11 May 2001
Sulphur in spuds needs more work

By Andrew Blake

LARGE-SCALE trials are needed to get to the bottom of the true value of different sulphur products for potatoes, believes John Ward, research manager at the Scott Abbott Research Station (SARS).

Signs of useful responses to sulphur, irrespective of its effect on common scab, emerged in a trial at the Peterborough site last year.

Last seasons SARS trial, to examine the effect of extra sulphur on common scab levels, involved watering a solution of Thiovit on to the tops of the ridges of Maris Piper plots immediately after planting.

Unfortunately there was very little scab in the control plots so we didnt notice any reduction in infection from the Thiovit and the trial was effectively inconclusive, says Mr Ward.

However, we did pick up an interesting, though not quite statistically significant, yield effect.

Output in the control plots was 62.4t/ha.

Where we used the Thiovit we got an extra 3.23t/ha of total yield, but more importantly 3.93 of saleable yield, because there were more larger tubers.

The result is the mean response from applications of 25, 50, 75 and 100kg/ha of sulphur, he says.

Debate over how requirements should be applied to acidify the soil and counter scab continues.

However, carefully scheduled irrigation, where available, in the six weeks from tuber initiation is a much better method of control.

Ammonium sulphate fertiliser is an obvious source of sulphur for the crop.

It has been known about long before I was ever at college. Anything which causes acidity is beneficial in overcoming common scab.

Other more recent options include Thiovit, Brimstone 80 pellets and New-Tritions newly imported SulFer 95 prills, and Omex suspension fertiliser.

With plantings seriously delayed this season, any sulphur applied will have to act fast, advises Mr Ward. There is going to be very little time to acidify ridges.

I am not yet concerned enough to want to use ammonium sulphate here.

“Our farm manager is more keen on urea with ammonium nitrate for late top dressing. But I do intend to repeat the experiment with Thiovit and will also try New-Tritions prills.

However, what we really need is quite a large experiment where there is known to be a bit of sulphur deficiency and on some slightly higher pH soil to test all the options.

“It would be a very useful exercise for BPC to put a bit of money behind.

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