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Thursday, 16 February 2012 10:51

Cultivar trials flawed here and abroad

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CROP VARIETY testing systems the world over are inherently misleading and New Zealand's are no exception, says a leading wheat breeder.

John Blackman, the man behind many top performing cultivars over the years, such as Equinox, Raffles and Robigus, believes trials should include plots grown to the breeder's prescription.

The problem with the standard treated versus untreated approach is that all varieties on a site get the same management, with nothing tuned to the cultivar.

"We need to rethink the way we trial varieties," he told Rural News.

Besides the issue of one-size-fits-all agronomy (same sowing date, seed rate, fertiliser, fungicides and pgrs) on trial plots, growing early and late varieties, and short and tall varieties side by side – or however the randomised plot design dictates – also causes problems.

Tall types are favoured because they get more light, and late types because they don't suffer the same amount of bird damage, he explains.

"Birds only need to take two grains per ear and that's a 4% yield difference. But when you look at the plots, most people wouldn't even notice two grains missing."

Rain late in the growing season can also skew results, again favouring later maturing types, as it did in the UK's 2011 harvest.

Surrounding crops seem to have an influence, boosting the result of the cultivar that's the same as the crop. "If you want a variety to yield the most in a trial, do the trial in a field of it."

Site selection is also key, and he's critical of the spread in New Zealand where he says there are too few with high yield potential.

"If it isn't high yielding, it's not relevant. The yield potential of wheat here is 18-20t/ha in the right season, so you need to work with farmers who are regularly achieving 15t/ha. It is crucial to take account of site and seasonal characteristics in interpreting variety performance," he stresses.

And where wheat trials are irrigated, managers need to resist the temptation to keep topping up the moisture, as do growers with irrigation.

"There's a tendency to keep the water topped right up because that's what the irrigation people tell you to do, and you do need to with potatoes and grass. But winter wheat?

"We don't really know, because no-one has done the work with these European winter varieties, but I don't believe you do... winter wheat needs to be stressed."

When it comes to interpreting trial results, too much emphasis goes on yield, without taking account of the factors behind that.

"As breeders we have to try to make sense of it all. If we just went on yield this year we'd be likely to pick a tall, late variety, just like they have in the UK... You need to be [in the trials] earlier to tell anything."

Blackman accepts there have to be some compromises to keep trial design and cost practical, but believes current systems are over-simplified, and the industry could do better.

However, after decades in the business, he's philosophical about the likelihood of change.

"You know my philosophy: breed good varieties which occasionally, by accident, get recommended."

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