Acidic soil threatens southwest ND yields
DICKINSON, N.D.—Extra wet growing seasons and gravel- or sand-based soils have led to soil acidity, cutting crop yields and creating weed and herbicide problems in parts of southwest North Dakota, farmers and crop experts say.
Soil acidity was one of several topics covered Jan. 14 at a Diversity, Direction & Dollars agricultural forum in Dickinson.
"I think it's very concerning because it's affecting more than just our crops; it's affecting our whole system," said Ron Kessel, on a farmer panel. He said acidity is "leading to a reduction in productivity and when we reduce profitability."
Kessel of Hettinger, N.D., farms near Belfield, N.D., but he's also a branch manager/consultant for Helena Agri-Enterprises, a company based in Collierville, Tenn., near Memphis. The company has wholesale and retail operations in the lower 48 states.
Jon Wert, a New England, N.D., farmer, said extensive use of nitrogen over many years has contributed to the problem. The ammonium ion in nitrogen fertilizer has hydrogen in it and is released in the soil. Hydrogen is the indicator of an acid soil.
The "pH" level (stands for 'potential of hydrogen") scale goes from 0 to 14. The midpoint of 7 pH is neutral. Lower pH numbers are acidic and high numbers are basic. (Bases that dissolve in water are called alkali.) "We've had issues out in the field, we just didn't recognize that it was a pH issue," Wert said.
Waking to issues
When the soil is neutral at 7 pH, fertilizer is 100% efficient. But when acidity "gets down into the 4s, we are wasting 71% of every fertilizer dollar we spend," Wert said. "Those nutrients—NPK (nitrogen, phosphorus and potassium) become less available in an acidic environment," Wert said. Some of the soils had been in pH 6 ranges or "close to neutral", and now are in the 5 pH or even 4 pH, especially in the past four years, Wert said.
Ken Froelich, North Dakota State University Extension agent for Stark and Billings counties, said the problem reaches up into Dunn County and down to the South Dakota border and perhaps beyond. Herbicides are broken down in the soil by fungi and microorganisms. Increased acidity prevents that breakdown, creating herbicide carryover problems into subsequent crops..
Kessel explained that "sandy gravels tend to have a lower pH," he said, meaning they are becoming acidic," Kessel said. "A field can have an area of heavy clay or silt where it isn't acidic, and another gravelly area that is."
Acidity is a natural process, he said, and soils naturally acidify with time. When you add human activity into the system, "we change things and alter things. By adding nitrogen-type fertilizers, we accelerate the acidification process."
Extra rainfall in the system, like the wet 2019 crop year brings on the symptoms, Kessel said.
Tools to address
Once a problem has been verified, farmers can counter-move against it using variety selection, crop rotation, different fertilizers that are
"What I"m finding with our clients, they say some of those (newly acidic) areas used to be our most productive fields, or productive parts of fields," Kessel said. "They've seen that production slip. It's still OK, but how much more it could be if we addressed the issue of acidity."
Oats are more tolerant to higher acidity. Barley and durum wheat are more sensitive. Some varieties are more sensitive.
A common counter-move is applying lime. That's available as a byproduct of the Sidney Sugars Inc. beet sugar processing plant. Other sources include a municipal water treatment plant at Dickinson as well as some pelletized lime from Iowa.
"Right now, there's enough lime to address the issue," Kessel said. "It's more of a cost factor, and what the budget can afford." Wert said soil tests call for three tons of lime.
"In our farm, we're deep banding our anhydrous (ammonia nitrogen fertilizer) at the 2- to 4-inch zone, which is where our greatest acidity is," Wert said. "Guys that are top-dressing urea, their 0- to 2-inch area is where their acidity is the worst."
A lime application is about $100 an acre, Wert said.
The budget differs by producer. Kessel often advises clients to take the lime expense "out of the nitrogen budget." He may advise putting $12 per acre to $50 per acre into lime. "Long term, it'll give you a better return on your investment," he said.
Yield per acre is one thing, but the acidity change also affects how weeds survive and how long persist in the soil.
"As we find this acidity, we also see other symptoms that show up," Kessel said. "Weed populations will shift. Certain weeds will thrive more in acidic conditions compared to other weeds."
Farmers also rely on crop competition to help with weed control. "Once we get reduced crop competition, Mother Nature is going to cover that ground with some sort of vegetation. We open it up for weeds to come in." Plants stressed from acidic soils also can become more susceptible to disease pressure.