Adjust your tackle now for a spot-on spread, says IMATS

7 February 1997

Adjust your tackle now for a spot-on spread, says IMATS

By Robert Harris

AS the annual top dressing frenzy draws near, growers should take time now to ensure fertiliser applications are spot on.

A recent MAFF survey showed 70% of farmers had not calibrated spreaders correctly. Most operators check application rate, but ignore spread pattern, says John Crowe, of Independent Machinery Advisory and Technical Services.

"It is not enough to know the spreader has been calibrated for rate and the right amount has been applied. Knowing where fertiliser has gone is also vital."

Striping is the first sign of a problem, but by then spread pattern variation exceeds 20%. "That means at 200kg/ha, some of the crop is receiving 160kg/ha and other parts 240kg/ha. That can cause cereal yield losses worth £11/ha (£4.40/acre), and further quality losses, lodging and leaching risks," says Mr Crowe. Tray testing can reduce variation to 5%, he adds.

Fertiliser quality – bulk density, particle size and surface texture – has a marked effect on spread pattern and flow rate, he says. Machine condition is also important.

Operators must tray test spreaders each time new material is used. Trays, placed across the full bout width, collect fertiliser. These are then emptied into calibrated tubes to show evenness of spread. Machines should be adjusted and retested until a consistent pattern is achieved. This should be done with each type of fertiliser before the season starts, and periodically during it, particularly if non-SP5 material is used, says Mr Crowe.

Growers must also re-check each new batch of non-SP5 fertiliser, he advises. That may not mean a full tray test each time if the initial tray test is done in conjunction with a quality check.

For this, a "size check" box is used to check particle size. It sieves a small sample of fertiliser, so different size particles fall into separate chambers. A trace of the pattern is then drawn onto a clear plastic card. A record is also kept of correct spreader settings.

New batches can then be checked against that card. If the result is the same, the spread pattern should be identical to the original tray test.

Whichever material is used, spreader setting and condition must be maintained, warns Mr Crowe. Mid-season tray tests provide a quick and easy check.

Tractor lift arms must be level, and the top link adjusted to give the right amount of pitch where recommended.

Worn deflector plates cause problems, and tired moving parts like bearings also dramatically change spread pattern.

Tray checks are also useful on windy days. "People often ask what effect windspeed has. Test, and if the pattern is affected, stop," says Mr Crowe.

Spreader height is critical and can vary with tramline depth, soil condition and crop growth. A chain, cut to the right length and attached to the frame, is a good visual check.

Deflector plates must be kept clean, especially in damp weather, adds Mr Crowe. "Some materials, like sulphur products, form a film on the disc vanes, which can affect spread pattern."

Headland attachments should always be used to avoid polluting hedges and ditches, he points out. They also ensure the correct rate is applied to the edge of the crop, boosting yield.

&#8226 Details of training courses and calibration equipment are available from IMATS on 01948-663768.

Spot-on spreading…at a recent Mid-Kent Training Group meeting, farmer Brian Wrout (right)and tractor driver Andy Head found their Lely Supabowl was spreading SP5-rated nitrogen accurately over 24m.


&#8226 Denser material and larger particles spread further.

&#8226 Surface texture affects flow rate and spread pattern.

&#8226 Spread patterns vary widely, but are often overlooked.

&#8226 Tray test pattern at start of season and check each new batch of fertiliser.

&#8226 Check machine performance periodically for wear, height, and wind effects.

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