Seed potato expertise spells success

Specialist seed potato grower Tony Bambridge's field team has been making the most of the almost ideal spring conditions to get planting across Norfolk.

Since the seed potato business started 18 years ago, it has grown to about 340 acres of production under the B & C Farms umbrella from the base at Wood Farm, Marsham, near Aylsham.

It is highly-specialised because the aim is to plant at much greater density than a crop producing potatoes for human consumption.

Mr Bambridge's team, which includes his son, James, and Ian Durrant, who drives the three-bed planter, have been working flat out in the past three weeks.

The planter, which can set a maximum of 25 acres of potatoes a day, will place three rows in each of the three beds.

"Growing seed potatoes, these are planted at a much greater density than a main crop," he said. The aim is to get the potatoes four inches into the bed and then equally spaced across the rows.

"We plant all sizes from 25mm up to 60mm diameter tubers.

"They are the size range that we plant. If you're planting smaller potatoes, you have to plant at a higher density than larger potatoes because there is a correlation between the size or the weight of the tubers and the number of stems it will produce.

"So, a 25mm tuber will probably only produce one stem while a 60mm tuber may produce seven or eight stems.

"There is a reason why stems are quite important. There is quite a strong link, although it is not a linear correlation between the number of stems and the number of tubers produced. So, if one particular cultivar, on average, produces two and a half tubers per stem, and our objective is to harvest one million tubers per hectare, then you need 400,000 stems to get your million," said Mr Bambridge, who got his first certified seed crop in 1989.

"Different cultivars produce a different number of stems and also varying number of tubers per stem.

"It is not quite a mathematical equation because if you create more stems per hectare, the tubers per stem tend to decline because you get shading."

In a field at Weston Longville, the B & C Farming team was planting 35 to 40mm Estima on the farm owned by Peter Thomas.

"We want to produce a nice even size seed potato, which will go to produce the potatoes for consumption the following year," he said.

As a seed specialist, potatoes have to be grown on "clean" land. First, after cultivation, the field has to be ridged and then allowed to dry out before the de-stoner comes into action.

Then, once the clods and stones have been thrown between the ridges, the planter goes into action.

The aim is to produce a high quality seed potato, said Mr Bambridge, who is a former chairman of Greenvale AP Growers.

"We want an even run of seed. Farmers have different preferences but really between 30 and 55mm is about the size that most like their seed.

"Some have a preference for slightly bigger.

"It is interesting that farmers preferring bigger seed tend to be on the fens. They have a belief that bigger seed will survive a frost better and provide more vigour.

"Sand land farmers as a general rule tend to prefer smaller sizes because they feel they get a more even plant and a more even crop. And the more even you've planted, the more even ware crop you'll produce.

"And really, we're trying to produce ware potatoes either all small potatoes to put in punnets or all big potatoes for bakers or processing.

"The bit in the middle, while it is saleable and goes in the standard 2.5kg pack in the supermarket, it is not the premium market.

"Bakers, punnets or the big processing potatoes earn the bonuses," said Mr Bambridge.

And, there is a different discipline to seed production.

"We lift them earlier in order to avoid picking up diseases. And the biggest factor is fungal disease - not blight.

"Blight is controlled by the use of agro-chemicals but fungal disease is a direct correlation, the longer the seed tuber sits in the soil, the more diseases it will acquire because many of the fungal pathogens are actually soil-borne.

"That is important why seed has to be grown on clean ground.

"We anticipate dessication, starting with that crop in the first 10 days of July.

"As soon as the skins are set, then they will be lifted.

It it is important to have full skin set because the skin of the tuber protects it from disease. It is a bit like our skin, said Mr Bambridge.

Once lifted, it will be graded, boxed and stored at a controlled temperature ready for planting next year.

Plant health inspectors inspect the growing crop twice and then each seed lot is inspected on a further two occasions to ensure farmers get a quality seed product.