This year I had the opportunity to work in the UConn Soil and Nutrient Analysis Laboratory during the ‘spring rush’. During this time the Soil lab can get up to hundreds of samples a day. These samples may come in one at a time from homeowners with established lawns or garden beds who are looking to maintain their plantings or from new homeowners who have never planted or cared for a landscape before, or dozens of samples from commercial landscapers on behalf of their clients, or from commercial growers.

For over 50 years farmers, greenhouse growers, and homeowners have been served by the UConn Soil Lab. With more than 14,000 samples coming in on an annual basis, that is a lot of soil! Soil fertility is the first building block of plant health. If a plant is not growing in soil that has the proper proportion of available nutrients then it will not grow as well as it could. Poor soil health leads to stressed plants with stunted growth and stressed plants are vulnerable to insect and disease issues.

Iron deficiency on buddleia

Buddleia with iron deficiency

There are a minimum of 16 elements that have been deemed necessary to vigorous plant health. In order by atomic weight they are: hydrogen, boron, carbon, nitrogen, oxygen, magnesium, phosphorus, sulfur, chlorine, potassium, calcium, manganese, iron, copper, zinc, and molybdenum. Some other elements that may not be used by all plants are sodium, silicon, vanadium, and cobalt. The big 3 are, of course, nitrogen, phosphorus, and potassium. Represented by their symbols from the periodic table as N-P-K, they are the prime ingredients in most fertilizers. The seedlings below show signs of nutrient deficiency and are in need of a weak solution of a balanced fertilizer.


Also essential to healthy plant growth is the pH of the soil. It won’t matter how much fertilizer is applied if the soil pH is not in the correct range for the host plant. pH stands for potential of Hydrogen and is represented by a scale that runs from 0-7 for acidic solutions and from 7-14 for the alkalis. The higher the concentration of hydrogen ions, the more acidic the sample is. All soil test results will recommend the addition of either limestone to raise the pH, sulfur to lower the pH, or no action required if the pH falls into the acceptable range for the plant/crop.

All standard nutrient analysis tests begin their journey in the same way. For each area to be tested one cup of soil is sent or brought to the lab along with the soil sample questionnaire. The standard test will provide soil pH, the macro and micro nutrients, the total estimated soil lead, and basic texture and organic matter content. Many homeowners and growers request additional tests or only require specific information in the form of textural analysis, organic matter content (measured by Joe in the images below), soluble salts, a pH only test, saturated media analysis (for soil-less potting media for greenhouses), or nitrate testing (for commercial growers).


This spring was very cool and wet, as we all know. Many samples were sent in later than usual and a good many were very much wetter than usual. It is important then that the first step requires that soils be spread onto paper toweling and allowed to dry.

1. Spread soils on drying rack

Once the soil has adequately dried out it must be sieved so that any rocks or bits of organic matter are removed. This step may also involve some pounding to break up any chunks of soil as shown by Skyley.


From there a small amount of each sample is placed in a paper cup by Louise to be tested for its pH. It is mixed into a slurry with a small amount of distilled water, the calibrated testing meter probe is placed in the mixture and the pH level is stored in the computer program for later retrieval.


In a manner similar to a coffee pour over, some of the soil is placed in filter paper that is resting in a test tube in preparation for the nutrient analysis. A Modified Morgan solution is the liquid used for this extraction method.


The nutrient analysis is done by a machine called the ICP which stands for Inductively Coupled Plasma. This machine would be right at home in Abby’s lab on NCIS! When I was in school back in the 70’s we were taught that matter existed in three states: solid, liquid, and gas. But matter has a fourth state and it is plasma. It doesn’t exist on Earth under normal conditions but we do witness it every time we see a lightning strike.  Plasma can be generated by using energy to ionize argon gas.

The plasma flame is hot. Really hot.  6000 Kelvin.  For some perspective, the surface of the sun is approximately 5,800 K.  The solution from the individual tube samples is passed through a nebulizer where it is changed to a mist that is introduced directly to the plasma flame. A spectrometer is then able to detect the elements that are present in the soil sample.


Additionally, the testing for phosphorus is done with this machine shown below, the Discreet Analyzer.


Some soil samples come from outside of CT and those may present a particular set of problems. The USDA has quarantines in several states to limit the spread of certain invasive insect pest species such as the imported fire ant, golden nematodes, and even a few plant species. For more information visit the Federal Domestic Soil Quarantines site.

Working at the UConn Soil Lab has been a great experience and quite an eye-opener. Who knew that there was so much behind a soil test?

Susan Pelton

All images by S. Pelton, 2108