Potato yields can be boosted by using nitrogen inhibitors sprayed on to the soil or applied in-furrow at planting, according to independent on-farm trials in Scotland.

The nitrification and urease inhibitor Didin was used in the trials and works by slowing down the conversion of ammonium into nitrate, reducing losses by leaching and volatilisation.

The product contains dicyandiamide along with urease inhibitors and allows larger volumes of nitrogen to be applied at once, with the nitrate being released slowly as the crop grows.

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Independent agronomist and AICC member Hamish Coutts has been investigating the benefits of Didin, which is marketed by Omex, on two of his clients’ farms for the past three years.

Also in his trials were the plant growth promoter Biomex, which contains Bacillus amyloliquefaciens and various trace elements, and another bacteria, trichoderma, that is used as a biocontrol of soil pathogens such as rhizoctonia.

The effect of the phosphate/phosphite mixture Vigga – claimed to enhance plant rooting – and TPA, a phosphate stabiliser, were also investigated.

Didin was applied in-furrow at planting with all the crop’s nitrogen requirements in the form of liquid urea-ammonium nitrate (UAN) and Mr Coutts has seen an improved tuber size distribution and subsequent increase in saleable yield.

“Over the three years, Didin was the only product to produce consistent results and even in the wet season of 2012, when you would have expected increased nutrient losses, we still got a response,” he says.

“So from that perspective it is environmentally strong, too, as it is reducing nitrates entering any water bodies,” adds Mr Coutts.

Mr Coutts suggests the UAN formulation he is using to feed the potato crops is playing to the Didin’s strengths, as a majority of the nitrogen in the formulation is in the form of ammonium.

“It’s giving the product something to work on and applying them both together in-furrow at planting seems to give the best results,” he adds.

Continuing trials

On-farm trials are an important aspect of Mr Coutt’s agronomy service, allowing him to investigate the benefits of certain products using his customers’ own equipment and soils, instead of relying on external data.

He will be continuing to look at Biomex, but for this coming season will have the use of a Target Set Side Ridge Injection (SRI) machine that injects fertilisers and other liquid products straight into the side of the potato ridge.

Launched at the British Potato Event in Harrogate, Yorkshire, last year, the tractor-mounted machine is a joint venture between Standen Engineering and Target Set.

Mr Coutts hopes that getting the Biomex product into the ridge after the crop has emerged might produce better results than the in-furrow applications previously used.

“I’m hoping that getting the product around the growing tubers and roots will see a more consistent response than in previous trials,” he adds.