Sap trial to meet quality demand

23 April 1999

Sap trial to meet quality demand

RISING quality demands of potato processors led a Notts farmer to run an Omex sap analysis trial for the first time last year.

With a 20m gal winter-filled reservoir completed in 1997 ensuring his crop will not go short of water, it is now time to fine tune other factors, says Chris Lamin.

Four hectares (10 acres) in a 5.3ha (13 acre) field of Maris Piper at Starnhill, near Bingham, were sampled on three occasions to establish leaf nutrient profiles. Supplementary foliar feeds based on the analyses were then applied and the benefits checked at harvest.

If further trials are as successful as last season, the system could extend to the full 65ha (160 acres) of potatoes grown in a five-year rotation on the 485 ha (1200 acre) unit.

An Assured Produce contract with McCain company, PAS of Grantham, rewards crops with less than 10% defects and imposes increasing penalties above 12%.

"I am now looking to improve quality rather than go for volume alone," says Mr Lamin. Fewer outgrades or more yield are essential to cover the extra £76/ha (£31/acre) spent testing and treating the crop. This includes £90 to enter the sap testing programme and £40 for each additional site.

The first test is made two to three weeks after crop emergence, a second 14 days after treatment and a further one 14 days after the second treatment.

Leaf and petiole samples are taken, a supermarket bag full being plucked at regular intervals from three rows each side of a tramline. The samples are sent by overnight courier to Omex for a two-day turnaround analysis of 16 main and trace elements plus pH reported as low, good or in excess.

Last year the first analysis revealed low calcium which McCains research shows causes internal rust spot. Three applications of 2.5litres/ha of Calmax went on with the blight spray to address the problem.

Sulphur, manganese, zinc and boron were also identified as being low. A custom blended SAP mix was used to lift levels in a separate application. "The idea of a SAP analysis is to keep crop nutrition in balance not just to correct extreme deficiencies," says Mr Lamin. A later test found nitrogen on the low side and this was remedied with a spray of Omex Folex N.

The final SAP analysis indicated that nutrient balance had been improved by the treatments, and sample digs on two plots indicated a 13% yield benefit. A separate three-plot lift suggested a 19% increase.

"Staff on the harvester saw a definite visual increase from the treated area on a field that was struggling," says Mr Lamin. "This might prove useful following the difficult planting and soil conditions for some crops this year."

When it comes to rejects, high dry matters are unwelcome, he adds. "It makes tubers liable to damage at lifting." At 22.7% the treated crop was much closer to the ideal for maximum bonus than the untreated at 24.2%, he adds.

This year he plans to extend the trial to cover half fields of Maris Piper and Agria. &#42


&#8226 Quality demands rising.

&#8226 Leaf/petiole samples.

&#8226 Nutrient fine-tuning.

&#8226 Yield and quality benefits.

&#8226 May help stressed crops.

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