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ORSoilTests

The diversity of soils in Klamath Falls, Ore., and the Klamath Basin and their differing use histories mean one remedy will not solve all soil challenges.

“The Soil Survey of Klamath County, Oregon,” a 2-inch volume of technical words and fold-out maps produced by the U.S. Department of Agriculture, lists over 60 series of soils, each with characteristics and locations distinct from other soil types in the area.

Yonna soils “consist of very deep, poorly drained soils on flood plains. These soils formed in mixed alluvium that includes ash. Slopes are zero to two percent.” Shanahan soils, on the other hand, “consist of very deep, somewhat excessively drained soils on terraces, benches, and escarpments. These soils formed in an ashy mantle over a loamy buried soil. Slopes are zero to 45 percent.”

For those desirous of becoming more intimate with their soil’s profile, copies of the soil survey are available for onsite reference at Klamath Basin Research & Extension Center at 6923 Washburn Way, and also online at https://bit.ly/2Cg5hNK. Most people, however, just want more practically applicable information about how to improve their soils.

Evaluation methods

In short, soils are always improved by the addition of organic matter. We’ll explore soil improvement in a later column — first, understand that the diversity of soils in our area and their differing use histories mean one remedy will not solve all soil challenges. To modify soils to the greatest advantage, we must first understand what we are working with. Following are five different evaluation methods that will help demystify soil.

Mason jar stratification test. Start with a representative soil sample — meaning you get trowels full of soil from the root zone, from all over the area to be evaluated, combine them, and take a subsample of that batched sample. Fill a Mason jar halfway with soil, fill with water, shake, set aside. Particle sizes settle out at different rates. In most soils, you’ll observe three distinct layers: sand at the bottom, silt in the middle, and tiny clay particles settle out last, on top.

The ratio of sand, silt, and clay in your soil informs you about its drainage, its ability to hold moisture and nutrients, and its structure. For detailed info on interpreting the soil layers that result from your stratification test, see the USDA’s “Guide to Soil Structure” at https://bit.ly/2l3MMWi.

Ribbon test. If you’ve ever seen a farmer take a ball of moist soil and manipulate it in his fingers, he wasn’t just playing in the dirt. He was performing a ribbon test. When that ball of moistened soil is squeezed between the fingers, some soil types will form a “ribbon” — a continuous, flattened aggregate of soil. Sandy soils won’t ribbon at all — these will drain very quickly. Ideal soils form a ribbon around an inch long — ribbons two or more inches long, suggest soil heavy with clay and prone to poor drainage.

Drainage test. Sometimes called a percolation test, and helps to determine whether your planting spot has the “well drained soil” so widely recommended for garden plants. Dig a hole a foot across and deep. Fill it with water, let sit overnight. The following day, fill the hole with water again, and measure the rate of drainage. Less than an inch an hour will be problematic for many plants. Ideal drainage might be around 2 to 4 inches per hour. Faster rates imply your sandy soil will not hold water long enough for plants to take advantage of it — and you may need to water much more often.

pH test. Many Klamath soils have a pH around 7, a neutral reading that works for a wide range of plants. Our soil variability, however, especially on steep slopes, results in pockets of more acid or alkaline soils. Some plants, like blueberries, require a very specific soil pH range to thrive. When pH is off, plants can’t access nutrients properly, even when fertilizer has been applied. Many home pH kits are unreliable — take advantage of the free service offered by the Klamath County Master Gardeners to test your soil pH. Soil testing at the Klamath Master Gardeners plant clinic will be conducted on Fridays during the 2019 season (April through September).

Diagnostic testing. If you have a new or problematic site, are considering major landscape renovation, or want a higher level of detail, a diagnostic soil test will be in order. Soil can be tested for fertilizing recommendations — growers use this type of testing to tailor the exact amount of fertilizer applied to what is needed, avoiding extra costs and runoff. Soils can be tested for heavy metals, pesticides, and nutrient content of amendments. For these, you’ll access a professional lab, and collect a sample according to the specifications of the particular test. For details on the types of tests and where to order them, see “Analytical Laboratories Serving Oregon” at https://bit.ly/2JaRiic.

Nicole Sanchez is horticulture faculty at OSU’s Klamath Basin Research and Extension Center. For more information on this or other gardening topics, contact Nicole at Nicole.sanchez@oregonstate.edu or 541-883-7131.