22 June 2002



ARC trials on plant spacing and establishment face a stiff test, as Gilly Johnson found out

IF YOURE drilling wheat at miserly or even exceptionally low seed rates, then each seed counts. So is a conventional drill the right tool in this situation? Would it be better to switch to accurate, precision placement? Should the seed be broadcast randomly?

As yet, no-one has the answers. But they will, thanks to a new HGCA-funded research project, run by the Arable Research Centres. The project is now approaching the end of the first season of a three-and-a-half year programme.

Under scrutiny on large block plots on a brash land site up in the Lincs Wolds is precision drilling of seed, broadcasting and harrowing down, and conventional drills run at a very slow speed. The idea with the last technique is to see if this improves placing precision.

"Were not trying to compare precision drilling with broadcasting or conventional drilling. Rather, were looking at how these systems produce different plant spacings and how we can manipulate this," explains the ARCs Dave Robinson.

As a yardstick, a block of wheat drilled with a conventional drill at 200 seeds/sq m, and driven at a normal speed of about 8km/hour shows some gaps and bunching. "These drills dont deliver seed at a constant rate down the coulter. And as the speed goes up, the accuracy drops – coulters bounce in and out of the soil surface and this affects the metering system. You tend to see a run of seeds, then a little gap."

Halving the forward speed to 4.7km/hour did give a more even plant population but a few gaps were apparent; at the end of the season, the plot will be assessed to identify if the visual effect comes through to yield at both 100 and 200 seeds/sq m seed rates. "However the idea of driving so slowly will not appeal if you need to cover large acreages."

So far, the big surprise has been the 100 seeds/sq m broadcast/harrow in block; the crop canopy looks even and well randomised, bar a few tufts where the wheelings made depressions into which groups of seeds rolled. "It must be the lowest cost system," says Mr Robinson. "But most people would consider it desperation tactics, done as a last resort."

The seedbed was in good condition; the crop went in on 22 September and seed was covered over well by the shallow harrow, then rolled. More alarming is the broadcast plot where seed rate is just 50 seeds/sq m and plants are very sparse; but this shows the extreme.

The precision drill used was an Accord drill, based on the companys sugar beet drill but adapted for cereals. Each seed is individually placed in wider 15cm rows, with 4cm between each seed within the row. "Having seed in wider rows, with a bare gap between, does pose a problem if youre trying to assess green area index," says Mr Robinson. "Weed competition could also be a problem but air down the rows could reduce disease pressure and increase grain bushel weights."

Another block involves precision drilling using narrow rows, and lower seed rate at 100 seeds/sq m. The canopy appears more even.

The trial aims to unravel how best to control the spatial planting of the seed; the next step would be to identify how to make each individual plant perform better within that canopy.