22 August 1997

Good roots help OSR weather the winter

AIM for short, thick-stemmed well rooted plants to minimise the effects of winter kill and drought in oilseed rape, advises a Worcs-based seed supplier. For some varieties that may mean easing back on seed rates.

In striving for optimum plant populations much depends on sowing date, drill width and seed rate, says Brendan Paul of Perryfields.

"Rape needs good roots to withstand winter and possible spring drought. Root potential is fixed in the autumn by a combination of day length, temperature and, what is often forgotten, physical contact between the plants."

That applies to all varieties, he says. But growers of particularly vigorous types, like Licrown, should to take extra care to avoid producing mini-hedges of tall thin, weak-stemmed stands with poor root systems, he says.

Soil conditions clearly have a big influence on emergence and subsequent growth, Mr Paul admits. But choosing a narrow drill width and winding down the seed rate when sowing early could pay dividends.

Work by German breeder DSV shows the size of the root system is set as day length decreases after mid-October. "After that the plant switches its energy into producing foliage and flower buds. If the plants begin to touch in the rows this switch happens earlier before sufficient root has been established."

For a given sowing rate, the wider the drill width the denser the stand in the rows becomes. "If the row width is too wide, the plants in the row compete with each other, cannot grow large enough and are killed out by frost."

DSV experiments (see graph) show crops emerging at 100 plants/sq m in rows 8.5cm (3.3in) apart suffer only half the winter kill as those coming through at twice the row width.

Licrowns autumn vigour helps minimise weed competition and pigeon damage, he adds. "That means many growers could afford to pull the seed rate down to about 10% below the 5-7kg/ha they would normally use.

Target spring plant population is 70-90 plants/sq m. "Allowing for winter kill that means sowing about 120 seeds/sq m." Only raise seed rate when broadcasting or in poor seed-bed conditions.n

Drill rape too close down the row and autumn competition can restrict yield potential, says Brendan Paul of Perryfield Seeds.

WINTER KILL

&#8226 Autumn root growth vital.

&#8226 Competition between plants in row can be limiting.

&#8226 Narrow row width may help.

&#8226 Scope to trim seed rates for vigorous types.

&#8226 Ideal drill width 10-20cm (4-8in).