SULPHUR SCORES OVER COMMON SCAB

7 November 1998




WON OVER BY FREE SAMPLES

With the pressure on to maximise returns from potatoes, Lucy Stephenson reports on field trials

of two products claimed to improve returns.

THE 15% increase in potato yield seen in this years free trial of Fulcrum CRV so impressed George and Ben Atkinson they are going to buy the product next year.

Crops has been following the trial of potato growth stimulant Fulcrum CRV on the Atkinsons farm near Bourne, Lincolnshire, since June this year. The final harvest showed a yield increase of 15% on treated areas of Maris Piper.

A single application of 30 litres/ha was applied to two one-hectare sprayer strips, on 22 May, when the crop was 5-8cm high. Growth was monitored by Iain Turner, director and field trials manager of Levington Agriculture, who took eight sample digs in both treated and untreated areas, three times through the season and once at harvest.

Nousheh Ghadiri, technical adviser with Cargill, which markets Fulcrum CRV, explains the results.

"There was a 12% increase at the first dig on 14 July, and the digs at the beginning and end of August maintained that differential. At harvest we saw a 15% increase in yield – around 9t/ha, which gives an increased net profit of £1,133/ha, based on a Fulcrum application cost of £60/ha and a selling price of £132/t" she says.

Crucially, about two-thirds of the increased yield was in the pre-pack and baker sizes, from 50 to 70mm. "The tuber crop bulked much faster so there was the option to lift earlier to catch the early market with a high yield," she adds.

The flexibility in lifting date has another advantage – says George Atkinson. "The field we did the trial on was grade 1 silt but on heavy land, lifting late would be a problem."

"We were quite sceptical from the start – the results have surprised us. Id definitely buy the product. Id like to do a bigger trial next year," he adds. Ian Richards, Levingtons managing director, says: "Over the years there have been a lot of products, which are not straightforward fertilisers, which have some effect on yield. But this is the first time Ive seen one that – not always, but consistently – gives a positive result. Theres a definite trend coming out at a 12-15% yield increase.

"About 50% of Fulcrum is molasses, and the rest is a combination of 28 different nutrients and trace elements," says Ms Ghadiri. "You put Fulcrum on at stolon swelling stage when theres really rapid cell division; 80% of what you put on is sucked in, and increases the number of cells. We saw a response between three and 18 days after emergence. Cara is the only variety where a second application would be useful, since it throws out stolons throughout the season."

Because Fulcrum CRV is applied as a foliar spray in the UK, it contains an adjuvant called Crovol to help take-up by the leaves – hence CRV. But the product can still be taken up if washed into the soil.

SULPHUR SCORES OVER COMMON SCAB

USING sulphur to reduce the level of common scab may be an unfamiliar tactic but a Lincolnshire consultant has managed to halve scab incidence in a trial with sulphur prills.

Robert Boothman, whose family company advises about 60 potato growers in south Lincolnshire and north Cambridgeshire, arranged the trial locally after hearing about Dutch experience showing significant reductions in scab when Tiger 90 sulphur prills were used.

He set up the trial on R Bratley & Sons farm at Quadring, Lincolnshire. "Bratleys were keen to achieve a pre-pack sample," says Mr Boothman. "With the Tiger 90 in Horstine Farmery hoppers, we used a 14mm deep fluted rotor to meter out 50kg/ha onto the top of the ridges. Bratleys have a total of about 75ha (185 acres), and we treated areas of between 1-2ha (2-5 acres) in the middle of each field soon after planting.

"The idea is that rain washes the sulphur into the ridge in a narrow band around where the potatoes are going to grow. Just after desiccation we went in and pulled up 10-15 roots in each of the treated and untreated areas. We saw a 50% reduction in scab, from 30% in the untreated areas to 15% in the treated areas," he adds.

While this is a significant result, it is not sufficient to move all Bratleys potatoes into the pre-pack market. "If you started off at 15% scab and got down to 7.5%, then youd start to get into the second-class pre-pack markets, which would give approximately a £50/t premium. If you started at 7% scab and moved to 3%, you could get into the first-class pre-pack market, with a further £50/t premium. The potential benefits are massive," says Mr Boothman.

Elemental sulphur is relatively stable, and unlike the leachable sulphates usually found in fertilisers, this form must be weathered first. "If wed used any other type of sulphur, it could leach through too quickly, but the form we used is so stable you really do need a lot of moisture to get it mobile. When it breaks down it turns into a weak concentration of sulphuric acid, and scab wont develop readily in acid conditions," he says.

"If you buy sulphur as a fertiliser and apply it to the whole field the effect is very much diluted. What were trying to do is drop the pH in a small area, around the potato. Stefes say the localised pH drops about one pH point.

"The soil type we had in the trial was a good quality, free-draining silt loam. If it had been a heavier soil type it would have been better to put the prills in the soil before the potatoes were ridged up, so that they were a bit lower down."


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