8 August 1997

Cutting seed rates a risky business

TRIMMING seed rates for winter oilseed rape can be risky and the savings relatively small, says Mr Gillings. That view is reinforced by ADAS and Morley Research Centre.

"If conditions are perfect you can get away with 2-3lb/acre for conventional varieties. I have got people doing it. But I am loath to suggest the vast majority of growers are capable of getting that low, and in a dry season there is no way I would recommend it.

"The average conventional seed cost is about £16/acre. If you reduce the rate by half you are still only talking about saving £8/acre. You only need another 1cwt/acre of yield to pay for the full rate."

Standing power

ADASs John Garstang believes there may be a case for adjusting seed rate to cater for variety standing power, stiffer types permitting slight reductions to avoid tall thin weak plants. "But that is not good advice in pigeon areas."

It is sometimes forgotten that ADAS trials show thick autumn canopies give good weed suppression, he adds.

"The problem with reducing seed rates is that you just do not know what pigeons, slugs and the winter are going to do."

Experimental data from as far back as the 1970s indicates that seed rates of 7kg/ha for conventional varieties are not always necessary, says Ben Freer of Morley Research Centre.

Lower rate option

That is the background to new trials examining sowing rates ranging from 120 seeds a sq m to as low as 40/sq m in both Apex and composite hybrid Synergy.

Unfortunately, last seasons high seed rate plots failed to generate any more plants than the lower rate seedings. But at the low rates there was no significant yield difference between Apex and Synergy at 4.7t/ha (1.9t/acre) and 4.6t/ha (1.86t/acre), notes Mr Freer. "It confirms that you can get away with very low rates. But I am certain that cutting the Synergy rate below 3.5kg/ha would be dangerous."

"With standard conventional varieties seed cost is not a major concern. If it does become more of a factor, then maybe we will have to look more at precision sowing and better seed placement." &#42