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Low, high or in the middle, soil pH affects your farm

Acidic or alkaline soils can have a big effect on soil nutrition, but while farmers with acidic soil 
can turn to lime, fixing alkaline soils may be more of a challenge

Alkaline soils are a common problem in Manitoba, but farmers may not have an easy fix.

Amir Farooq, crop specialist with Manitoba Agriculture and one of the speakers at a soil fertility update in Brandon Jan. 30-31, argued that high pH soils would need a prohibitively expensive amount of elemental sulphur to lower levels.

The province also has patches of low-pH acidic soil east of Brandon, through the Riding Mountain and Duck Mountain regions and in the eastern edge, according to Manitoba Agriculture.

For most of agricultural Manitoba however, pH sits neutral or climbs above 7.4. Alkaline soils are the norm in most of the Interlake, as well as much of the far southwest Red River Valley and areas around Dauphin.

Sometimes, for certain crops, acidic soils can be an advantage.

“Potato farmers, they like acidic soils,” Farooq said. “They like low-pH soils, like close to Carberry. There are some special crops like blueberries, they also need acidic soils.

“If you want to grow the crops like potatoes and special crops, try to find those fields that already have pH low,” he added.

Other provinces echo Farooq’s message. The Ontario Ministry of Agriculture, Food and Rural Affairs encourages farmers to choose already acidic land for blueberries, since soils with pH over seven tend to resist change.

“Any changes would be short lived and the pH would soon return to where it started,” their horticulture page states.

Free carbonates like calcium and magnesium also block efforts to lower pH, they add, since those elements tend to react with acidifying elements, cancelling them out.

Ontario’s sulphur guidelines estimate that it would take 312.26 pounds of elemental sulphur an acre to lower pH by one point on sandy soil, a number that goes up to 669.14 on sandy loam and 981.4 for loam soils.

That’s still lower than studies out of South Dakota State University in the early ’90s, which found that lowering pH from 7.8 to 6.6 took 4,000 pounds per acre of sulphur, and that it took double that, 8,000 pounds per acre, to jump further down to pH 5.7 in the first three inches of soil.

Farooq pointed to the South Dakota study during his talk Jan. 30.

Banding phosphorus and micronutrients may be a more economical way to handle alkaline soils, the Manitoba Agriculture employee said. Fertilizer bands are already acidic and could cross over the advantages of acidic soil in the area directly around the seed row.

Farooq doesn’t advise doing away with sulphur fertilizer on high-pH soils, despite the dim outlook for long-term pH changes. Crops like canola can often use a sulphur boost, he said.

“I think pH is very crucial to use all these nutrients wisely, so I think this is a message to farmers if they want to improve their soils and if they want to improve their nutrient efficiency, they should consider the pH level,” he said.

What’s the problem with high pH?

High pH may limit available phosphorus, according to both Farooq and Tom Jensen of the International Plant Nutrition Institute.

The same South Dakota study reported that available phosphorus rose from 27 parts per million to 52 as sulphur was added and pH dropped from 7.8 to 5.7.

“Theoretically, if you lowered pH, you could manage phosphorus better, but you can’t afford to put on that much elemental sulphur,” Jensen said. “It’s amazing how good of crops we grow on higher pH.”

High-pH soils may face phosphorus and nutrient issues, he said, but acidic soils may face toxicity issues.

Jensen tagged a six to seven pH as ideal for phosphorus availability. The nutrient tends to get tied up with iron and aluminum in more acidic soils and calcium as pH slides towards alkaline, the room heard.

Fungal-bacterial balance may also skew in favour of bacteria in high-pH soils. Mycorrhizal fungi are a known asset for certain crops to access phosphorus. Alkaline soils, however, are a less friendly environment for fungi as a whole, Jensen said, while bacteria thrive at higher pH.

Farmers may also want to balance salinity issues before dumping on the sulphur, Farooq said. The researcher pointed out that acidifying soil, while it encourages microbial activity and increases available phosphorus, may also increase salinity risk.

About the author


Alexis Stockford is a journalist and photographer with the Manitoba Co-operator. She previously reported with the Morden Times and was news editor of  campus newspaper, The Omega, at Thompson Rivers University in Kamloops, BC. She grew up on a mixed farm near Miami, Man.


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