UNH Cooperative Extension Soil Testing
The choice of soil test methods used vary from state to state and it is important that the method chosen is reflective of soil, climate and research results conducted in the state or area you live. In New Hampshire we use a Mehlich 3 extractant which was developed in North Carolina in the 1980s. We changed to this extractant in the early 90s because of its ability to accurately extract nutrients and metals over a wide range of soil characteristics. In recent years it has also been found very useful in predicting environmental risk for nutrient movement, especially phosphorus.
The Standard Gardening Test on the Home, Grounds & Garden form includes conventional and organic recommendations; nutrients include extractable calcium, magnesium, potassium and phosphorus; organic matter content, and soil pH. Also included is a soil lead screening analysis.
The Field Test on the Biosolids, Commercial Corn, Forage & Pasture, Commercial Fruit, Commercial Vegetable, Christmas Trees and Non-Commercial Hay & Pasture forms includes conventional fertilizer recommendations; extractable calcium, magnesium, potassium and phosphorus, along with pH and Mehlich lime buffer pH. Results include calculated Cation Exchange Capacity (CEC), base saturations and phosphorus saturation.
The Field Test on the Commercial Field Nursery and Commercial Landscape form includes conventional fertilizer recommendations; extractable calcium, magnesium, potassium and phosphorus, along with pH.
Standard Compost - Includes percent solids (and moisture), organic matter, pH, soluble salts, total nitrogen, total carbon and the carbon to nitrogen ratio (C:N). This test is recommended as an initial test for feedstocks to help determine appropriate mixing ratios.
Standard Compost with Extracted Nutrients - Includes percent solids (and moisture), organic matter, pH, soluble salts, total nitrogen, total carbon and the carbon to nitrogen ratio (C:N), plus ammonium nitrogen, phosphorus and potassium.
Standard Compost with Total Nutrients - Includes percent solids (and moisture), organic matter, pH, soluble salts, total nitrogen, total carbon and the carbon to nitrogen ratio (C:N), plus ammonium nitrogen, phosphorus and potassium, plus ammonium nitrogen, phosphorus, potassium, aluminum, calcium, magnesium, manganese, sodium, copper, iron, sulfur and zinc.
The Mehlich 3 extractant is used to remove nutrients from your soil sample in an amount that is reflective of how much is available to the plant. Due to the volatile nature of nitrogen in the environment, nitrogen analysis is not preformed on basic soil samples. The amount of nitrogen needed by the crop is estimated based on the field history, certain soil characteristics, organic matter content if available, and the crop to be grown.
Organic Matter Content:
For soil samples, a measured amount of soil is weighed and heated to 360 degrees C to burn off the combustible part of the sample. This represents the organic portion and is related to the amount of residual nitrogen available to the crop. For composts, the determination is similar but at a higher temperature (550 degrees C).
This procedure determines the amount of sand, silt and clay along with the textural class as determined by the relative percentages of the three soil fractions. This test is sometimes used by landscape architects, golf course superintendents, municipal park managers, and those who supply sand, soil and other mixtures used by these professionals in maintenance and construction activities. For further information contact your county office of UNH Cooperative Extension.
A lead screening analysis is included in the Home, Grounds & Gardens test. If lead levels are high, we sometimes recommend a "Total Lead" analysis based on the US Environmental Protection Agency Method (USEPA) 3050/3051 plus 6010. This will provide a more accurate picture of the risk of lead contamination in your soil sample and whether you need to adjust your plans for gardening and use of the area.
Environmental Package (Heavy Metals):
This test measures the levels of six trace elements sorbed (held on) to the soil. The method used is USEPA method 3050/3051 plus 6010. This test can assist in monitoring soils that have been amended with residuals or other materials. An individual soil test for lead can also be run when it is recommended by the lead screening test (part of the homes and grounds soil test package).
Plant tissue analysis is a valuable tool in a crop management program. In NH, the major use of this analysis is in commercial fruit production such as apples, blueberries and strawberries. For more information contact your local county Extension office.