A project in Devon has helped farmers save thousands of pounds by fine-tuning their use of fertiliser. 

The soil mineral nitrogen (SMN) project saw analysis and review of nitrogen application across more than 425 hectares in the Otter catchment.

By reducing nitrogen use, farmers have saved an average of £234 per field.

The project is funded by South West Water (SWW) and delivered through Westcountry Rivers Trust (WRT).

WRT’s farm advisor Yog Watkins said: “Our 2022 SMN project assisted several farmers in the Otter catchment in conducting analysis to support their on-farm efficiency, while also making good business sense.

“Following a review of their likely nitrogen application plans for the growing season and how much these had been adjusted due to cost, we shared the results of their SMN test to enable further application adjustments up or down.

“One of the larger farms has already tested all of its arable fields this year and adapted the application strategy to limit any environmental impact and save cash.”

More than 425 hectares of conventional and organic land has been tested, all within SWW public water supply safeguard zones, which are the most vulnerable to nitrogen losses and have the greatest bearing upon public water supply.

A total of 79 fields were analysed: 50 per cent arable, 33 per cent grass and the remainder forage cropping (mostly maize). Data shows significant reductions in nitrogen applications, with the majority coming from the arable fields.

Total applications across all the fields fell from more than 57,114kg Nitrogen (N) to 49,521kg N, with 2,632kg N of this due to the high price of N and 4,961kg N due to adjustments based upon the SMN results.

With ammonium nitrate (AN) fertiliser costing £841/tn (£2.44/kg N) in July 2022, the savings equated to more than £18,500 with an average saving per field of £234. 

Arable savings were considerably more at £340/field, £148/field for forage and £113 for grassland, with one field’s savings more than £1,350.

A 7,593kg N reduction in application is the equivalent of 22tn of AN fertiliser.

The amounts saved are before sampling costs of £121.40 per field (which can be reduced further if carried out to a shallower depth).

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Better financial gain for grassland may be possible if testing one field in a block of the same soil, topography and management as a bellwether to adapt N applications across the whole block.

Yog added: “These are unprecedented times in farming and costs are volatile, so it is good practice to monitor efficiency across farming systems.

“Through the project, we have learned targeting testing to the higher N application fields first will provide the biggest potential savings.

“Fine-tuning nitrogen applications can save farmers significant money, while also avoiding fertiliser losses to the environment – it’s a classic win-win, as the farmers save and SWW saves in water treatment costs which should result in lower water bills.”