New tests measure soil health

Until now, a major piece of the soil quality puzzle has been missing. For decades, traditional soil tests analyzed nutrients, soil pH, and organic matter, leaving out soil biology.

But two new tests give growers objective tools to track the impact of their management changes and measure if practices like compost, manure, ­growing a cover crop, or adding a soil biostimulant are making a difference.

“Managing soil health is not black and white.”
—Dr. Don Horneck

Managing soil health has always been difficult, says Oregon State University’s Dr. Don Horneck.

In the past, laboratories measured physical and chemical components of soil; there wasn’t a way to measure soil biology, the third component of soil health, said Horneck, an agronomist at OSU’s Hermiston research station. New tests give growers a chance to learn about available nutrients and decide if management practices improve soil health.

The Soil Health Nutrient Tool, also called the Haney test, was developed by Rick Haney, a scientist at the U.S. Department of Agriculture’s research laboratory in Temple, Texas, and Woods End Laboratories of Maine. The Haney test is being adopted by no-till and cover-crop farmers in the Midwest, many of whom have cut their fertilizer in half as a result.

The Haney test uses nonproprietary methods to extract soil samples with water, measuring organic carbon and nitrogen—food that’s available to soil microbes. It also measures the soil’s carbon-to-nitrogen balance, microbial active carbon, water-soluble carbon, and the carbon dioxide rate, an indicator of microbial activity. The test gives an overall soil health score ranging from 1 to 50.

The collaboration between the USDA and Woods End lab on the Haney test led to development of a quick and easy test kit to measure soil carbon dioxide respiration. Woods End has patented the Solvita Soil Test, which can be purchased by commercial labs or growers for field testing.

The second test, developed by Cornell University, goes a step further than the Haney test by using the soil sample to grow a plant in a greenhouse and score how the plant grew, what diseases were present, and such. Thirty-nine soil characteristics are evaluated on a scorecard. The Cornell test takes four to six weeks because it involves growing a plant.

Though Horneck prefers the Cornell test because it is more comprehensive, both tools provide what was previously lacking—a way to measure overall soil health, soil food, soil activity, and the balance of the two.

He believes the tests could be valuable in assessing a potential site.

The Cornell test is conducted at Cornell University; at least three laboratories perform the Haney test—Woods End, Brookside Laboratories in Ohio, and Ward Laboratories in Nebraska.

Organic matter

In the past, soil organic matter was used to measure soil health, Horneck said during the annual meeting of the Washington Association of Wine Grape Growers held in Kennewick, Washington. “Organic matter is magical stuff in the soil and crosses all three properties of soil: chemical, biological, and physical.”

Soils high in organic matter are more forgiving during drought because they hold and supply more water and nutrients.
“Organic matter is a key indicator in soil health,” he said, but added that it doesn’t necessarily equate to soil quality or fertility. Soil organic matter in Washington’s Columbia Basin is naturally low, ranging from 0.5 to 2.0 percent. However, some of the state’s top-selling wine grapes are produced from vineyards with low organic matter.

Horneck noted that soil texture plays a role in organic matter, as does temperature. Soils in the Columbia Basin are sandy, temperatures are hot, and rainfall is low, all which make it difficult to significantly increase organic matter.

“You’re not going to increase Columbia Basin soil that’s at 0.5 percent organic matter to 6 percent if the soil is 99 percent sand—at least not economically,” he said. “Under such conditions, the roadblocks are too big and soils too well drained to think you can build soil organic matter levels above 1 to 2 percent.”

Practices that are destructive to organic matter include tillage, removing crop residues, and burning crop residues. Tillage has been shown to be one of soil’s biggest enemies and is detrimental to soil health because it increases oxygen levels and allows release of carbon dioxideinto the atmosphere.

Growing a perennial crop and keeping roots in the soil as long as possible is one of the best things for soil. Applying compost and manure and growing a cover crop are also ways to improve soil organic matter.

But there’s a big difference between applying manure and compost, Horneck said. “Compost is like adding organic matter. It’s already gone through the biological breakdown and can last in your soil for twenty years. Manure is more like adding fertilizer and may last only a couple years. Think of compost as a soil amendment; manure as a soil fertilizer.”

A cover crop is like a fertilizer, he said, but it also adds biomass.

Though there are ways to increase organic matter, in many locations, it becomes a math problem. For example, adding humic acid to the soil can increase organic matter, but it takes a lot of material to make a change. One percent organic matter in the top foot of soil equals about 40,000 pounds—it’s hard to add enough material to make a significant difference, Horneck explained.

Voodoo products

He believes the new soil tests will help growers learn if different products work in their soils. “Managing soil health is not black and white,” he said. “There’s this whole mesh of grayness in the soil, grayness comes from the land of voodoo. There are lots of products you can apply to your soils to make them perform better. But soil health is such a complicated, big issue that it’s hard to know what’s really working.” •