Soil testing helps determine which elements and nutrients are readily available for plant growth in the soil. In addition, testing can also reveal the soil pH, exchangeable acidity and humic matter. The results help a gardener determine the proper amount of fertilizer, amendments and organic material to add to the soil. According to the Virginia Cooperative Extension, the reliability of the soil test depends on the soil sample collected. The proper soil testing equipment helps a gardener take the correct samples for testing.
Use a shovel, spade or hand trowel to collect a soil sample. Use clean tools made of materials other than brass, bronze or galvanized steel, which taint soil samples with copper and zinc. Make a vertical cut with the shovel, 4 inches deep for lawns or at plowing depth for a field or garden. Another vertical cut should remove a V-shaped wedge of soil from the ground. Remove a thin slice, approximately 2 inches thick, from the smoothest side of the opening.
Soil probes, also called tubes, are available through agriculture suppliers and local extension agents. Costing $25 and up, as of 2009, the soil probe removes a round plug of soil from the dirt when pushed down. The soil probe allows you to remove a continuous core of soil with little disturbance to the surrounding soil. The soil probe provides for faster sampling, making it convenient when you need to take several samples.
However, the soil probe must be used when soil conditions are just right. If the soil is too wet, the soil will compact. If the soil is too dry, it will be hard to push the probe into the ground. Soils that contain high levels of gravel or rock are difficult to collect with a soil probe.
Once the soil sample is removed from the ground it should be mixed in a clean, plastic bucket. If the bucket has held fertilizer or chemicals, thoroughly wash and rinse before using. According to the Virginia Cooperative Extension, even the smallest amounts of lime or fertilizer can contaminate a soil sample.
Home Test Kits
For a small garden, a home soil test kit gives fast results. The kit usually contains four tests: pH, nitrogen, phosphorus and potassium. While not as comprehensive as testing by an extension office, the home test provides key information for small gardens or those in areas where extension offices don't offer testing. Purchase test kits at home improvement stores and agricultural centers for less than $20, as of 2010.