Scholar slams stubble burning as bad for soil

TIM CRONSHAW
Last updated 06:39 20/12/2013
Burning stubble in Canterbury.
Fairfax NZ

BURN-OFF: Canterbury farmers use stubble burning to clear straw left over from harvested crops, reduce insect pests and disease and provide a better bed for small seed crops.

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A Nuffield scholar visiting Canterbury, who would never burn crop stubble on his farm, has criticised the worldwide practice.

Arable farmer Tom Sewell, who grows crops on a 400-hectare farm in southeast England, was one of two scholarship holders studying the long-term benefits of no-tillage in New Zealand.

He left for Australia a week ago convinced farmers could avoid stubble burning, banned in his home country.

"There are loads of problems with it. In the UK it would be a [non-runner] in public relations and would be a shot in the foot. The public perception is it's bad for the environment, creating carbon dioxide and it's burning a valuable carbon source for the soil and losing organic carbon."

Sewell said UK farmers would produce as much straw as Mid Canterbury and it broke down in the soil within four to six weeks.

The farmer visited stubble-burning demonstration plots at the Foundation for Arable Research's (FAR) field day at Chertsey two weeks ago. He is cautious of FAR's review for Environment Canterbury which found stubble burning was valued by some farmers as a rapid, economic and relatively benign way of dealing with crop residue.

Sewell said burning was bad for the soil as it destroyed residue used to feed worms and build organic matter.

No tillage was a better solution and provided better crop establishment and higher crop yields, he said.

In the review, stubble burning was supported for managing crop rotations in Canterbury and valued particularly for cereal stubble burning as a rotational tool. Stubble burning is little used in Australia and no longer carried out in the US or UK, however, New Zealand wheat crops produced greater yields and more residue compared to Australia and more seed crops are grown.

Removing much of the wheat residue makes establishing grass, vegetable and clover seed crops - needing precise planting and prone to failure - easier and enables better control of weeds and pests such as slugs with fewer agrichemicals and pesticides.

FAR chief executive Nick Pyke said there were many issues to consider when deciding whether or not to use rotational stubble burning, as the expert panel writing the report found when it considered international scientific literature.

"On balance, and taking account of New Zealand conditions, the literature identified the use of stubble burning as a strategic option for residue management for some parts of the crop rotation in some seasons, especially when used to enable minimum cultivation approaches."

Sewell said UK farmers did not have the small seed crops planted here, but options such as cross slot drills pushed straw aside to get seed into the ground.

"I certainly won't burn any stubble. It's far too valuable to burn and I won't bale anything at all. My stubbles are returned to the soil and we can yield 12 tonnes to the hectare for milling wheat then place canola straight after that."

At his farm, between Maidstone and Tunbridge Wells, wheat is followed in a rotation by canola, known as oilseed rape, wheat again and spring beans. A bio-mulch product is sprayed on the stubble to help it break down after harvesting.

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Sewell has avoided phosphorus, potassium or lime on his soils and not ploughed for about 18 years, but has used shallow surface cultivation and uses nitrogen and other fertilisers for trace elements.

A horsch tine drill to put seeds in the ground will be replaced next year by a seeder being built in the UK with cross slot openers manufactured from New Zealand.

In New Zealand, Sewell visited Dr John Baker, a soil scientist and founder of the Feilding-headquartered cross slot drill company Baker No- Tillage Ltd.

Baker said retaining crop residue with no-tillage was a superior method than intensive ploughing with or without burning as any form of tillage was detrimental to soil quality.

Some UK farmers are trying to have stubble burning returned to control pests.

Sewell said this would be a "political own-goal" for farmers and they were growing wheat and canola rotations too closely and needed to diversify break crops.

He was impressed by the FAR field day, particularly with the plot selection for establishing wheat which he believed showed little gains for cultivation.

- The Press

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