Wheat residue study

A researcher advises wheat farmers to make sure they retain an adequate amount of residue each year.

Growers should compare the value of what wheat straw does for their fields with the price they could sell it for, a USDA soil scientist says.

David Huggins, a soil scientist with the USDA Agricultural Research Service in Pullman, studied the impact of removing straw on soil health and whether removing it would reduce the amount of nutrients such as nitrogen, phosphorus and potassium and the cost of replacing them using fertilizer.

“If (farmers are) going to haul off their residue, they should consider being paid for at least the fertilizer value of that residue,” Huggins said. “Those are very real kinds of exports and nutrients they’ll have to replace eventually.”

Winter wheat residue has a nutrient value of about $13 per ton, Huggins said.

Standing residue also conserves water. It retains 1-2 additional inches of water in the soil, which translates into roughly 5 to 10 more bushels per acre, Huggins said.

Residue also feeds the soil, prevents erosion damage and provides cover for wildlife.

“It needs so much residue returned to the soil every year in order to maintain our organic matter,” Huggins said. He estimates 4,500 to 5,000 pounds per acre are needed every year.

Winter wheat typically produces more than that. One hundred bushels of wheat produces about 10,000 pounds of residue, he estimated.

“That’s more than enough to supply organic matter, but we don’t grow winter wheat every year,” he said. “We’re also growing crops like garbanzo beans, which don’t produce nearly the same amount of residue, so the winter wheat has to compensate for those other crops.”

Huggins recommends growers who harvest residue consider continuous no-till farming.

“The tillage combined with residue removal is a double threat to maintaining soil organic matter,” he said.

“In some locations you’re hauling off 2 to 4 tons of wheat residue per acre, that starts to add up,” he said. “If farmers can take those numbers and start to consider, ‘How much should I expect to get for some of this residue?’ they might just consider the nutrient value in and of itself.”

Are there any positives to removing crop residue?

Huggins said it could be the first step in finding new weed management tools.

“Certainly, if farmers are actually getting an economic return from this, that can be a positive thing that should be looked at in the short term,” he said. “But I am concerned about the long-term impacts on our soil resources.”

John Begley is CEO of Columbia Pulp, which is opening a plant in Starbuck, Wash., that will turn wheat straw into dry pulp and biopolymers.

Begley said many studies “somewhat biased or pre-disposed” against removal of crop residue, and present data to support that narrative.

He said the question is whether there’s an excess of residue.

According to Columbia Pulp, the company annually takes a small fraction of all straw in Eastern Washington. It will not take from the same field year after year, so there will be little impact on any particular field. The company will consume “only a very small portion” of annual straw residue in eastern Washington, or Columbia, Walla Walla and Garfield counties.

“The cost of replacing nutrients lost to baling is significantly less than the revenue gained from selling straw,” Begley said in an e-mail to the Capital Press.

According to Columbia Pulp, the portion of straw residue transformed into biopolymer during the cooking process contains lignin and carbohydrates in a form that is more readily mineralized by natural soil processes.

The company actively plans to return a substantial portion of that biopolymer to agricultural sites.

The biopolymer is alkaline so reapplication to wheat growing sites will tend to increase soil pH. This could help to reverse the acidification caused by current fertilization practices, according to the company.

Field Reporter, Spokane

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