5 September 1997

TRIMSEED RATE SAFELY

Pressure to trim seed rates for winter wheat could be greater than ever this autumn as growers strive to economise in the face of low prices. Andrew Blake assesses the scope to cut back on seed inputs

BE BRAVE and you could be pleasantly surprised – provided you pick the right variety. So says John Spink, a research consultant at ADAS Rosemaund and leader of an HGCA-funded joint project with Nottingham University which aims to produce new sowing rate guidelines.

Many growers already sow by thousand grain weight, aiming to achieve about 275 plants a sq m in the spring. "But we know that for some varieties you only need 100 for optimum yield," says Mr Spink.

By adjusting rates more closely to variety and drilling date the industry could save £33m a year, he estimates.

Such fine-tuning should bring extra benefits, not least improved grain quality and less disease and lodging. Apart from a slight adjustment to spring weed control, crop management needs will stay much the same, he maintains.

Proof of the potential is already emerging in Rosemaund trials. They show that for some varieties rates as low as 20 seeds a sq m, about 10kg/ha (8lb/acre), can produce surprisingly good stands – even in a tricky season. But for others the same tactics are disastrous.

Wheat varieties fall into four main categories, explains Mr Spink. "Even in the UK there is a large variation in development and tillering capacity." Some, like Spark, tiller well and hang onto their tillers. Others, like Haven, tiller well but then tend to lose them.

Some, like Cadenza, (contrary to the report in Arable, July 18) produce few tillers and struggle to retain them. Others, like Soissons, are equally shy but tend to keep what they produce.

This means that in theory to achieve the same optimum 500 ear-bearing shoots for crops sown in mid-September the sowing rate for Soissons needs to be nearly two-and-a-half times that for Spark.

This season Haven, a free-tillerer, drilled in late September at only 40% of the standard recommended 375 seeds a sq m, looked much the same just before harvest as when sown at the normal rate. "And that was after far from ideal conditions for establishment," he stresses.

Even Haven plots drilled as low as 40 seeds a sq m leaving only 35 plants in the spring gave good ear counts. "Many commercial growers would probably have redrilled," comments Mr Spink.

Equally the experiments highlight the danger of being too mean with shy-tillering types like Cadenza or Soissons.

"Many growers get it reasonably right. But there is a massive degree of insurance in arriving at rates."

Geographical factors clearly play a part, he admits. "People in the north tend to sow at higher rates because the crop has a much shorter window for development."

Drilling date must also be taken into account. "Mid-September used to be seen as early 10 years ago." Now with set-aside wheat gets sown in August which greatly enhances tillering ability.

"Growers like to see a good thick crop in the spring. But that doesnt always contribute to high yield. You dont necessarily get a lower yield but you tend to get larger numbers of smaller grains which may influence specific weight and quality."

ADVICE FOR THIS AUTUMN

SO WHAT should the strategy be this season? Check the variety, note the drilling date and assess the seed-bed, advises Mr Spink.

Caution remains the watchword as this is only the first year of the trials, he urges. "But as long as you know have a good-tillering variety and you drill early I think there are some quite big savings to be made.

"With varieties like Consort, Brigadier, Spark and perhaps Drake, Raleigh and Haven, if you drill early, say mid-September, there should be quite a lot of potential to reduce rates." For a grower normally sowing 400 seeds a sq m it could involve a 50% cut, he suggests.

"The crops wont look so pretty through the autumn and spring. But come ear emergence you will be hard pushed to tell the difference with those sown later at more normal rates."

Trials suggest there is probably less room for manoeuvre with Riband, Rialto and Charger. "I would be very cautious with Caxton and Soissons," he adds. It is also unwise to sow Soissons before October because it can become winter-proud and prone to frost damage, he notes.

"As you delay drilling you certainly need to increase rates fairly rapidly. By mid-November you need to be up to 400 seeds a sq m for most mainstream varieties."

The standard figure for over-winter survival built into current sowing recommendations is 70%. Clearly if seed-beds are poor that figure may be lower and rates will need increasing to account for expected losses. "The person best placed to assess whether that is required is the drill operator," says Mr Spink. Some drills now permit on-the-move adjustment to cater for this, he notes.

"The same ideas apply to growers still working in stones/acre. People drilling at 16 stones/acre could be sowing about 640 seeds a sq m. Dropping that to 12 stones/acre using bought in seed could save £12/acre without much risk of yield loss in specific varieties."

Although the trials are still at an early stage growers should at least be prepared to try a couple of drill passes at a lower rate for comparison, he suggests. "There could even be a yield benefit on some soil types particularly in a drought year."n

W WHEAT SEED RATES

&#8226 Ample scope to trim safely.

lGood potential with early sowings.

&#8226 Use high tillering varieties.

&#8226 Take account of seed-beds.

From the left: Spark at 320, Haven at 160 and Spark again at just 80 seeds/sq m – all late-September-sown. The latter tended to stay greener longer, but otherwise it is hard to see the difference, says John Spink

of ADAS Rosemaund. "The Haven is fine at only 40% of what people normally use."

REDUCED RATE SPIN-OFFS

&#8226 Financial savings.

&#8226 Less lodging and disease.

&#8226 Better grain quality.

&#8226 More weed competition?

Big ears and larger flag leaves help compensate for thinner stands. This late September-sown crop of Rialto was drilled at only 80 seeds/sq m.