Soil Testing
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Why should you test your soil?
Whether working in your garden or on your farm, understanding the condition of your soil is key to growing healthy plants. Crop producers and gardeners can both gain useful information from a few simple tests. Soil testing reveals the available nutrients that help your plants grow and can help you determine what is needed to increase plant health.
There is a lot going on underground!
While looking at the plants growing on top of soil can give us a good sense of overall health, there is much more that can be learned by digging deeper. Identifying the texture, type, and chemical components of the soil helps determine what it is best suited for, whether that be crop production, habitat creation, infrastructure building, or something else. It will also help decide which plants will grow well. You can test the physical, biological, and chemical characteristics of soil to get a sense for its overall health.
Find out what soil type you have:
Every soil in the world has been classified as a certain type. Soils are named and classified based on physical and chemical properties – which are determined by how they were formed
- Fun fact:
There are over 2,000 [1] different soil types within Oregon!
Knowing the local soil type may not be relevant for the home gardener (since many soils have already been greatly altered), but it can be very informative for farmers or developers. Soil type can provide clues about whether the land is typically wet or dry, and if it is well-suited for agriculture or can support large structures like roads and buildings. Soil types have been mapped across the country. You can find out what type of soil you have by visiting the Web Soil Survey.
Testing the physical characteristics of your soil:
For the home gardener, determining the texture of your soil will likely provide enough information to make appropriate plant choices. Soil texture is defined by the proportion of sand, silt, and clay particles that are present. Soil with high sand content will feel gritty, while a clay soil will be smoother. The texture of a soil indicates its ability to drain water, allow air flow, and hold nutrients. To measure the texture of your soil, try the squeeze test, ribbon test, or the jar method.
Other tests of physical characteristics include examining soil color, infiltration (the ability for water to move through the soil), and bulk density (a measurement of how compacted the soil is).
Testing the biological activity in your soil:
This one is easy – just Soil Your Undies! We’re serious – join this fun international effort to test soil health.
Burying a pair of cotton underwear in your soil is a simple, cheap way to get a sense for how active the microbes in your soil are. Bury the underwear about 3 inches deep in the soil. Wait at least 60 days, then dig up the underwear and take a look. The more tattered they are, the healthier your soil microbes are!
How does this work? Soil microbes break down and decompose the cotton material of the underwear. If you have a very active microbial community, you might find that the elastic band is the only thing left intact. If your underwear came up looking good-as-new, you’ll likely want to think about amending your soil to boost the microbial activity.
Looking for an even simpler way to assess biological activity? Try an earthworm count.
Testing the chemical composition of your soil:
Anyone looking to produce crops on their property would benefit from conducting a chemical analysis of the soil every three to five years. A simple pH estimate can be made using an inexpensive sensor. Soil pH is a measurement of how acidic or alkaline your soil is. The pH measurement is a good indicator of the availability of nutrients for uptake by plants. Most plants fare best in soils that are neither highly acidic nor alkaline (pH = 5.5 – 7.5).
For more in-depth analysis of the nutrients in your soil, you can collect soil samples and send them to a lab for testing. Standard soil testing results include values for organic matter, phosphorus, potassium, calcium, magnesium, and sodium. All of these values can help you determine which crops will thrive in your soil or what types of amendments or fertilizers the soil needs, if any, to be most productive.
To collect soil for a chemical test, follow the instructions in Oregon State University Extension’s Guide to Collecting Soil Samples. You can also find a list of testing labs on their website. Once you have your test results, refer to the Soil Test Interpretation Guide for recommendations.
