14 February 1997

Sulphur deficit found in spuds

SULPHUR deficiency in potatoes has been uncovered in trials on foliar feeds in Scotland.

The finding is a spin-off from testing potential foliar feeds on a site near Glamis, Perthshire, says Mark Ballingall, regional agronomist with CSC PotatoCare.

The work confirms fears of growing sulphur shortages north of the border, which until now have affected mainly oilseed rape and cereals, he says. "It has awakened us to the problem in potatoes."

Thirteen growth stimulants were assessed in replicated programmes applied to Estima for prepacking. "Undeniably the best results came from sound basic nutrition – and sulphur stands out," says Mr Ballingall.

Four fortnightly treatments of ammonium thiosulphate (as Cutonics SA60) applied from early bulking gave us an extra 10t/ha (4t/acre), he reports. "They also gave us a marginal improvement in skin quality. If we rate the control at 6 on a 1-9 scale the SA60 gave us a 7." The SA60 provided 13.6kg/ha of sulphur.

Magnesium sulphate, as Bittersalz which gave about half as much sulphur as the SA60, also produced a useful 5t/ha boost at slightly lower cost.

"The key point is that the trial had apparently adequate soil sulphur fertiliser of 99kg/ha of S."

Sulphur boosted yields in CSC trials, said Mark Ballingall.