Farmers could significantly boost the size of their sugar beet by preparing the ground with cover crops, according to the initial results of a Norfolk field trial.

After last year's spring barley was harvested at Hall Farm, run by JE Spratt in Necton, near Swaffham, part of a field was left as stubble and another was planted with oil radish – a cover crop used to retain nutrients and moisture in the soil during the winter, improving its structure and fertility.

As the following sugar beet crop began to establish itself this summer, farm manager Kevin Banham said he was astonished at the difference between the plant growth in the two halves of his field.

And this week, when agronomy students from Frontier Agriculture dug up test plots either side of the divide, they found that the average beet size was 57pc larger.

The samples will now be sent for analysis at the British Sugar plant in Wissington near Downham Market, to see what the effect has been on sugar content.

Emily Page, a graduate trainee agronomist at Frontier Agriculture, said: 'Cover crops are not something you can harvest and sell. They are great for soil health, but because all that is going on underneath the ground it is still taken for granted, and unknown.

'So this is about getting the data to prove to farmers that we are starting to see the evidence that they will get the monetary benefits as well.'

Mr Banham added: 'The whole field was treated the same in respect of the base dressing, the top dressing and the fertiliser and herbicide. The only difference was the oil radish on this part of the field.

'Frontier marked out this area by satellite, but you didn't need a satellite to work out where it is, because the difference in growth is so pronounced. It is a dramatic difference.

'This is very light soil and very prone to winter rainfall, so you get that flush of water through the soil profile and you lose all those valuable nutrients. By putting in a cover crop you soak up the nutrients and you also get the roots helping the soil structure and improving the organic matter – and we got the weed suppression because we had a bigger canopy.'

Initial results

Four plots were dug either side of the divide between the cover-cropped beet and the side that did not have cover crops. 10 roots were lifted per dig.

The average weight of 10 roots from the cover-cropped side of the field was 11.15kg, compared to 7.1kg without cover crops.

But estimated plant population on the non cover-cropped side was 82,000 plants per hectare, with only 72,800 plants per hectare after the cover crop. The trial team believes this lower number is because the plants were so much larger on the cover-cropped side.