Holkham Estate in north Norfolk successfully grew a 10ha field of salad potatoes with zero synthetic fungicide, fertiliser or insecticide applications, without any loss in marketable yield.

Harry Barnett, potato manager at the estate, notes that five years ago he would have considered such a thing “impossible” and “commercial suicide”.

“If it went horribly wrong, the risks involved with cutting out inputs would potentially see our business lose a six-figure sum across just a 10ha area of potatoes,” he says.

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But thanks to high attention to detail and a keen eye ensuring crops remained healthy throughout the growing season, the trial was a success.

Compared with the farm’s conventionally grown crop, the trial revealed no difference in marketable yield and came with a significant cost saving of £400/ha.

How was it achieved?

A new Dutch-bred salad variety with strong agronomic traits and high blight resistance was grown.

“For context, on a conventional salad potato crop we would usually apply eight prophylactic fungicides to keep blight away, a soil-borne fungicide to control soil pathogens such as rhizoctonia and black dot, and an artificial blend of fertiliser containing di-ammonium phosphate, ammonium nitrate and muriate of potash,” says Harry.

The crop was planted post-cereal, but on land with a history of outdoor pig production, with good level of nutrients in the soil.

A carbon-based fertiliser supplied by CCM technologies, which claims to have an 80% lower carbon footprint than conventional fertiliser, was applied.

This came at a marginally more expensive price a tonne than standard fertiliser. It was applied in pellet form with a fertiliser spinner.

Although Harry notes due to its light nature, it was difficult to spread.

After the success of the trial, Harry planned to scale-up its area, but there have since been reports of the Dutch variety breaking down to a new strain of blight in Europe.

This has so far not been identified in the UK, but nevertheless Harry is reluctant to expand the acreage due to the huge gamble on the business.

“If you get blight in a crop in the early days it is a huge risk. You’ve spent so much money establishing a crop – incurring thousands of pounds a hectare. It certainly takes a lot of bravery to change the system.”

The plan is to roll out the trial across another 10ha this year.

“I am fully aware this is a small step and only represents a tiny fraction of our growing area, but this is progress. Farmers need realistic tools to move in a sustainable, dare I say, regenerative direction.

“The tools are slowly emerging and it is important for us to remember these things take time, and as a farmer you get one chance per year.”

Potato production

Over the last decade, Harry has reduced nitrogen fertiliser use by one-third on salad varieties at the estate.

Rates now range from 90 to 120kg N/ha, depending on variety, highlighting that change can happen if you put your mind to it.

About 80 to 90% of Holkham’s potato crop follows a multispecies cover crop mix including radish, phacelia, linseed and vetch.

This is sprayed-off and in some cases grazed with sheep, before being cultivated with an inversion cultivator. Ridging, de-stoning and planting follows.

The estate grows 25 varieties across a range of crop types including salad, main crop, processing and seed.

All of the crop is irrigated, excluding seed varieties. This involves applying 15cm (6in) of water to the crop each year.

A diverse six course rotation encompassing: potatoes, winter barley, oilseed rape/vining peas, winter wheat, sugar beet and spring barley is used.

This year, Harry is trialling for the first time growing potatoes in a 12-year rotation, replacing with onions.

“This should reduce the need for nematicides to control potato cyst nematode. Leaving fields free of potatoes for more than 10 years should significantly reduce pressure,” he says.