Soil tests are used as an informational tool to help you know how much fertilizer and other elements you should add to the soil for best results with your gardening. A soil test will diagnose your soil problems by letting you know what it's lacking or has too much of, so you know how to better accommodate your plants. Soil tests often measure nutrient levels, pH levels, exchangeable acidity and heavy metals.
To measure nutrient levels in a soil test, a chemical removal process takes out nutrients and then tests them to see how much of the nutrients are actually available to the plant. Some of the nutrients measured during this particular soil test are zinc, copper, calcium, potassium, magnesium, phosphorus, sulfur, sodium and manganese.
Determining soil pH-level is perhaps the most important aspect of a soil test. Knowing nutrient levels without pH levels won't help in improving your soil because pH level affects the way nutrients are absorbed by plants. Soil pH is rated on a scale from zero to 14 with lower numbers being acidic (high in hydrogen ions) and higher numbers being more alkaline, with 7 being neutral.
According to Garden Ville, an organic gardening specialist, “Nutrients in the soil are most readily available at a neutral pH. A high pH level can result in nutrients becoming less available, while a low pH can cause some nutrients to reach levels toxic to certain plants.” A neutral pH is 7 and most plants grow best between 6.5 and 7.2 pH levels. Aluminum sulfate is added to soil with a high pH, and agricultural limestone (lime) is generally added to neutralize acid soil.
Exchangeable acidity is a part of the soil test that will determine how much lime, if any will need to be added to the soil. According to Penn State University Extension, soil acidity has two components; active acidity, measured by pH levels, and exchangeable, or reserve, acidity. Exchangeable acidity is a measure of the amount of hydrogen ions held by the nutrients within the soil. It is used in conjunction with the standard pH reading to determine how much lime to add to the soil.
Heavy Metal Tests
In some areas you may need to have heavy metal tests performed on your soil, if there are regulations requiring such tests in your area. Even if such tests aren't a requirement you may benefit from knowing the measurement of heavy metals in your soil to improve it. Heavy metal tests usually include testing for the following possible soil components: lead, nickel, cadmium, arsenic, chromium, and selenium.