Plant health depends on several soil factors, including the presence of nutrients to be taken in by roots. Other soil elements determine how well those nutrients are made available. Utah State University soil scientists recommend that you test your garden soil at least every five years. County or university extension offices provide the most complete soil analyses. Gardeners must dig up small sections of soil from the garden and submit them for examination by laboratory technicians.
Plants require sufficient levels of three main nutrients to survive. Nitrogen, the key element for leaf and stem development, is not usually determined by soil nutrient tests. Nitrogen content changes constantly in soils and regularly must be supplemented during the year. Tests do detect levels of potassium and phosphorus, however. Low potassium (K) levels will inhibit root development. Phosphorus (P) is necessary for stem structure and flowering. Such tests will tell you whether your P and K levels are too low and thus require fertilizer applications or too high.
Soil pH Tests
A pH test indicates the soil's acidity. Acidic soil levels are lower than 7, while alkaline soils are higher than 7. Certain types of grasses, such as fescue, grow best at a pH level between 5.5 and 6.5. Most plants thrive in slightly acidic soils. Normally, pH test results come with recommendations as to whether the gardener should add lime to raise soil pH or other fertilizers to decrease it.
Other minerals such as calcium and magnesium benefit plant health. The numbers on a soil test report indicate pounds per acre. These figures are often followed by information describing whether the level is sufficient and fertilizer recommendations if warranted.
Soluble Salt Tests
If a soil contains too much sodium, or soluble salts, it can inhibit the plant's ability to absorb needed nutrients. High salt levels will also case the roots to "burn." A saline test will tell whether the gardener will need to take measures to reduce the sodium content of the soil.