POMEROY, Wash. — Roughly 90% of the soil in the Pacific Northwest does not have an optimum pH level, longtime Washington State University researcher Paul Carter says.

Yields might be going up, he said, but not at the same rate they would with healthier soil.

He estimates there would be a 5% to 30% yield increase if the soil pH were corrected. Soil pH is a measure of its acidity.

“I like to think of it as a silent thief in the night, running off with your nutrients, and you don’t even know it,” he said.

Carter retired in January from WSU’s Columbia County Extension, where he was director and regional specialist.

He has continued to work as a soil consultant. His other projects include building or rehabilitating the small combines and other equipment used on research plots.

He didn’t want research on acidic soils to stall, so he’s continued to work one or two days per week on that project.

Investing in agricultural limestone is the only sure-fire answer to rectify soil pH problems, Carter said. He hopes to reach a point that growers apply a maintenance application of lime every five to 10 years.

A pH level of 7 is considered neutral between acidic and alkaline, or basic. Most soil around the region used to have a pH of 6.5 to 7. Now the pH in a lot of fields has dropped, making the soil acidic.

“We have farmed these soils for the last 100, in some places almost 150 years now,” Carter said. “That alone tends to cause the pH to drop.”

As plants pick up nutrients, they give off hydrogen ions, lowering the pH of the soil. Use of nitrogen fertilizers has exacerbated the situation, Carter said. Applying nitrogen to the soil adds more hydrogen ions, speeding up the process.

As the pH declines, fewer nutrients are available to the plant. That forces farmers to apply even more fertilizer to get the same yields.

Some soils in the region are now well below a pH of 5 in the top 6 inches of the soil, “which is where you plant the seeds and they germinate.” Some farms are “extremely, severely” acidic, with a pH as low as 3.6 or 3.7.

“They were able to grow crops and within about a year or two years, they couldn’t grow anything,” Carter said. “It happened that fast.”

To rebalance the soil pH, farmers apply calcium limestone or dolomite limestone, which break down into calcium and carbonate in the soil. The carbonate forms carbon dioxide and water. The oxygen combines with the hydrogen in the soil.

Most farmers in the region don’t ordinarily apply agricultural lime. It’s a common practice in many regions, including Indiana, where Carter farmed with his father and brother.

“The rest of the world puts lime on fields because they know they have to,” Carter said. “Why do we think we don’t? That one escapes me. I just don’t understand the thinking, or lack of it.”

Over the past eight years, Carter has studied the economics of applying agricultural lime. In one experiment, he applied $200 worth of limestone and micronutrients per acre on an experimental plot near Walla Walla.

“The extra yield I got off of them would have paid for all the inputs,” he said. “In less than five years, we would have covered the cost of those inputs. So now it’s making money.”

“Paul just wants to get the science out there,” said Walla Walla area farmer Robert McKinney, who has worked with Carter on liming research.

The biggest issue for farmers is that it takes time to see results, McKinney said.

“The science is there — all of us are leery of putting a lot of money into something that doesn’t get immediate results,” he said. “Yeah, four or five years (to get a) return, but you’re going to see the results of that lime for quite a few years.”

Steve Van Vleet, WSU Extension educator in Whitman County and interim director of Columbia County Extension, praised Carter for his drive and focus on soil nutrition, even when few other researchers were looking at it.

“...(W)anting growers to adopt changes that will benefit their farms — Paul has been key for that,” he said.

There’s no question that Carter’s research will help ease grower concerns, McKinney said.

“He is trying to help us help ourselves,” he said.

“It’s taken 70 to 100 years to get to this point,” Carter said. “You’re not going to turn around and correct it like you do with fertilizer in one year.”

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