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Low Soil pH Levels

Saturday, January 1, 2022
filed under: Fertility

Add this to the prospective list of problems to deal with in 2022: low soil pH levels.

field with low pH level — Photo credit: Don Lilleboe

        Extension agents across North Dakota report pH levels at an all-time low across parts of the state and into South Dakota and Montana as well. Low pH levels mean soil is more acidic and there could be deficiencies in the available supply of nitrogen and other essential nutrients, along with many other issues that impact crop production.
        It is an issue Ryan Buetow has been learning more and more about since he started as a cropping specialist at NDSU’s Dickinson Research Center in 2015. “This issue is taking up all my time these days,” Buetow says.
        In 2017, he recalls, there were several reports of low pH levels in area fields. He says these were not just small spots; in some cases, it was the entire field.
        FMC Retail Market Manager Bob Weigelt says it is something that has become important over the past decade to growers in North Dakota. “It really snuck up on us the past 10 years,” Weigelt says. “It surprised some of us industry people. The thought of having too low of pH levels was something we rarely thought about in the first 30 years of my career.”
Now, it’s being talked about in just about every conversation Weigelt has with growers, industry experts and researchers.
        The pH of a soil influences nutrient availability, toxicity, microbial populations, and activity of certain pesticides. Soils with a pH less than 7.0 referred to as acidic, while pH levels greater than 7.0 are considered basic or alkaline.
        Buetow explains that in North Dakota, pH levels have historically been greater than 7.0 for much of the state. Along the Missouri River and further west, levels trend lower. But he says as the state has gone to no-till, levels have slowly dropped.
        During the 2021 sunflower crop survey, he pulled soil samples. His findings show the low pH levels are widespread, from Divide County in the northwest corner of North Dakota, to Emmons County in the south central part of the state — and into Perkins and Corson counties in northwestern South Dakota.
        Buetow’s samples show the lowest pH levels occurring in western North Dakota — as low as 3.9 in Slope County and 4.3 in Hettinger County.
        Buetow says when the pH levels drop below 5.5, aluminum becomes more soluble and damages plants.
        “Aluminum stunts a plant’s roots, and it can cause some pretty rough yield loss — and, in some cases, complete stand loss, depending on the situation,” he explains. “Each crop is affected differently. And while I don't have any data on how sunflower is impacted specifically, I do have anecdotal evidence from farmers. You can see in the fields where the pH is different there is definitely a yield hit being taken by the ’flowers, even though they do grow in those acidic zones.”

        Herbicides are also affected by low pH levels. Brian Jenks is a weed scientist with NDSU’s North Central Research Station at Minot, N.D. He says many herbicides break down through microbial activity. Low pH can decrease microbial activity, which in turn can degrade the herbicide more slowly.
        “That could be a bad thing,” Jenks says. “In general, the effect of pH is going to depend on the specific herbicide. High pH could lead to crop injury (e.g., Spartan), and it can also lead to longer persistence of the herbicide. Lower pH can also lead to more carryover of the herbicide (e.g., Pursuit, Raptor/Beyond), depending on the chemistry. Lower pH can also decrease herbicide activity. There is some good and bad to both high pH and low pH.”
        Jenks says producers should take a look at the specifics of each herbicide and the effects it could have in soil with a low pH. It’s also important to note total rainfall in an area; some herbicides have restrictions based on soil pH and rainfall.
        “There are restrictions and issues that could affect what growers plant in the spring,” points out FMC’s Weigelt. “If the drought persists, it could affect what herbicides are used — and that could affect a grower’s crop rotation.”
        “Producers need to look at the herbicides they used last year, as well as at the rotation restrictions to crops they hope to plant and make sure there isn’t’ a restriction to growing that crop based on rainfall of pH,” Jenks adds. “Generally, the restrictions are more related to rainfall; but some do hinge on pH.”
        The key, Buetow says, might just be in the soil samples.
        “Ideally, farmers would have soil sampled this fall; but if they haven’t, they should do that before spring planting,” Buetow advises. “We really need to get more site specific with soil samples. We’ve seen varying pH levels in the same field, so it’s important to utilize zone samplings so you know exactly what you’re dealing with before you plant your 2022 crop.”
          Buetow and Jenks will present findings on weed control and acidic soil at the Diversity, Directions and Dollars Ag Forum in Dickinson, N.D., on January 11. Contact the Stark-Billings County Extension office at 701-456-7665 to learn more about the event and to register. — Jody Kerzman