Leading Kent potato business St Nicholas Court Farms is boosting the high-value baker fraction in crops of Estima by using seed of a known age.

Although many growers are aware that manipulating the planting date of seed crops can help produce tubers better suited to market demands, few are putting that knowledge into practice.

Graeme Skinner, who leads the agronomy team at St Nicholas Court and its Kent Veg co-operative group, is convinced of the technique’s value. He first came across Cambridge University Farm’s research in this area about four or five years ago through the University’s growers club, CUPGRA.

The findings suggest that the time-span between initiation of the seed tuber and its subsequent planting affect stem numbers in the resulting ware crop.

This means that ware crops grown from young seed produce fewer stems and therefore tubers, making it easier to bulk up tubers to the size needed for premium baker markets.

Mr Skinner realised such an approach could benefit his Estima crops, which had a short growing season. “The short canopy duration means we don’t get high yields – we average about 45t/ha – and struggle to get tubers to bulk up,” he says.

“As the crop started to senesce, quite often in mid-July, we didn’t have as many bakers as we would want, so we were extending the season, which increased our risk from black dot.”

Using Date-Smart Bold seed from Pseedco has allowed him to produce crops with fewer tubers and to get those tubers to reach baker size more quickly, compared with conventional seed.

“Instead of producing about 35-40% bakers, it’s now 60%.” That can increase overall market value by 10%, he says.

The other benefit has been a reduction in black dot levels as the crop spends less time in the ground.

St Nicholas Court Farms also uses Date-Smart Bold seed for some of its King Edward and Maris Piper crops. “King Edward has very high stem and tuber numbers, and we’ve been able to reduce the number of undersize tubers.”

These successes have encouraged Mr Skinner to increase his area of Date-Smart potatoes, which now account for more than 10% of the firm’s 486ha (1200 acres) of potato crop. “It has been steadily increasing. The limiting factor is how much seed we can buy.”

Practical challenges of producing date-smart seed

Pseedco produced about 15ha (37 acres) of Date-Smart Bold seed this season. The four different varieties used – Estima, Maris Piper, King Edward and Marfona – are destined for specific ware producers currently signed up to back-to-back contracts. It should be enough to supply up to 210ha (519 acres) of ware production in 2009, the firm’s Alistair Redpath says.

Growing Date-Smart Bold seed has its challenges, he admits, although one benefit is lower nitrogen costs.

Seed is typically planted in early July and harvested in October. “Much of the available soil mineral nitrogen has already mineralised and become available by the time the seed crop is planted,” Mr Redpath explains.

The biggest challenge is blight, particularly with Maris Piper and King Edward, says Mr Redpath. “The problem is the crop emerges at a time when there are mature crops all around.”

Crops need to be sprayed almost from emergence. But developments in blight fungicides over the past few seasons have helped, he says. “We see blight coming in early on occasions, but we can hold it. So far, we haven’t had any issues with blight in tubers.”

Another problem is that planting time has coincided with seed growers’ staff holidays, as the crop is produced “out of season” compared with most seed crops. Initially small production plots were located with several growers, partly to spread the risk from blight, but a few growers dropped out because of staffing problems, Mr Redpath says. “Now we’re trying to put larger plots out to make it a significant enterprise.”

The success of growers like St Nicholas Court Farms is encouraging Pseedco to increase its area next season. “We’re looking for new growers. We need some 40-50ha of production across three varieties, but particularly Maris Piper and Estima.” Less-responsive Marfona is likely to be scaled back.

Ware growers will pay about 10% more than for conventional seed, reflecting extra blight control and cold storage requirements. Returns for seed producers tend to be about 20% better than for a conventional seed crop, Mr Redpath claims.