16 August 2002

SAC urges caution with seed rates in the north

Reduced seed rates are all

the rage, but some growers

in the north and Scotland say

the trend has gone too far.

Andrew Swallow reports

START with the plant count you want in the spring and then work back, allowing for every possible loss in the worst part of the field to find the seed rate you should be using, advises SAC Scottish Agronomys Allen Scobie.

Growers have little to fear from using higher seed rates in the north, but much to lose if rates fall too low, he says. "Farmers have got to think about risk management. What you stand to lose by being below the critical seed rate is far more than the expense of a little extra seed or pgr."

In the north and Scotland, yields from above "optimum" seed rates plateau rather than fall away as may be the case further south, he says. Sowing a little extra seed is simply an insurance against falling off the edge of that plateau.

"With grain and seed prices much lower than they were the cost of that insurance is very low, especially when you save your own seed."

Arguments that thicker stands create a micro-climate more conducive to disease have been over-stated, he believes. In thinner crops, fungicides are arguably more important because lower leaves need to be kept green to reach full yield potential.

Thin crops also cause combining difficulties with secondary and tertiary tillers still growing when main stems are ripe. Even after drying grains from immature tillers spoil a sample.

"The problem is thin crops never ripen. Youll find it is difficult to remove the flowering husks off the grain and they reduce the bushel weight."

Mr Scobie acknowledges pgr costs may be higher if the plant stand achieved is above the minimum required for maximum yield. But pgrs are cheap relative to the risk of losing yield if too thin a crop results.

"You can put together a comprehensive pgr programme for under £10/ha."

Above minimum plant populations tiller numbers/plant tend to fall to compensate, he says. The result is that higher seed rates end up with similar ear counts, without the risk of too thin a stand going into winter.

At the other end of the scale, a low seed rate tends to result in lower % establishment, exacerbating the problem of a too low plant count (see table).

Similarly, too thin crop stands tend to be more prone to frost heave and allow more weeds to establish.

Mr Scobie stresses he does not question the original data behind the trend to reduce seed rates, merely the interpretation of it, especially for growers in the north.

"There is nothing wrong with the data, but farmers need the right message. Seed rates should be at a level that in the worst case scenario the plant stand doesnt drop too low.

"You have to accept that some areas may be thicker than optimum to ensure the poorest areas do not drop below that optimum. A higher seed rate has never penalised us on yield, but recently there have been incidences where too low a seed rate has," he says. &#42