4 August 2000



HEAVY self-propelled forage harvesters and silage carting tractors and trailers could be costing up to 15% yield loss in silage fields.

Speaking at Mooreparks open day, Teagascs Dermot Forristal explained that a three-year study compared typical contractors silaging equipment with low ground pressure kit at two sites.

The contractors equipment used tractors of 6t, a harvester of 11-13t, and trailers which could weigh up to 18t when loaded.

"Just 20 years ago, a trailer full of silage would have weighed the same as an empty trailer today at 5t. The tyres on it may look big, but the pressure they are filled to at 50 psi, indicates the pressure they exert on the ground."

By the end of the study, yields were 15% lower where contractors equipment had been used compared with low ground pressure equipment on a wet site at Kilmaley, Co Clare. A drier site, where they expected little or no yield loss, also suffered a severe yield penalty at 8%. Thats without including headlands in the yield estimates and over three dry years, he said.

Buying the equivalent in lost silage at £56/t would have cost £50/ha (£20/acre) and £27/ha (£11/acre), respectively. However, reducing compaction would mean cutting tyre pressures by over half to 15psi (1 bar).

"That requires a huge increase in tyre size. In practice its difficult to achieve that and it would increase costs for contractors."

Although the required tyres are not currently available, he estimates the additional capital investment at £30,000-£40,000. "But using them for 2000ha a year, over a number of years means they would cost £7-£10/ha extra. Then you only need a yield increase of 2% to pay for them," said Mr Forristal.

"The benefit is there; the challenge is convincing contractors. Every one of his customers must demand it and be prepared to pay the extra."

The contractor must see a benefit to him, and in a wetter year it could allow silage making to continue in poorer conditions, he added. &#42

Conventional tyres on heavy silage making kit could be costing up to £50/ha (£20/acre) in grass yield losses, says Dermot Forristal.


&#8226 Modern silaging kit heavy.

&#8226 Grass yield reduced.

&#8226 Must convince contractors.

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