This is the best time of year to get out and look at soil conditions for potato crops, urged Mark Stalham of Cambridge University Farms at last week’s East Anglian Potato Event.

“You’re looking for any problems underground,” he said. “Potato crops root to a depth of 1m, but they are very sensitive to any compaction.”

In loose soil conditions, maximum root growth was 2cm a day, he said. “If there’s any soil resistance, it will limit how fast the roots can grow through the soil.”

Soil resistance could be measured quite easily, he explained. “There’s some hand-held equipment available that allows you to take an instant reading. This can then be used to decide what cultivations strategy to pursue.”

A reading of 3MPa (435psi) spelled trouble. “Roots simply can’t grow through that level of resistance at all.”

Where a pan needed breaking up, it was important to subsoil at or just below the pan, he said. “Go into the zone or very slightly below it. If you go deeper, you will simply lift the pan without busting it.”

Cultivations in wet soils should be avoided. “If the soil is below 26-27% moisture content, it’s fine to cultivate. But at levels above that, you get smearing and don’t get the benefit of fissure cracks.”

Autumn cultivations ahead of planting potatoes in the spring were often a waste of diesel, said Mr Stalham. “It’s usually better to come back in the spring.”

De-stoning did the most damage to soils, he said. “If you’ve got good soil structure with virtually no stones, and you’re planning to grow a seed crop, then consider omitting the operation completely.”