21 January 2000

Uneven spread pattern costing growers dear

UNEVEN spread of fertiliser under field conditions could be costing growers dear, even those with pneumatic spreaders, according to recent work at Silsoe Research Institute.

Crosswinds of just 6mph (10kph) can cause up to 30% variation in spread from a 24m spinning disc machine, depending on product quality. With a pneumatic spreader that is cut to just over 20%. But yield losses can still be substantial, says Hydros Jim Lewis.

"Growers lose 4-5t/ha of potatoes when variability of spread rises from 10 to 20%," he stresses. Wheat yield losses are less significant, at 0.12t/ha (1 cwt/acre) for a similar increase in spread variation with ammonium nitrate. But that is still worth £9/ha (£3.60/acre) and would be barely visible as striping.

"On top of that theres the quality aspect," he adds. Hagberg on milling wheat fell from 280 where spread patterns were acceptable to 193 at 20% variation. Specific weights were also lower.

Quality of the product is the key to cutting variability, maintains Mr Lewis. That is echoed by Silsoes Paul Miller, though spreader type does have an influence, he says.

"Spreading performance is a function of the material – the difference between a materials spread characteristics is greater than the difference between machines. The coefficient of variation for poorer materials is reduced with a pneumatic spreader, but it cannot cut the variation to the level achieved with better quality products," he warns.

Whatever type of spreader growers use, they should spend longer setting the machine up, believes Prof Miller. With SP5 rated material that may be done on the farm, provided growers re-calibrate for different batches of product. But for low grade materials spreaders should be professionally set up for that material, he says.

The work at Silsoe was all based on 24m tramlines. As tramline width is reduced product quality becomes less important, and at 12m growers could probably get away with using an SP3 rated material, he says. &#42