Building tuber quality from the ground up

With input costs already under intense scrutiny, and nitrogen prices rising sharply following instability in the Middle East, potato growers are carefully examining every expenditure line.

Yet Tom Decamp, Crop Nutrition Business Manager at Yara, says evidence suggests growers targeting pre-pack quality are largely maintaining their traditional nutrition programmes and seeking savings elsewhere – in land rental decisions, machinery investment and contractor use. Simply because of the financial prize at stake.

"Potato growers may cut back a little on total nitrogen," Tom explains. "But they're still trying to achieve that premium over the general ware price, which can add £40–£50 a tonne to the return from a crop.

"If you are achieving a yield of 50 tonnes per ha, for example, this could potentially increase margins by around £2,500 per ha from achieving pre-pack quality. That makes the use of Tropicote — currently costing under £200 per ha — a sound investment as part of a potato nutrition strategy.

"And when it comes to getting calcium and plant-available nitrate nitrogen into the potato crop at tuber initiation, soil-applied calcium nitrate remains the most effective route."

Why calcium nitrate must go in through the roots – and early

The agronomic case for soil-applied calcium nitrate is rooted in fundamental plant science. Calcium is only mobile upwards within the potato plant, so the only pathway into the tuber is through the fine root hairs in the soil. Foliar calcium applied later to the canopy will stay within the canopy, enriching the foliage, but it cannot travel down into the developing tuber.

"When the tuber initiates, and it's just hooking over and booting up, that's when it's critical to get the calcium in," says Tom. "We've demonstrated this process using YaraLiva Tropicote and a red dye. You can see the calcium nitrate moving through the root hairs and flooding into the tuber, like blood through an artery."

Another key advantage of YaraLiva Tropicote is that it begins working immediately on contact with soil moisture, without requiring rain or irrigation to activate it.

"It works in cool, wet conditions as well as under drought stress conditions," adds Tom. "It doesn't have to go through the nitrification process – that all takes time. With YaraLiva Tropicote, the calcium and nitrogen are available straight away. Cool or dry, you will get uptake."

The recommended application is 400kg of YaraLiva Tropicote per hectare at, or close to, tuber initiation. At this rate, growers are delivering exactly 64kg of nitrogen per hectare – all in immediate, plant-available nitrate form – alongside 104kg of CaO, also instantly available. On timing, Tom is emphatic:

"You don't want to be moving way past tuber initiation because it becomes too late," he says.

Better structure, better skins – calcium's role inside the tuber

Once inside the tuber, calcium strengthens cell walls, providing the physical integrity needed to withstand the rapid growth spurts that occur during warm, moist conditions. Without adequate calcium, cells expanding too quickly simply burst.

"When the cell walls are not strong enough, they expand and burst — and that's necrosis," explains Tom. "They die, and that's the internal browning (rust spot) that triggers rejections at the packhouse and strips pre-pack growers of their hard-won premium."

The benefits of adequate calcium reach beyond internal quality. A stronger outer cuticle provides greater resistance to bacterial infections and skin disorders. Tom points to observed reductions in silver scurf and other skin complaints alongside improvements in storage performance, including reductions in soft rots. Calcium also builds stress tolerance: during dry periods where irrigation is unavailable, calcium-rich crops are better equipped to survive and recover.

"If they're looking at a sample and they start cutting them in half and there's internal rust spot, they'll get rejected – they won't get through for pre-pack and you lose your premium," says Tom. "Or if the skins are terrible, or they're all irregular sizes. Supermarket pre-packs might be four in a pack — everything has to be absolutely right."

The benefits of well-supplied calcium also carry through into seed potato production. A stronger, healthier mother tuber produces better quality seed for the following season, which is a consideration of particular importance in Scotland, where Yara is well established in the seed potato sector.

The insurance policy that pays for itself

Although some potato varieties carry a lower rust spot risk, and some seasons are kinder than others, Tom Decamp says the unpredictability of which seasons and varieties will be affected is itself an argument for applying Tropicote early and treating it as a non-negotiable part of the programme rather than a discretionary extra.

The arithmetic is unambiguous. A 50-tonne pre-pack crop losing its quality premium of £40 to £50 per tonne represents up to £2,500 per hectare forfeited at the point of sale. Against an application cost of under £200 per hectare for YaraLiva Tropicote – even allowing for today's elevated input prices — the potential return far outweighs the cost.

Growers spending on Tropicote are not paying for a product. They are protecting the premium that justifies their entire investment in the crop.

With the price of fertiliser subject to upward pressure due to geopolitical tensions in the Middle East, some growers may pause. But Tom's position is unequivocal:

"It's false economy not to apply the right nutrition if you're trying to grow a quality crop."