27 March 1999

SUSPENDED BELIEF

Suspension fertiliser is going west. Lucy Stephenson reports on one Herefordshire potato growers experience.

A LOOK-SEE trial last season at Willie Chases Tyrells Court Farm, near Leominster in Herefordshire was enough to convince him of the benefits of suspension fertiliser. He is cautious about the yield boost of 20% based on a single year, but is convinced about the convenience of using this type of fertiliser on his potato crop.

Each year, Mr Chase rents new land for his potatoes so production is spread over a wide area. This is why suspension fertiliser is so useful – it is delivered to the fields where and when required. Mr Chase pays for what he uses, saving an estimated £12.40/ha (£5/acre) in storage and handling costs.

The labour thats freed up by using contractors and their equipment is also a big benefit at such a busy time of the year. In addition to the saving in handling costs, last year the liquid fertiliser was about £12.40/ha (£5/acre) cheaper than granular fertiliser according to Mr Chase.

The right contractor is crucial to the operation admits Omex Agriculture, the company manufacturing the suspension fertiliser. Reliability and accuracy of application are vital so the contractors are especially selected for the operation, stress the company.

Until now Omex Agriculture have operated in the eastern half of the country because of the locality of its factories at Bardney in Lincs and Kings Lynn in Norfolk. There the product is applied to over 40,000ha (100,000acres) of potatoes.

Transporting suspension fertiliser across the country from the two factories in the east would be prohibitively expensive. However, plans to extend production to a factory in the west, once there is enough demand, could put suspension fertiliser on the national map. So a local Omex Agriculture agent is working with potato groups such as that run by Mr Chase to create demand.

He grows 100ha (250acres), but markets potatoes on about 300ha (1000acres) for 20 other growers. Estima is the dominant variety because it is a popular baker with the supermarkets, being close to the ideal 284g (10oz) size with few skin defects. The potatoes go into cold storage and are sold on a fixed market plan to supermarkets from November to July.

Suspension fertiliser has to be applied by a contractor for technical reasons. They use a specialist pump, with 3in piping taking the suspension to 1.5in pipes along the booms. "Its a bit like trying to spray masonry paint – its thick stuff," says David Lines, arable specialist at merchants Midland Shires Farmers, adding: "If you tried to apply it with a normal sprayer the sheer weight of product in the booms would make them fall off."

Accuracy

Using a contractor who will supply an application report and sample analysis also provides accurate traceability. "We have to farm to what supermarkets require," points out production manager Mark Hammond. "Youve got to apply just whats needed and no more."

In the Tyrells Court farm trial, one application of the suspension containing 213kg/ha (170 units/acre) of N and P and 288kg/ha (230 units/acre) of K was contractor-applied at planting to 8ha (20 acres) of Estima. At the same time, another 8ha (20 acres) received granular fertiliser of the same specification. Both areas also had around 7.3t/ha (3t/acre) of chicken litter and 24.3t/ha (10t/acre) of FYM.

As well as the trial areas, suspension fertiliser went on to half of Mr Chases own crop. "The suspension was a prescription mix," says Mr Lines. "The fields were sampled, and the fertiliser requirements matched to the particular variety, taking into account the FYM applied."

Spraying fertiliser as a suspension is more accurate and gives more even coverage compared to granular fertiliser, he reckons. Omex acknowledges that spreader technology is good but asks how many growers really apply granular fertiliser properly?

Another benefit of the suspension product is that can also be customised to contain products, such as sulphur or zinc for scab control, or herbicides. There are a number of tank mix recommendations.

A nitrification inhibitor, Didin, which slows the release of nitrogen was used in the suspension last year. It helped keep the crop greener for longer, says Mr Lines: "Many potato crops senesced earlier than normal because of the wet weather and lack of available nitrogen in this area," he says.

Three samples digs, each three metres long, were taken from both trial sites. The suspension-treated samples showed a spectacular yield increase of 13.62t/ha, or 22.5%, over the plots treated with granular fertiliser.

If the response is typical for a whole field it would have increased turnover by over £2000/ha with potatoes at £150/t last year. At December 98 prices of £350/t for bakers the increased turnover would top £4,700/ha.

The result has encouraged Mr Chase to use the suspension on all his potato land. Many in the potato group are now taking a keen interest.


Average total yield (t/ha) Saleable yield (t/ha)

Suspension fertiliser 80 74

Granular fertiliser 70 60

% increase 15.1 22.5


&#8226 Pay for what you use

&#8226 Even fertiliser application because sprayer-controlled

&#8226 Correct balance of nutrients

&#8226 Vary nutrients field by field

&#8226 Fewer passes because can add trace elements or herbicides