, 12 on winter oats, 12 on spring oats, 22 on winter oilseed rape and 22 on grass, indicated that it is reasonable for N recommendations to be based on different N response curves for i) wheat and barleys, ii) oats, iii) oilseed rape and iv) grass. Increasing fertiliser prices relative to crop prices result in a lower economic optimum N rate for feed wheat, barley, oats and oilseed rape. During 2022 the break-even ratio (BER) reached 10 for cereals and 4 for oilseed rape, compared with longstanding BERs used in N recommendations of 5 and 2.5 respectively. These were estimated to reduce the optimum N rate by 50 kg/ha for feed wheat, barleys and oilseed rape and 25 kg /ha for oats. For milling wheat, it was generally considered to be economically justified to maintain N rates, especially with milling premiums of at least £30/t. It was concluded that recommended N rates for grass should also be maintained because they are set at levels that still make grazed and cut grass the cheapest form of forage. However, purchasing fertiliser at higher prices represents a higher business risk, and cash flow on many grazing livestock farms may not allow it.

The value of more precise N application increases as fertiliser prices increase. The new prices therefore have increased the importance of i) estimating soil N supplies as accurately as possible, ii) maximising the benefits of organic materials e.g. by knowing their nutrient contents and how much is applied, iii) making use of proven technologies for maximising the precision of N applications and minimising N losses to the environment, iv) optimising levels of non-N nutrients, soil pH and soil structure to maximise N use efficiency. If N fertiliser prices cause growers to reduce fertiliser N use for an extended period, the soil N supply in rotations with a high proportion of N-fertilised crops is likely to reduce as the balance of N inputs to offtakes becomes smaller, and the effects of this will accumulate over years.