10 Easy Soil Tests

Find out if your soil is ready for planting.

By Julie Monahan

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Test 6. Plant Residue

If you've grown a cover crop, dig down 6 inches 1 month after turning it into the soil and then look for plant matter. The range of organic material is important to notice here. The presence of recognizable plant parts as well as plant fibers and darkly colored humus indicates an ideal rate of decomposition.

Why it's important
"The single most important component of healthy soil is organic matter," Thompson says. But plants and other organic materials decompose only when soil organisms are there to do the work. Any sign of this process is a good sign, but the speed of decomposition is important, too. Fast decomposition is another indicator of soil quality. In poorly aerated soil, plants break down slowly, a condition that gives off a faintly sour scent.

Test 7. Plant Vigor

Start this test during the active growing season and look for healthy plant color and size that's relatively uniform. Overall health and development must be judged for what's considered normal for your region. One caveat: If you planted late or during a drought, or suffered a pest infestation, results of this test may be unreliable.

Why it's important
Plant vigor indicates soil with good structure and tilth, a well-regulated water supply, and a diverse population of organisms. It's the best sign of effective soil management you'll have above ground.

 

Test 8. Root Development

Use a shovel or hand trowel to dig gently around a selected plant, preferably a weed you won't miss. Once you've reached root depth, pull an annual plant up and check the extent of root development, searching for fine strands with a white healthy appearance. Brown, mushy roots indicate serious drainage problems—and a poor outlook for this year's harvest. Stunted roots might also indicate disease or the presence of root-gnawing pests. "When you look at the roots, you can really see what's going on," Allmaras says.

Why it's important
Roots have the most immediate connection with and reliance on soil quality. Without air, water, biological activity, and crumbly soil to grow in, roots can't do their job.

Test 9. Water Infiltration

Take an empty coffee can with the bottom removed and push it into the soil until just 3 inches remain above the surface. Fill the can with water, marking the water height, and then time how long it takes for the water to be absorbed into the soil. Repeat this several times until the rate of absorption slows and your times become consistent. Anything slower than 1/2 to 1 inch per hour is an indication of compacted soil.

Why it's important
Good infiltration gets water to plants where they need it—at their roots—prevents runoff and erosion, and lets air move more efficiently into soil pores.

Test 10. Water Availability

Wait for a soaking rain; then record how long until plants start to show signs of thirst. Results will vary widely by region. The basic lesson is that if plants require more frequent watering than typical for your region, your soil is probably the culprit.

Why it's important
Porous soil can better resist evaporation and adequately supply plants between waterings. "It could make all the difference in the world if water were to go another inch deeper," Allmaras says.

The Willamette Valley Soil Quality Card Guide, on which this article is based, provides you with even more information and guidance on evaluating your soil and how to improve it based on the results of this test. Get a copy from the Oregon State University Extension Service.

Julie Monahan gets her hands dirty counting earthworms in her Seattle garden.

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