30 June 2000

August drilling pays

By Peter Grimshaw

DRILLING first wheats in August may be pushing the agronomic boundaries, but it can pay off, provided crop management is spot on and only the slowest developing varieties are used, says UAP technical director Chris Bean.

The goal is to develop a much more open canopy, says UAP southwest regional technical adviser Peter Gould. He believes many growers have been wasting both expense and potential yield on over-thick stands of cereals.

The good news for growers is that both the main management changes needed for a more open crop canopy save input costs.

The first step is a lower seed rate. In Wiltshire that probably means as low as 100/sq m. "But we still arent sure if that is OK, and maybe its fractionally low. Very little research has been done on tiller numbers on gutless soils like this, which lose their nitrogen rapidly, especially in a wet winter," says Mr Gould.

Seed rate must be appropriate to the soil type, the drilling date and the variety, he stresses. "Weve still got a lot to learn about how different varieties tiller, and how they hold onto their tillers."

The next major control lever is N, both amount and timing. "Nitrogen is the best growth regulator there is. We look very carefully at apical growth stages. The critical stage is terminal spikelet, between GS31 and GS32, which sets the timing for the main dose of N."

That timing varies from variety to variety, with, for example, Malacca as much a fortnight ahead of Claire. At this stage, the crop should ideally have 1000 tillers/sq m.

It is also at this stage that the success of fungicide treatments will be put to the test. "Its imperative to keep leaves two and three green for as long as possible," says Mr Gould.

He thinks the importance of the flag leaf as the power house of yield may have been overstated. "Its true that more than 50% of yield comes from the flag leaf in a dense crop. In an open crop, its likely to be nearer 30%, with the second leaf providing 20% and the third around 12%. Thats why, in managing an open canopy, its critical to time first fungicides to maintain the third leaf green for longer."

That even applies to Claire, a variety favoured for early drilling because of its slow development. "Even though it is Septoria resistant, it still needs a good fungicide programme if it is sown early." That is clearly seen in the Wiltshire trials, where untreated plots had suffered severe lower leaf loss.

There may be fewer ears/m with the open canopy approach, but they will probably be longer, with more grains set. "There are likely to be 60 or so grain sites/ear, compared with 40 or so under conventional management."

Mr Gould admits that the open canopy system may make little difference to yield in a normal year, although it should always save on input costs. "And in years when light intensities are low, we see a yield improvement of 1-1.5t/ha, compared with high-input crops."

Left:Choose the right variety and use the best agronomic advice and early drilling can pay, says UAPs Chris Bean. Inset:Thick crops are not the route to top yields, stresses UAPs Peter Gould.