Growers looking to cut back on fertiliser rates next spring because of the high prices are being advised to take a field-by-field approach.

Last year, fertiliser costs averaged about 65p/kg of nitrogen and the best-case scenario for those who ordered earlier this year is 80p/kg of nitrogen (June price), says Ceres Rural partner and agronomist Jock Willmott.

However, those who put off buying this summer thinking prices would ease are now looking at more than £2/kg, he says.

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Based on average yields for 2021 and at current feed wheat prices (Nov 2022), farmers buying at £2/kg will see gross margins squeezed by £329/ha.

“This is a significant hit,” he says.

“So unless farmers have bought all their fertiliser at under about £1.10/kg of nitrogen, we are probably looking to reduce rates, especially if grain prices come under pressure and spring nitrogen prices either remain high or delivery is an issue.”

Maximise yields

Yield will be a key factor, he says, highlighting that farmers cannot afford to have a poor harvest in 2022.

Looking at the projected gross margins with fertiliser costed at £2/kg, the difference between a low-yield harvest (such as 2020) and a high one (sush as 2019) equates to a £463/ha difference in gross margin.

How much to cut by

Looking at the Niab economic optimum table, if farmers bought fertiliser at £1.05/kg, they are only looking at a 10-20kg/ha reduction in nitrogen at current wheat prices, so they really don’t need to do anything unless commodity prices drop.

For those who bought at higher prices, they will need to trim rates. But to deliver a significant cost saving, he says rates will need to be reduced by 30-60kg/ha of nitrogen.

For example, cutting rates by 40kg/ha over a 300ha area saves roughly £22,500.

Target fields

Rather than making blanket cuts, he believes the best strategy is to target nitrogen where it is best used, thereby maximising responses.

Looking at nitrogen response curves for 25 sites in wheat, there is considerable variation in response, as utilisation within the crop is influenced by so many factors – drilling date, soil structure/fertility, temperatures, moisture etc.

For example, the curves show that trimming rates in lower yielding fields will see less impact on yield than those fields with the big yields.

Therefore, he believes farmers should target less-responsive fields and varieties.

Timing

Timewise, he advises against doing it for the first pass, as this one is important for building the canopy and mitigating against potential early drought.

“Then later in season when we know what the wheat and fertiliser prices are doing, this is when to make the decision.”

Also, farmers will then know if a field is going to be 8t/ha rather than 12t/ha, so are able to prioritise trimming rates on these lower potential fields.