Easy on N until surplus tillers have been killed

27 February 1998

Easy on N until surplus tillers have been killed

By Andrew Blake

DONT grow cereals like grass, warn crop specialists. Management must be geared to producing the right number of ears at harvest, not a thick crop of leaf.

Their advice is to be firm and let thick wheats look sick before applying nitrogen. Many crops need to shed tillers for optimum yields to be achieved.

Careful tiller counts to guide management decisions are a must. Be ultra-cautious with top dressings unless soil nitrogen tests show few reserves, they advise.

"Wheat is not a biomass crop," warns John Blackman of CPB Twyford. Yield is not necessarily related to leaf production, he says.

Final ear population for optimum output in most varieties is 500-700/sq m, says Mr Blackman. "But some crops probably have 2000 tillers/sq m at the moment. Applying nitrogen now will just encourage them all to grow."

Best results come from relatively thin crops receiving plenty of sunshine in a fairly dry late April/early May, he maintains.

The main uncertainty now is how many tillers will succumb if colder weather returns next week. "We just dont know what the losses may be," says ADASs John Garstang.

Another unknown is what allowances should be made to offset potential frost damage to main shoots in the most forward crops. Rapid developers like Rialto could be particularly susceptible.

But in most instances crops are so well-tillered the argument is academic, suggests ADAS consultant Neil Watson who co-wrote the HGCA-funded "Wheat Growth Guide". "If we are not careful we could be producing silage crops.

"It was very noticeable last year that crops in the east which looked as though they would win farm competitions early on failed to deliver, and it wasnt just because of the drought." Poor use of sunshine by overthick crops was also to blame, he believes.

Depending on variety the lowest number of ears for maximum yield is about 450/sq m, says Mr Watson.

This season that is rare and many crops, especially of varieties like Brigadier, already have many more. However, varieties differ a lot in their ability to retain tillers, he notes. Once crops reach GS31 tiller numbers tend to be set.

At ADAS Boxworth early-Oct sown Consort has a green area index (GAI) of 1, equivalent to 30% ground cover, reports Alan Gay. Last year at the same time the GAI was only 0.1. "The dry matter is 0.9t/ha compared with only 0.1t/ha."

But not all wheats are as well grown, which highlights the need for individual assessment. "At ADAS Rosemaund the GAI is only 0.2. Last year it was 0.6."

Mr Gays key message is not to panic.

&#8226 Western barometer grower Steven Mackintosh reports Buster and Consort wheat at first node (GS31) on early land at Homme Farm, Ross-on-Wye. Drilled on Sept 8 the crop was sown at only 260 seeds/sq m. But good germination and the mild winter meant 99% of plants survived, some with up to eight tillers each.

The normal first top dressing of 40kg/ha (32 units/acre) was delayed until just before GS31 (stem extension), by which time the smallest tillers had become defunct, he explains.

"The crop is more manageable now," he says. A straw-strengthening 2litre/ha spray of chlormequat has also been reassuring. "Frost is now the biggest worry."


&#8226 Warm winter stimulation.

&#8226 Excessive tiller numbers.

&#8226 Losses unpredictable.

&#8226 500-700 ears/sq m optimum.

&#8226 Degree of self-regulation.

&#8226 Avoid nitrogen push.

Forward wheat at Ross-on-Wye recovered from flooding and delaying Nuntil GS31 killed excess tillers, says manager Steven Macintosh. All farmers are now being urged to check tiller counts before spreading.

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