5 June 1998

Dense wheat canopies wont be high yielders

By Andrew Blake

WHEAT yields are likely to be no better than average this year, following a season of mistimed nitrogen dressings, caused by bad weather and over eager application alike.

Too many growers applied nitrogen too early, despite advice not to, notes a leading breeder. Many who waited for the optimum timing then hit delays as wet weather struck.

But growers with thinner crop stands are set for the best yields, claims CPB Twyford technical director John Blackman.

Early applications

Early applications have produced flag leaves which are too large and over-dense canopies. The optimum ratio of green leaf to ground area needed to intercept sunlight is about four to five at this growth stage, he explains. "The index on some crops this year is 12 and even more. That is completely over the top."

Good autumn establishment and the mild winter are partly to blame. But the main reason is growers eagerness to apply nitrogen too soon, he maintains. As a result lodging is likely to be a particular problem, especially as many growers missed critical growth regulator timings.

Crops with over-thick canopies are inefficient and waste resources, adds Mr Blackman. "All the lower leaves are senescing and using energy but not contributing to yield." The aim, particularly on erect varieties like Equinox, should be to keep flag leaves small and upright to allow maximum light penetration into the crop, he explains.

Bets on… Cambs grower Oliver Walston reckons his relatively lush crop of Equinox after beans should deliver 9.3t/ha (3.8t/acre), but a later sown, thinner stand after sugar beet will give just 8.3t/ha (3.4t/acre). John Blackman of breeder CPB Twyford believes excess leaf in the thick crop means just the opposite.