11 July 1997


A NEW trials layout will be adopted from this autumn by NIAB for oilseed rape varieties after criticism that the old system favoured composite types.

The hope is that yield results will more accurately reflect field conditions, says Adrian Pickett, head of combinable trials.

At present, composite varieties are planted among conventional varieties in NIAB trials. Unlike composites, all plants in a conventional stand produce pollen. As a result, pollen levels are higher than would be the case for a composite variety grown in the field. That aids seed set, artificially boosting yield, especially in cool, damp seasons, critics argue.

"We have had to ask whether our trialing system is a fair test of what is an unnatural reproductive system," says Mr Pickett. "But when you need to collect comparative data, it is difficult to change."

As a compromise, composite varieties will now be planted at least 12m away from conventional ones. Hybrid seed rates are also being reduced to commercial levels to mirror farm practice. They had been kept higher to try to eliminate edge effects in the plots.n

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