# Soil pH – The Master Variable

The UConn Soil Nutrient Analysis Lab tests for and analyzes multiple soil parameters; but none as critical, and as often overlooked, as pH. Soil pH plays a crucial role in the growth of vegetation planted, as well as ground water quality. Before we start talking about soil pH, I think it is a good idea to try to define what exactly pH is, and how it is determined.

When most of us think of pH, a pool probably comes to mind. I remember growing up, watching my mother apply different chemicals to our pool, and impatiently wondering why I had to wait to go swimming. She would tell me that she was adjusting the pH of the water to ensure it was safe to swim in. The basic understanding is that pH is tells us how acidic, neutral, or alkaline something is. To get a little more technical, pH is the measurement of the activity of Hydrogen Ions (H+) in an aqueous solution. The equation for determining and quantifying pH is:

pH = -log10 (aH+)

(aH+= Hydrogen Ion Activity in Moles/L)

We express pH on a logarithmic scale of 0-14, where 0-6 is considered “acidic”, 7 is “neutral”, and 8-14 is “basic”.

Mineral soil pH values generally range from 3.0 – 10.0. There are numerous factors that determine soil pH including climate, parent material, weathering, relief, and time. Texture and organic matter content also influence soil pH. Most Connecticut soils are naturally acidic. Nutrient availability is directly influenced by pH with most plants (with some exceptions) thriving at pH values between 6 and 7. A majority of nutrients are available within this range.

Our lab measures pH using an 1:1 soil-to-DI water ratio. The saturated soil paste is mixed, then is analyzed using a glass electrode and a pH meter. We calibrate our meter using 2 solutions with known pH values, 4 and 7. We use these values because we expect most Connecticut soils to fall within this range. Once the initial pH value is obtained, a buffering agent is added. In our lab we use the Modified Mehlich Buffer. A second pH reading is obtained, and from these two values plus crop information, we are able to make limestone and/or sulfur recommendations.

The Buffering Capacity of a soil is the resistance it has to change in pH. Soil buffering is controlled by its Cation-Exchange-Capacity, Aluminum content (in acidic soils), organic matter content, and texture. A soil with a lot of organic matter and clay will have a higher buffering capacity than one with little organic matter that is mostly sandy.

If the soil pH is lower than the target range for a particular plant, limestone would be recommended. Whether you use pelletized, ground or granular limestone, the application rate would be the same. Once the target pH is reached, a maintenance application of 50 lbs/1000 sq ft would be applied every other year to maintain it.

If the soil pH is higher than desired, sulfur recommendations are made. Typically only powdered sulfur is available locally but granular sulfur could be mail ordered. Aluminum sulfate can be substituted for sulfur and used at a higher rate. Check out this listof preferred pH ranges for many common plants.

Monitoring your soil pH is essential to ensure that it is falling within the range best suited for the vegetation you are growing. The Standard Nutrient Analysis performed at our lab gives you a pH value, a buffer pH value, a lime/sulfur recommendation, available micro & macro nutrient levels, and a fertilizer recommendation. For more information on pH, you can contact Dawn or myself (Joe) at the UConn Soil Nutrient Analysis Lab (www.soiltest.uconn.edu). Test, don’t guess!

By Joe C.

# Soil Test Prices Have Increased

Starting July 1, 2016, the UConn Soil Nutrient Analysis Lab increased some of our fees as well as our offerings. The price of the standard nutrient analysis increased from $8 to$12. This is the test that is performed when a sample is submitted using those pre-paid soil test collection kits sold by some county offices. The standard nutrient analysis will now include sulfur, an estimated cation exchange capacity measurement and percent base saturation. A new interpretation sheet will be posted on our website. We are also increasing the costs of pH only and soluble salts tests from $3 to$4. The pH test is included in our standard nutrient analysis but sometimes a client just wants pH and not nutrients.

# Soil Testing for Lawns and Gardens

By Dawn Pettinelli for UConn Extension

Soil testing is an inexpensive, yet valuable, tool for assessing the fertility of lawn and garden areas. Test results indicate the soil’s pH level, the amounts of available plant nutrients, and the existence of nutrient imbalances, excesses or deficiencies.

WHY SHOULD I HAVE MY SOIL TESTED?

Soil testing eliminates the guesswork many gardeners face when deciding the kinds and amounts of fertilizers or soil amendments they should purchase and apply. Each soil test report contains recommended amounts of limestone and/or fertilizer needed for optimum plant growth. Knowing how much to apply saves time and money.

It is a smart decision to test the soil every few years. Further- more, it is particularly important in new garden bed installations or in established plantings that are not performing as well as expected. Regardless of whether you garden organically or use synthetic fertilizers, you will find that plants grow best when their nutritional requirements are met. This is achieved not only by the addition of nutrients such as nitrogen, phosphorus and potassium but also by sometimes modifying the soil’s pH through the incorporation of limestone or sulfur.

Soil pH is a measurement of the acidity of the soil. A pH of 7.0 is neutral, below 7.0 is acidic, and above 7.0 is alkaline. Native soils tend to be acidic. It may be necessary to raise the pH by adding limestone. Plant species vary in their soil pH preference. Blueberries and broad-leaved evergreens, such as rhododendrons, may develop iron deficiencies if the soil pH is too high. Lack of calcium from low soil pH may contribute to the physiological condition known as blossom end rot, which affects tomatoes and summer squash.

Applying the proper amounts of limestone and fertilizer pro- motes healthy, productive plants. In addition, it minimizes the potential for water pollution from over-application of nutrients, especially nitrogen and phosphorus.

WHAT CAN SOIL TESTS DETERMINE?

The standard nutrient analysis will provide the soil sample’s pH and the available amounts of phosphorus, potassium, calcium, magnesium, micronutrients and an estimate of total lead. Site-specific fertilizer recommendations are provided based on the soil test results. Recommendations for modifying the soil pH with limestone or sulfur are made if necessary.

Separate analyses offered by the lab include: percent organic matter, particle size analysis (the relative amounts of sand, silt and clay), micronutrients, soilless media and soluble salts. Commercial agronomic or vegetable growers may be interested in our presidedress soil nitrate test.

WHAT CAN SOIL TESTS NOT DETERMINE?

The soil fertility test performed at UConn cannot detect the presence of contaminants such as pesticides or petroleum products. A listing of state approved environmental laboratories which can perform these analyses is available at the Connecticut Department of Public Health’s website, www.state.ct.us/dph

Our soil tests also cannot identify problems due to insects, diseases, poor or excessive drainage, environmental stresses such as drought or winter injury, or improper cultural techniques.

WHEN IS THE BEST TIME OF YEAR TO HAVE MY SOIL TESTED?

A soil sample can be collected any time the ground is not frozen. The lab performs soil analyses year round. Fall is an optimal time for sampling because added amendments can begin to react with the soil over the winter. When submitting samples in the springtime, try to send them in early enough to give yourself time to prepare your beds before planting. Generally, the turnover time is 3 to 5 days in the lab but may be longer in April and May.

A soil test every 3 to 5 years is adequate for most situations. An exception to this would be sites requiring large nutrient additions or pH adjustments. In this case, it would be advisable to test one year after the recommendations for limestone and/or fertilizer were followed to monitor their effect. Whenever comparisons of results are desired, take samples at the same time of year.

# Soil Testing

By Dawn Pettinelli – Extension Instructor Plant Science & Landscape Architecture
Saves Money & The Environment!

A soil test is an inexpensive and valuable tool to help determine what will grow best in your soil, and what it might need to boost its fertility. It’s a smart decision to test the soil every three to five years and it’s particularly important in new garden areas or in established plantings that are not performing as well as expected. Soil testing eliminates the guesswork many gardeners face when deciding the kinds and amounts of fertilizers or soil amendments they should be using.

Get Professional Soil Recommendations

Growing a garden or a lawn? A soil test is both environmentally and financially sensible, and costs around $10 from the UConn soil lab. • Why test your soil? Knowing how much fertilizer, limestone or any ammendment to apply saves time and money. Also it minimizes the potential for ground and surface water pollution from the overapplication of nutrents like nitrogen and phosphorous. Regardless of whether you garden organically or use synthetic fertilizers, you will find that plants grow best when their nutritional requirements are met. This is achieved not only by the addition of nutrients such as nitrogen, phosphorus and potassium but also by sometimes modifying the soil’s pH by adding limestone or sulfur. • What can a soil test determine? Test results indicate the soil’s pH level, the amounts of available plant nutrients such as phosphorus, potassium, calcium, magnesium, micronutrients and any nutrient imbalances, excesses or deficiencies. Soil pH is a measurement of the acidity of the soil. A pH of 7.0 is neutral, below 7.0 is acidic, and above 7.0 is alkaline. Tests also will report the amount of estmated total lead in the soil…a contaminant that must be dealth with. Site specific fertilizer recommendations are provided based on the soil test results. Separate analyses offered by the lab include: percent organic matter, soil texture determination, and soluble salts. • What can a soil test not determine? The soil fertility test performed at the University of Connecticut cannot detect the presence of contaminants such as pesticides or petroleum products, problems due to insects, diseases, poor or excessive drainage, environmental stresses such as drought or winter injury, or improper cultural techniques. A listing of state approved environmental laboratories that can perform these analyses is available at the Connecticut Department of Public Health’s website. • When is the best time of year to have your soil tested? Fall is the best time for sampling because what you add to the soil then can begin to react with the soil over the winter. When submitting samples in the spring, try to send them in early enough to give yourself time to prepare your beds before planting. Generally, the turnover time is 3 to 5 days in the lab but may be up to two weeks in April and May. If you want to compare your results to previous soil test results, take your samples at the same time of year. • How do you get your soil tested? Directions for sample collection, fees and mailing directions are listed in our free soil testing information brochure that is available at your local Cooperative Extension Center, at the UConn Home and Garden Education Center, toll-free (877) 486-6271, at some Connecticut garden centers, or by calling the UConn Soil Nutrient Analysis Laboratory at (860) 486-4274. You can also visit UConn’s soil test web site. Those preferring the convenience of our prepaid soil test collection kit can contact the lab or stop by a local Extension Center. Soils in the prepaid kits receive the standard nutrient analysis and currently cost just$8.00. Postage is not included in the cost of the kit but usually costs around than \$2 per sample. The lab can usually get you your results in about ten days!

# Soil Testing at UConn

The University of Connecticut Soil Nutrient Analysis Laboratory (SNAL) has been serving the farmers, greenhouse growers and residents of Connecticut for over 50 years. Currently, it is directed by Dr. Thomas Morris and managed by Dawn Pettinelli; Deborah Tyser is our full-time laboratory technician.

Our Goals

The Soil Nutrient Analysis Laboratory has three major objectives. First is to provide an inexpensive means for both agricultural producers and home owners to test their soil fertility and receive environmentally sound limestone and fertilizer recommendations. The second major focus of the Laboratory is education. Through our analyses as well as outreach efforts, clients and the public are being informed about wise soil management and fertility practices. The Laboratory also analyses research samples for University faculty and graduate students and serves as a teaching laboratory for several Department of Plant Science classes.

Soil Analysis

The laboratory processes about 14,000 soil samples annually. Samples are routinely tested for a variety of major and minor plant nutrients, lead and pH. Limestone and fertilizer recommendations are based on University research and field studies. Plants grown under optimum soil pH and fertility levels typically are healthier and more vigorous. Applications of limestone or fertilizer in inadequate or excessive amounts, wastes both time and money, can cause plants to perform poorly and, in the case of excessive fertilizer use, can negatively impact our surface and ground water supplies.

Nitrogen Testing

In addition to routine soil fertility testing, the SNAL also offers commercial agronomic and commercial vegetable growers the Pre-sidedress Soil Nitrate Test (PSNT). From June 1st through August 15th, soil samples are analyzed for nitrate-nitrogen on a 24 hour turnover. As a companion to the PSNT, our laboratory performs the End-of-Season Cornstalk Nitrate Test after harvest.