Soil acidity a concern for Palouse farmers

Washington State University Farmers Network outreach coordinator Carol McFarland says soil acidity is a concern for farmers on the Palouse.

Declining pH levels is a growing concern for farmers and soil experts on the Palouse and in the inland northwest, said Carol McFarland, Washington State University Farmers Network outreach coordinator.

McFarland said acidic soil levels affect nutrient availability, soil biology and the effectiveness of herbicides. All three of which lead to a reduction in crop yield.

“Soil pH is known as the master variable,” McFarland said. “It literally affects everything else that happens chemically in the soil.”

The pH scale ranges from zero to 14. A pH of 7 is neutral, less than 7 is acidic and greater than 7 is basic. For agricultural soils, a pH below 5 is very low.

Climate is the driver of natural soil acidification. The pH of rain is 5.6.

Land management decisions, such as the commonly used deployment of ammonium-based fertilizers, also lower soil pH levels, McFarland said.

“Soil acidity itself is not a new challenge in the world, but here on the Palouse, it is because our soils have been historically in the neutral,” she said.

Tabitha Brown, of the American Farmland Trust, said in a 2016 WSU Extension video about soil pH that native Palouse soil pH was 6.5 to 7.

In the 1960s through the 1980s, pH levels declined because of an increased use of ammonium-based fertilizers, Brown said.

The levels range across the Palouse landscape. Even in the same field, Brown said the pH could be in the low 5s and low 7s.

Farmers can take some measures to mitigate soil acidity, such as applying lime to their fields. McFarland said this is a common practice in the Midwest, but limestone is not as accessible on the Palouse, and therefore, can be very expensive.

She said WSU has been working on research using other options like industrial byproducts that are more available and cheaper.

McFarland said farmers are becoming more aware of the problem and some are making fertility management changes to try to slow acidification.

She said many farmers are grappling with how to address pH levels on their land and balancing benefits and costs.

“They really need to see some sort of yield benefit if they are going to be able to justify the financial expense in a lot of cases, and I think that part gets a little tricky,” McFarland said.

She said it is crucial for landlords to care about the soil health of their land because it strongly affects the long-term productivity of that land. McFarland said it is common for farmers to own and rent farmland.

“You have people wanting to preserve the farm legacy and be good stewards of the land that they own, but it’s a lot harder when that carries over to something that they don’t own,” she said.

Garrett Cabeza can be reached at (208) 883-4631, or by email to

Recommended for you