Soil depth is key

Planting depth and soil type are two of the most significant factors when it comes to in-field tuber greening, an AHDB-funded study has found.

The project, carried out at NIAB CUF, looked at factors including tuber formation, stolon architecture and nitrogen rates, but concluded none of these was as important as the amount and type of soil above the potatoes as they grow.

Dr Simon Smart, research associate at NIAB CUF, said: “On sandy and peat soils, few green tubers were found with more than 2.5cm soil coverage but on clayey soils, green tubers were found with more than 5cm of soil coverage. Tuber greening was most severe on sites where more tubers were close to the soil surface and where the clay content of soil was higher.

“Unfortunately, planting deeper is known to delay emergence and therefore reduce yield, so growers must find the balance between achieving a high yield while also minimising tuber greening.”

Seven varieties (Estima, Jelly, King Edward, Marfona, Maris Piper, Markies and Melody) were grown in experiments over three years in Cambridge as part of the NIAB CUF research project. This investigated the relationship between stolon architecture and tuber greening.

Tuber greening is a big cause of waste costing millions of pounds each year. On average, 5% of yield is affected, but in the most severe cases, 20% is affected.

Factors known to influence tuber greening include row width, planting depth, ridge shape, soil cracking and variety. Dr Smart concluded: “Where tuber greening is substantial, growers should investigate where the green tubers are in the ridge – for example exposed at the surface, growing out of the flanks or unexposed, and adjust their planting depth and ridge geometry accordingly.”

The amount and type of soil above potatoes is the most important factor.