Homegrown Soil-Health Tests

Lynn Betts, Contributor

You don’t need fancy equipment or laboratories to find out if your soil is healthy. While scientific tests are helpful, soil-health advocates urge growers to start testing by digging in to look, feel and smell the soil.

“You can learn a lot by taking a spade with you to the field,” says Rick Bednarek, state soil scientist for the USDA Natural Resources Conservation Service in Iowa. “First, you’ll know immediately that you’ve got a problem if you have to jump on a spade just to get it in the ground. Then, see if that spadeful of soil crumbles and looks like cottage cheese, or if it’s blocky looking,” he says. “If the soil is blocky, you probably have compaction.”

Plant roots can also tell a story about compaction, Bednarek points out. If roots are growing sideways, it’s another sign of compacted soil. A darker color indicates the soil has more organic matter.

GIVE IT A PUSH

The first tool Denny Winterboer, Milford, Iowa, pulls out to benchmark and monitor soil conditions is a penetrometer. This simple $200 item registers how compacted the soil is and locates depths of multiple layers of compaction. It measures penetration resistance in pounds per square inch. Few plant roots will penetrate into soil with a resistance of more than 300 pounds per square inch.

THE JAR TEST

If you want a comparison of your soil against a healthy soil, Bednarek suggests gathering a spadeful of soil from an old fencerow. If you’ve been tilling your soil for years, you’ll likely see differences in how the spade goes in the ground, how crumbly the soil is and how dark it is.

A couple of quart jars filled with water are all the tools needed to check soil stability.

“Drop a clod or clump of soil from the fencerow into one of the jars and a clod from your field into the second jar at the same time, and watch to see what happens to the soil,” Bednarek says. It’s called the slake test. “If the soil falls apart and quickly crumbles to the bottom of the jar, you have poor structure with poor aggregate stability.”

Bednarek says that’s important, because the same thing happens to the soil when it rains. “If the soil breaks apart into finer particles, those particles fill pore spaces--that inhibits infiltration, leading to more runoff and soil erosion,” he says.

RING THINGS

You can check and compare infiltration rates yourself with infiltration rings. “Infiltration rings give you an idea of how fast water will infiltrate into your soil after a heavy rain,” Bednarek says. “Just place the rings firmly into the soil and pour an inch of water into them, timing how long it takes for the water to soak into the soil. I’ve seen an inch of water disappear into the soil in 10 to 15 seconds in a healthy soil on the first pour,” he says.

“That first inch of water can also disappear quickly in soils that are tilled up like a garden,” Bednarek says. “The second inch is the one to watch. It acts more like a heavy rain. That second inch will be absorbed within 10 minutes in a healthy soil, but I’ve watched poor soils for 45 minutes and water was still sitting there.” There are 3-inch diameter steel rings available for sale, but you could also use a fruit or vegetable can with top and bottom removed.

DIRTY DRAWERS

Reinbeck, Iowa, farmer Jack Boyer has been employing all sorts of testing since cover crops went into his rotations seven years ago. He used the commercial Haney test to measure soil health last fall.

But, he’s also used more seat-of-the-pants testing. Working with Iowa State University and Practical Farmers of America, he buried ordinary tea bags about 5 to 6 inches deep, leaving the tags on the soil surface so they can be found.

“You weigh the bags before you place them in the soil, and then weigh them when you dig them up, measuring how much the microbes have consumed,” Boyer says. “I’m comparing microbial activity in corn with and without cover crops.”

He’s also tried the popular test of burying men’s cotton underwear. After several months, you dig them back up to see if soil microbes are at work and the biological activity in the soil. Boyer also digs soil pits on the farm to compare roots, channels in the soil and other characteristics.

Bucketful of Soil-Health Tools:

About four years ago, NRCS challenged the Murray FFA chapter in southern Iowa to fill a 5-gallon bucket with the tools and instructions that a farmer or conservationist could use to gauge soil health. The group now sells the soil-health test buckets as a fund-raiser.

They come filled with two aluminum infiltration rings, a hand shovel, a thermometer, jars for the slake test, pH test strips, nitrate/nitrite and orthophosphate test strips, phosphorus test strips, a soil organic matter color chart, a calculator, a knife, the Solvita soil life respiration kit and other testing accessories.

A Soil Health Kit Guide provides the instructions for testing such things as soil bulk density, organic matter, respiration, electrical conductivity, pH, nitrogen and phosphorus levels, and infiltration.

Iowa NRCS officers have added to the buckets to include a penetrometer--they’re equipped to work with farmers who want to benchmark or check their fields for soil health. To receive pricing information and to order, call or email the Murray FFA at 641-447-2517, or email smiller@murraycsd.org.

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