Given the high cost of fertilizer, burning straw is a bit like setting part of your paycheque on fire.
John Heard, a soil fertility specialist with Manitoba Agriculture, says a significant amount of nutrients in crop residues such as straw can be returned to the soil.
If an average wheat crop leaves a tonne of straw per acre on the field, the economic value of that straw given the cost of fertilizer could range from $20 to $30, he added.
An experiment that Heard conducted in 2000 found burning straw destroys 98 to 100 percent of the nitrogen, along with 70 to 90 percent of the sulfur and 20 to 40 percent of the phosphorus and potassium.
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While commercial fertilizer offers an immediate benefit to growing plants, straw left over after threshing offers significant economic and soil health benefits over the long term.
“It’s like an RRSP versus a current account,” he said.
“Straw takes a major detour by going first into microbial biomass, then into organic matter and then it is metered out over time.”
As well, he said studies have shown that burning straw won’t rid fields of residual fusarium innoculum or weed seeds.
Straw is also a good indicator of fertility management. The higher nitrogen content of straw on fields where adequate nitrogen has been supplied causes it to break down much quicker than where a farmer tried to cut corners.
“If it has sufficient nitrogen in it, the microbes merrily chug away and decompose that straw,” Heard said.
“When it has low nitrogen content, in order to break down, the straw needs to borrow nitrogen from the soil. Sometimes that comes at the expense of the crop that is trying to grow at the same time.”
Although a number of straw processing plants in Manitoba have shut down, fibre markets for flax straw still exist, he said. Flax is said to have a similar heating value as soft coal and is commonly used as fuel for biomass heating systems.
“I expect that if a fellow has flax straw and it’s clean, he’ll have been contacted already by some of these buyers.”
Scott Day, a diversification specialist with Manitoba Agriculture, said a drought in parts of the United States has resulted in higher than usual demand for straw, which local baling operations are working hard to supply.
“Custom balers in our area have been delivering hay into Kentucky. The livestock there were completely out of feed,” Day said.
“These people had never bought feed before.”
A firm market price for straw has never existed in southwestern Manitoba, so the U.S. drought cannot be said to have boosted prices.
“People just drop it and get paid $5 to $10 a tonne and then somebody else makes money on it,” said Day, adding that the cost of shipping a bulk, low-value commodity is considerable.
Two years ago, Day sold winter wheat straw that was trucked 2,500 kilometres to Pennsylvania to be mixed into dairy rations.
“The desperation for straw must have been extreme,” he said.
“Most farmers don’t want to sell their straw because it’s good for the soil and has nutrients and so on. And we’ve learned how to deal with large straw volumes as far as seeding equipment. It’s not a big issue anymore.”
Manitoba’s restrictions on controlled burning, which are adjusted to apply to different areas of the province based on favourable smoke dispersion conditions, will be in effect until Nov. 15.
To find out when and where burning is authorized, farmers can call 800-265-1233 or visit the government website.
Authorization will be given daily by 11 a.m., which will allow farmers to light fire-guarded, fully supervised fires only within the times identified, and in areas where the smoke will not cause a hazard to human health or highway safety.
Night burning of crop residue, rights-of-way, ditches, native pastures and waste areas is banned year round.
