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 (a_H+)

(a_H+ = 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”.

(Image from: http://www.edu.pe.ca/gulfshore/Archives/ACIDSBAS/scipage.htm)

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.

(Image from: http://www.pda.org.uk/pda_leaflets/24-soil-analysis-key-to-nutrient-management-planning/)

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 list of 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!

Joe C.

 

A Visit to the Bahamas

When my husband and I headed to Boston to board the Norwegian Dawn to the beautiful island of Bermuda we were very excited. The first item on our list of things to do while on the island was to visit the Bermuda Botanical Gardens. Having kept an eye on the weather reports we knew that Hurricane Gonzalo could make landfall on Bermuda on Friday the 17^th of October. We were not scheduled to get there until Sunday, the 19^th, and ever the optimists, felt that we would still be able to dock in King’s Wharf. We even discussed going to the Botanical Garden to help with any clean-up that was needed after the storm.

The hurricane made a direct hit on Bermuda causing $200 million in damage and leaving 90% of the island without electricity. As such, the cruise ship would not be able to dock there. We were then redirected to Nassau, Bahamas and Great Stirrup Cay. Off we went to the ship’s library to look up information on the Bahamas. I was very happy to discover that there is a Botanical Garden in Nassau and that across the road from that is the Ardastra Gardens and Zoo. The day that we docked in Nassau we jumped on a city bus and headed for the Botanical Garden, ready to get some amazing pictures. Once again, it was not to be. There had been a big food festival on the grounds of the Botanical Garden over the weekend and it was closed so that they could clean up. Ok, a deep breath and then a walk across the street to the Ardastra Gardens and Zoo. It did not have an amazing array of flowers but there were several tropical varieties that were new to us.

Epiphytic orchids at the Ardastra gardens

Epiphytic Orchids

It was very interesting to see the orchids that were growing on the sides of the trees. Known as an epiphyte, these orchids are not parasitic to their host plant. Their roots are used primarily for support and for attachment to the host plant. As autotrophs, they derive their nutrients and moisture from the air, the rain, and the debris that collects around their base. They use available sunlight for the process of photosynthesis. In turn, they provide a habitat for animals, fungi, and bacteria. Epiphytes can also create a cooler and moister environment in the host plant canopy to the benefit of the host plant. Many other familiar plants also in the epiphytic category include mosses, ferns, lichens, algae, cacti, and bromeliads.

Ferns growing in the limestone at Fort Fincastle

Plants growing in the limestone

And while these species of ferns and plants are not epiphytic, we found them growing in the cracks in the limestone walls of Fort Fincastle, Nassau. We also saw many plants that had adapted themselves to grow in the sandy, rocky areas of the beaches. These plants can greatly reduce the damage that can be caused by wind or water erosion.

Great Stirrip Cay

Although we didn’t get to visit our first or second choices, we still saw some beautiful and interesting things. And we even got to see the trained marching flamingos at the Ardastra Zoo!

The marching flamingos!

Susan Pelton