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Infra red scanning of manure could cut fertiliser bills

29 July 2011

Accurate, quick and potentially cheaper nutrient analysis of organic manures on-show at Grassland and Muck, will soon be helping potato growers shave thousands of pounds off their annual fertiliser bills and help protect the environment.

Although up to half the national crop receives organic manure of some type each year, relatively little is used effectively, says Ken Smith of ADAS, reporting on LINK-funded research.

He hopes the fruits of a three-year study using infrared scanning to analyse manures will change all that.

“You would expect to see considerable savings in nitrogen (N), phosphorus (P) and potassium (K) use on fields that have had manure compared with those that haven’t,” he explains. “However, annual statistics on fertiliser use show very little difference at all.”

It seems many farmers are either ignoring or underestimating the amount of nutrients supplied by manures, especially nitrogen. Dr Smith believes high analysis costs, long turn-round times (often more than two weeks) and sampling difficulties leading to unreliable results are part of the problem.

A survey carried out a few years ago showed that just 4-7% of farmers had any analysis of cattle farmyard manure (FYM) carried out, and only some 13% had dairy slurry tested. The figures are unlikely to have changed a great deal, says Dr Smith. Farmers could be up to 300% out on N supply calculations if they rely on ‘typical’ manure content, he warns.

Growers can use published estimates from the Crop Nutrition Guide for Potatoes and RB 209 8th edition, he concedes. “You can get a pretty good idea of P, K and Mg content from such sources, which are quite satisfactory for general planning purposes and to help establish and maintain a satisfactory soil status for these nutrients.

“But, for field level, crop-specific recommendations, particularly for nitrogen, these are not good enough. There is far more variance in N content of manures, and the paybacks in terms of crop yield are substantial if you get it right – but, conversely, the penalties can be high if you get it wrong.”

Dr Smith hopes the new technique using near infrared reflectance spectroscopy (NIRS) will provide farmers with a low-cost, simple and reliable alternative to conventional laboratory analysis.

“Rather than days, this test would take minutes – certainly a next-day service would be easily achievable. We want to encourage farmers to analyse and make the most of organic manures, which is good for their profits and for the environment.”

While the technology is proven – it is widely used in silage and grain testing – no recognised procedures or proven NIRS calibration models existed for manures to be assessed using the chosen NIRS scanner, a Bruker Matrix-I.

During the first two years of a three-year LINK-funded project, the project team collected and scanned thousands of manure samples and selectively analysed hundreds to allow the construction of robust calibration models for a range of manures and biosolids.

The NIRS procedure now produces excellent results for dry matter, total N, ammonium-N, total P and sulphur. While less accurate for minerals K and Mg (and pH), it may be possible to derive a good prediction based on dry matter estimates, he explains.

During the final year of the study, nitrogen release predictions were generated for different manures using the same NIRS procedure. Results show slurries release N quickest, with FYM peaking later and biosolids providing a more gradual, even release.

Used in conjunction with the widely used decision support system MANNER, which helps predict N losses after application, as well as a good soil analysis programme, the technology will deliver the strategies that will give farmers the confidence to cut nutrient rates with confidence – and their fertiliser bills too, says Dr Smith.

Gary Collins, the AHDB Potatoes nutrition specialist says all AHDB sectors are working to support the introduction of this new service, and details will be available shortly.

Visit the NIRS equipment in operation on the AHDB stand at Grassland and Muck, on May 18 and 19 at Stoneleigh Park, Warwickshire.

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