Cutting down trees was a common way to clear land for agricultural production a century ago on the fringes of the Prairies.
When they were done, the pioneers dragged the trees into windrows or brush piles and burned them.
But a strange thing happened when they finally got around to sowing a crop, said Jerome Lickacz, a former Alberta Agriculture agronomist. The land produced higher yields on the spots where the brush was torched.
“Where the brush windrows were burned, they noticed the crop was always better and the alfalfa grew very well … but they didn’t understand why,” said Lickacz, who farms southwest of Edmonton.
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He said it’s fairly simple: ash from the trees improved the soil’s pH and injected a large dose of phosphorus into the soil.
Today’s farmers aren’t going to drag fallen trees onto their canola fields to improve soil fertility, but there is a modern alternative: applying wood waste from the forest industry.
“Rather than pushing trees into a pile and burning them, like you did when you developed the farmland, now you’re bringing ash in from an external source and putting it on the farmland,” said Lickacz, who acts as a liaison for forest companies, selling farmers on the idea of treating acidic soil with wood ash.
“From the farmer’s standpoint, it’s a good situation. They (can) vastly improve the productive quality of their soil at a very minimal cost.”
In Western Canada, 6.3 million acres have a soil pH level of six or less, which restricts the growth of alfalfa, a crop with low tolerance for acidic soil. The growth of a moderately sensitive crop such as barley can be reduced when soil pH is lower than 5.8.
Most of the acidic acres are in Alberta, primarily in the western and northern edges of the Prairies, Lickacz said in a 2002 article for Alberta Agriculture.
“Essentially you’re looking at the fringe areas, where you’ve got the interface between the forest and the prairie vegetation … what the farmers commonly call the grey-wooded soils or the luvosolic soils,” he said in a recent interview.
“Here in Alberta, we’re looking at west of Red Deer up to Drayton Valley … and the Peace River country.”
In the 1980s, the Alberta government subsidized the cost of trucking limestone from the eastern slopes of the Rocky Mountains to the agricultural regions of Alberta so farmers could apply lime to acidic soil.
The subsidy cost the province millions, so government officials asked Lickacz to look into alternatives for treating acidic soil.
Wood ash made sense because it was readily available from Alberta’s pulp mills, saw mills and fibre board plants.
In on-farm experiments near Edson, Alta., in the late 1990s and early 2000s, Lickacz evaluated the yield of an alfalfa and timothy stand after acidic soil was treated with either wood ash or lime or not treated at all.
The wood ash plots yielded 2,800 kilograms of forage per acre, far exceeding the check plots, which produced 1,800 kg per acre. The plots treated with lime yielded 2,400 kg per acre.
One of the experiments was done on a field owned by Ron Schlender, who noticed an immediate difference in hay land treated with wood ash.
“They applied it to about 95 acres,” he said.
“We had a couple of bumper crops, going from 80 to 120 bales up to 180 to 200 bales on the same land.”
The experiments proved the agronomic benefits of applying wood ash, but it’s uncertain how long the benefits last.
“What we found from our plot work is that there appears to be enough phosphorus coming out of the wood ash that a farmer could suspend phosphate fertilization,” Lickacz said.
“How long that (impact) would last, we don’t know.”
He said it’s difficult to compare one substance to another, but wood ash likely provides soil benefits for the same length of time as lime.
A 1970-93 trial that applied lime to plots in west-central Alberta showed consistently higher barley yields compared to the check plots.
“Our experience with using limestone…. (the benefits) last at least 20 years,” Lickacz said.
John Zylstra, land management specialist with Alberta Agriculture in Fairview, said the evidence shows that wood ash is an effective way to raise soil pH and add phosphorus to the soil.
However, the research on wood ash was done a decade ago and it’s hard to know how many producers adopted the practice.
He said applying wood ash to acidic soil makes economic sense if the agricultural land is sufficiently close to a pulp mill or other source of ash because the product is bulky, making it expensive to haul.
Less wood ash may be available now because the forest industry has become more efficient. As well, farmers are likely growing crops that tolerate acidic soil rather than applying wood ash or lime.
“By and large, they’re not really treating (the soil),” Zylstra said.
“Most people will grow red clover (instead of alfalfa). That’s a solution that doesn’t fix the soil problem, but it’s a solution.”
However, Zylstra said low pH soil becomes more acidic over time and farmers in Europe regularly apply lime to their fields, which means applying wood ash may eventually become a common practice on Canadian farms.
“I will venture a guess that if crop prices go higher, or stay high, it’s possible that the economics may allow this to happen.”
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Why are soils acidic?
•Soil acidity is a natural and ongoing process. Soil that developed under forest cover is normally acidic; if that soil develops under pine or spruce, it may be strongly acidic. Farming activities that contribute to soil acidity include use of manure and nitrogen and sulfur fertilizers. Naturally occurring causes include organic matter decay, leaching, organism respiration in soil and precipitation.
How much lime or ash is required to change soil pH?
•Typical rates of ash are three to four tonnes per acre. The amount of liming material is determined by the initial pH of the soil, amount of clay, organic matter in the soil and desired pH. Liming to pH 6.5 is recommended for alfalfa.
How is ash applied?
•Ash is a fine material and is applied with a lime spreader. Most fertilizer spreaders are not adapted for spreading ash because of a difference in rate of application. Ash should be uniformly mixed into the topsoil to achieve maximum benefit.
How should the land be managed after liming with ash?
•The neutralization reaction in the soil depends on time and moisture. As a result, an acid sensitive crop such as alfalfa should not be planted for at least one year after ash is applied.
Source: Jerome Lickacz, former Alberta Agriculture agronomist
Tissue tests are money well spent for growers who are unsure if their crop needs more nutrients, says John Heard, a soil fertility specialist with Manitoba Agriculture.
“If (it) looks like there’s some ailment, you should do a complete diagnostic evaluation, which generally includes a tissue test and a soil test,” he said.
Farmers Edge, an agriculture consulting firm, started conducting in-season tissue testing at its lab in Winnipeg this spring.
Marketing manager Brad Ewankiw said it is a tool that can help growers trouble-shoot problem areas in their crop.
“If they have a cereal crop and there are areas that are yellowing or doing something odd, they would be able to take some samples of the leaves and potentially identify the deficiency.”
The service is in its infancy, but Farmer’s Edge has already received tissue samples from across Western Canada for canola, corn, alfalfa and wheat, said lab operations manager Laura Cross.
The company charges $45 for a complete analysis of a tissue sample and says turnaround time is three days from sample submission.
Heard said Manitoba growers sometimes try to save money by sending a sample to the province’s Crop Diagnostic Centre for a free visual diagnosis.
However, he said the diagnosis can be uncertain and inexact because a visual inspection only tells so much.
“Yeah, it’s yellowing. Maybe it’s nitrogen, maybe it’s sulfur or maybe it’s something else,” he said. “People have to be willing to pay to get the answers sometime.”
Heard said a yellow or damaged plant doesn’t always indicate a lack of nutrients in the soil.
“Just the other day I took some tissue samples from a field and found out it was probably herbicide injury,” he said.
“But a soil test might say that there’s enough (nutrients) in the soil. (So) it’s not a problem where the plant needs to be supplemented, it’s a case where another type of injury has caused the symptoms to appear.”
He said testing is also beneficial because of growers’ tendency to assume yellow crops are nitrogen deficient.
“But in the last few years we’ve observed a lot more cereals and corn coming back with sulfur deficiencies.”
As well, said Ewankiw, a tissue test can provide information on what’s happening right now.
Heard cautioned that tissue tests can provide an incorrect diagnosis if plants are in extremely wet soil.
This year, crops in Manitoba and southeastern Saskatchewan are turning yellow because they cannot absorb nutrients in the soil. A tissue test might indicate a nutrient deficiency when, in fact, the soil has sufficient nitrogen.
“Don’t take a tissue test now because, guaranteed, things are going to be lacking or deficient,” Heard said.
