David Granatstein of the Washington State University Center for Sustaining Agriculture and Natural Resources speaks at a soil health workshop on March 16, 2017, in The Dalles, Oregon. TJ Mullinax/Good Fruit Grower
At a soil health workshop organized by Oregon State University in the Dalles, Oregon, several speakers sang the praises of mulch.
Mulch works to damp down weeds, protect soil moisture, and keep the soil surface cool, but it also provides a long-lasting carbon source that stimulates many key soil organisms, said David Granatstein, with the Washington State University Center for Sustaining Agriculture and Natural Resources.
“There’s an incredible amount of life below ground. It’s there to work for you if you encourage it, feed it, and give it a good home,” he said.
For example, mulch encourages populations of the predatory nematodes that eat plant parasitic nematodes, so mulching can boost that biocontrol, Granatstein said. A tart cherry study in Michigan found mulch treatments provided the highest yields and his own research in Gala apples has shown the mulch reduced the need for irrigation by 25 percent and increased apple profit by $4,700 an acre, including the cost of hauling the mulch.
But the benefits he described don’t necessarily require hauling in wood chip mulch. Mow and blow experiments in Washington Honeycrisp blocks have shown increased root function, tree health, and better outcomes in terms of fruit storage, said Gary Johnson of Wilbur Ellis. The mowed mulch provides nitrogen and carbon to the trees, but it also creates organic matter that changes the soil structure to encourage root growth and water retention, he said.
“When you start to dig, you’d be shocked to find how rare functional feeder roots are in our orchard rows,” Johnson said. “If you want to grow better trees, grow more roots.”