Soil Testing

The soil test is an excellent measure of soil fertility. It is an inexpensive way of maintaining good plant health and maximum crop productivity. Soil fertility fluctuates throughout the growing season each year – the quantity and availability of mineral nutrients are altered by the addition of fertilizers, manure, compost, mulch, and lime or sulfur, in addition to the process of leaching. Furthermore, a large quantity of mineral nutrients are removed from soils as a result of plant growth and development, and the harvesting of crops.

The soil test will determine current fertility status. It also provides the necessary information needed to maintain optimum fertility year after year. Some plants grow well over a wide range of soil pH, while others grow best within a narrow range of pH. A soil test is the only precise way to determine whether the soil is acidic, neutral, or alkaline.

Most soil nutrients are readily available when soil pH is at 6.5. When pH rises above this value, nutrient elements such as phosphorus, iron, manganese, copper and zinc will become less available. When soil pH drops below 6.5, manganese can reach a toxic level for some sensitive plants.

The soil test takes the guesswork out of fertilization and is extremely cost effective.  It not only eliminates the waste of money spent on unnecessary fertilizers but it also eliminates over-usage of fertilizers, hence helping to protect the environment. 

Sampling can be done at any time, but late October or early November is usually  preferable. Avoid sampling when the soil is very wet or recently limed or fertilized. Soils that look different or have been used differently should be sampled and tested separately. Areas where there is poor growth should also be tested separately.

  Using a trowel or spade, take about ten thin, vertical slices of the soil. Put slices of soil on newspaper to dry at room temperature (do not dry samples in an oven or on a stove or radiator) and then put soil into a large, clean plastic container or bag and mix  thoroughly. Take about one cup of soil mixture and put it in a sandwich size "zip" type plastic bag and close tightly. Label each sample on the outside of the bag. This should then be mailed to The University of Massachusetts Cooperative Extension, Soil Testing Laboratory, which offers a variety of soil test options for home gardeners and commercial growers. A soil test form and instructions is available on the URI Master Gardener Website at www.urimga.org A fee for each sample must be enclosed; samples received without the proper fee will not be tested.

A "Standard Soil Test" checks for:

• pH and lime requirement

• levels of available plant nutrients

• abnormally high levels of several toxic elements

Based on this test, the testing lab sends recommendations on the amounts of lime and fertilizer to add to the soil and what action to take should an unusually high level of lead be present.

Other tests offered are:

• pH: This test is the same pH test performed as part of the standard soil test.

• Soil Textural Class Analysis: This test provides percentages of sand, silt, and clay in the soil and determination of the USDA Soil Textural Class.

• Organic Matter: This test provides the percentage of organic matter in the soil.

Adapted from: Ohio State University Extension; University of Rhode Island Cooperative Extension