The soil is a reservoir that holds water for plants. It is important for recharging groundwater by allowing rainfall to infiltrate and filter through the soil into the water table. This happens because the soil is a porous media where the spaces in the soil (pores) are either filled with air or water. The capacity of soil to hold water determines your watering practices in order to provide continued sufficient water for plant growth depending on the drought resistance of your plants. However, not all soils are equal in this capacity.

Bare soil dark with organic matter. Photo by dmp2022.

Field capacity is an important characteristic of soil because it represents the maximum amount of water that a soil can hold. The main soil properties that affect the field capacity of a soil include soil texture, organic matter and compaction.

Soil texture refers to the proportions of sand (0.05-2.0 mm), silt (0.002-0.05 mm), and clay (smaller than 0.002 mm) in the soil. A higher proportion of the larger sand size particles, the more coarse a soil is. Sandy, coarse textured soils have lower field capacity. This is because the greater amount of large particles leads to larger pores from which the water can quickly drain. On the other hand, fine textured soils comprised of the smaller soil particles have a greater amount of small pores that can hold water better, leading to a greater water holding capacity of these soils. However, not all the water held by soils can be used by plants. Some water is very tightly held in the soil and not able to be taken up by plants.

Figure shows general relationship between soil how plant available water capacity (easily available water plus slowly available water) is impacted by soil texture (source: The Nature and Properties of Soils by Ray R. Weil and Nyle C. Brady).

Plant available water holding capacity represents the water retained in soil between field capacity and the wilting point, in another word, it represents the amount of water retained in soil that can be taken up by plants. Even though soils that have high clay contents (such as clay loam, clay) can hold more water, they hold the water tightly so less water is available for plants than silt loam or a sandy loam. The question is, how do we improve soil texture for improved plant available water holding capacity? Unfortunately, changing soil texture of a field is not a viable option unless you introduce foreign soils to the field. Fortunately, there are other options available to improve plant available water holding capacity.

Organic matter is another portion of the soil that holds water. The higher the organic matter content, the more water the soil can hold. Increasing organic matter can increase the field capacity significantly. Increased soil organic matter content improves soil structure which results in increased infiltration, therefore, increasing plant available water. The strategies to increase soil organic matter includes growing cover crops, adding manure, compost or biochar or mixing in leaf mold, peat moss or coir. Avoid disturbing the soil by refraining from overtilling, either manually or with a rototiller.

Till either manually or with a rototiller only when necessary. Photo by dmp2012

Compaction reduces the plant available water holding capacity of a soil. This is because compaction reduces porosity which in turn decreases a soil’s field capacity. Compaction also crushes large pores into smaller pores which leads to a greater proportion of the water being held more tightly by soils. As a result, compaction results in less water available for plants to take up. Also, when a soil is compacted, it becomes harder for roots to penetrate. This can lead to less volume of soil for roots to access to water that is held below than the compacted layer. Stay off soils when they are wet, avoid overtilling, and make defined walking paths through garden areas or perhaps use stepping stones so as not to compact your soils.

Salt content is another soil characteristic that impacts availability of water to plants. Soils that are high in salt concentration tend to have higher wilting points that results in less water for plants to take up. This is more of a problem in the dry regions of the US where salt accumulation is mainly a result of natural soil formation processes and irrigation. In our soils, the salt level can be elevated in areas that have been overfertilized.

In addition to adopting practices that can increase the plant available water holding capacity, there are other practical options for reducing water loss from soil. Mulching is an effective practice to reduce evaporation loss of water. There are many sources of mulches available in the market such as hay, straw, wood chips, bark or cocoa shells. Gardeners can also use untreated lawn clippings.

Haiying Tao, Ph. D.

This past Saturday I was fortunate to be a part of the CT Envirothon Soils Workshop team coordinated by State Soil Scientist, Deb Surabian, from the USDA Natural Resources Conservation Service (NRCS). Our mission was to share our soil science knowledge with the high school students and their teachers or advisors enrolled in the CT Envirothon program. Students gain an appreciation and understanding for the vital ecosystem roles soils play and learn how to classify and describe them. They will then go on and use this knowledge for the annual State Envirothon Competition to be held May 16, 2019.


CT Envirothon Banner. Photo by dmp.

For those unfamiliar with the Envirothon, it was first conceived in the late 70s in Pennsylvania by the state’s Conservation Districts. They believed in the importance of a statewide environmental program aimed at high school students and focused on key natural resources including soils, aquatics, forestry and wildlife. Within a few years, Massachusetts, Maine, New York and Ohio had started Envirothon programs and the first National Envirothon Competition was held in 1988 in Pennsylvania. By the time 2000 came along, more than 40 states as well as several Canadian provinces were competing in the national contest.

Connecticut’s first statewide competition was held in 1992 and 15 schools participated. That number climbed to 46 schools in 2000 and over the past 2 years there was about 25 schools competing. Several high schools have multiple teams, however. The CT Envirothon is open to public, private, vocational and home-schooled students.

Soil pit 2018 Topsmead St Forest 2

Envirothon participants describing soil pit at 2018 CT State Envirothon Competition at Topsmead State Forest. Photo by dmp, 2018

Typically, a high school teacher, advisor or other student advocate will gather a team of 5 environmentally enthused students (plus 2 alternates). Once registered in the CT Envirothon, teams will receive study guides, curriculum materials and notice of the 4 training sessions – one on each of the natural resources areas of interest mentioned above. These training workshops are presented by professionals in their respective fields including soil scientists, wildlife ecologists, aquatics biologists, foresters and others. Both students and teachers benefit by interacting with these professionals by gaining knowledge, networking and exploring career opportunities in the natural resources fields. Students keep us professionals current (and on our toes!) and truly it is invigorating to feel that the time we take to share our knowledge is valued and will be put to good use.

The CT State Envirothon Competition is held each May in varied locations throughout the state. Teams compete in all 4 natural resources areas plus in a short oral presentation on the year’s current issue. This year’s current issue is ‘Agriculture and the Environment, Knowledge and Technology to Feed the World’. After morning competition, all gather for a luncheon cookout and then the award ceremony. Winners are announced in each of the 5 categories as well as the overall winning team who will go on to represent Connecticut in the national North American Envirothon. The winners will go up against approximately 60 teams from the U.S. and Canada and the 2019 competition will take place in Raleigh, North Carolina from July 28th through August 2nd.

This year’s Soils Workshop was held at the Tolland Agricultural Center in Vernon and consisted of 4 hands-on stations plus a presentation by USDA NRCS Soil Conservationist, Bill Purcell. Bill tackled the current issue and talked about the importance of soil health in agricultural systems and management practices like no-till, cover cropping and conservation tillage that keep our farmland soils healthy and productive.

Bill Purcell

USDA NRCS Soil Conservationist, Bill Purcell. Photo by dmp 2018

Deb Surabian was charged with familiarizing students with map reading and interpreting soil data. In recent years, the old soil survey manuals were converted into an electronic Web Soil Survey. According to the USDA NRCS, it provides access to the largest natural resource information system in the work with soil maps and corresponding data available for 95% of the counties in the U.S. at this time with a soon to be reached goal of 100%. After selecting your ‘area of interest’, one can find out information about what soil series are present in the area, their characteristics, land use suitability and more. And, there’s an App for that – free for Android or iPhones.

Deb Surabian, CT state soil scientist

Deb Surabian, USDA NRCS State Soil Scientist CT/RI demonstrating how to use the web soil survey. Photo by Jean Laughman

Retired USDA NRCS Resource Soil Scientist, Lisa Krall along with Bill Purcell brought examples of soils from both well and poorly managed fields so students could examine the difference in structure and erodibility. They created mini soil filtration systems that showed how differences in vegetative cover impact soil erosion. Many may not be aware that half the Earth’s topsoil has been lost over the past 150 years. With an ever increasing population, how will we feed ourselves without taking care of our soils? All life is dependent on the soil.

Lisa Krall & Bill Purcell soil health

Retired USDA NRCS Resource Soil Scientist, Lisa Krall & USDA NRCS Soil Conservationist, Bill Purcell exploring soil health with students. Photo by Jean Laughman

The original plan was for Jacob Isleib, USDA NRCS Soil Scientist to lead the students in a hands-on soil description in one of the soil pits on the TAC property. Because of the heavy rainfall we were experiencing this past weekend, he had to use trays of soil and soil monoliths as well as some Powerpoint illustrations, to show the students how to describe and categorize a soil. Students learned how to designate soil horizons and ascertain soil properties in order to evaluate the position of that soil series in the landscape and be able to interpret potential uses as well as limitations.

Jacob Isleib

USDA NRCS Soil Scientist, Jacob Isleib teaching Envirothon participants how to describe soils using monoliths. Photo by Jean Laughman

And me, as a UConn Assistant Extension Educator as well as a soil scientist, worked with students to practice how to assign soils colors using the Munsell Color System as well as how to hand-texture a soil. During the competitions, students will be shown a soil in a previously dug pit and need to be able to delineate the horizons and characterize them by texture and color among other properties. There are 12 textural classes according to the USDA textural triangle. The students’ favorite soil to texture is the silty clay loam because as the name implies it contains clay and therefore is moldable. It is also sticky and I lose a lot of this soil at every workshop as it sticks to everyones’ hands and ends up running down the drainpipes. Fortunately, the UConn Soil Lab, which I manage, recently received dozens of Puerto Rican soils which are mostly silty clay and clay loams so for now, the clay loam coffers are full. While many people believe they have clay soils, realistically in Connecticut they are rather rare. What people really have most of the times are compacted soils.

Dawn soil texture 2

Dawn Pettinelli reviewing how to hand texture soil. Photo by Jean Laughman

Another topic I cover is invasive earthworms. While there are no native earthworms in Connecticut as they were all wiped out by the glacier fifteen thousand or more years ago, the more recent introduction of Asian species of earthworms is a significant problem both in home gardens and forested ecosystems. Not that we can even control the invasives that are highly visible like purple loosestrife and bittersweet but students and their advisors need to know that any time a non-native species is introduced into a native ecosystem, there are consequences.


Crazy snake worm (Amynthas spp). Photo by dmp, 2018

It has been a decade since I was first invited to assist the USDA NRCS soil scientist crew with the CT Envirothon Soils Workshop. While I sometimes grumble at the early hour I need to arise on a Saturday, at the end of the day I am a happy, and sometimes humbled participant, in an effort to pass the soils torch on to the next generation of environmental professionals.

Dawn P.

This past weekend, I was invited to participate in the 2014 Great Park Pursuit Finale. For those who are not familiar with the Great Park Pursuit, it is part of the No Child Left Inside program launched by the Connecticut Department of Energy and the Environment ( in 2006. According to CT DEEP, “No Child Left Inside® is a promise to introduce children to the wonder of nature – for their own health and well-being, for the future of environmental conservation, and for the preservation of the beauty, character and communities of the great State of Connecticut.”

In a nutshell, families and friends register for the Great Park Pursuit in April and for 7 consecutive weekends in May and June, meet at certain parks and state forests throughout the state for recreational opportunities and educational activities. If all events are attended and other prerequisites, like photos, submitted, families can receive state park season passes at the final event, which this year was held at UConn on June 21st.

So I was trying to come up with a hand’s on soil activity that would be suitable for young children, would not require lugging massive quantities of soil and would not be too ‘dirty’. One of the soils professors at UConn, Cristian Schulthess, had shown me some soil paintings that a few of his students had done as a class assignment and I remember how beautiful they were. He gave me instructions on making the paints and I started collecting soils to use.

Soil painting by Chelsey Putera, UConn student 2006

Soil painting by Chelsey Putera, UConn student 2006

The colors of soil are derived from both the minerals that make up the soil as well as organic materials in the soil. For instance the red soils in Connecticut are due to iron in an oxidized form – think rusty nail.

The next step took the longest – using a mortar and pestle to crush the soils and then putting them through a fine sieve. The directions said to put them through pantyhose but I wasn’t going to ruin a perfectly good pair of stockings! That gives you an idea though of how fine the soil needs to be.

Preparing soils for painting

Preparing soils for painting

To turn the soil into a medium for painting, it was mixed in small plastic cups with clear artist’s acrylic and thinned with a little water. I ended up using watercolor paper which was cut in half for the kids to paint on as regular copy paper got too wet and tore. Last Saturday was a beautiful day but a bit breezy for soil painting outdoors so I just made a lot of small batches so they would not dry out too fast!

GPP UConn Soil Painting, Photo by CT DEEP 2014

GPP UConn Soil Painting, Photo by CT DEEP 2014

All in all, 175 kids plus a few grown-ups came to the table to try their hand at soil painting. Not a bad turn out and hopefully a lesson that soil has many uses and we should appreciate all of them!

GPP UConn Soil Painting, Photo by CT DEEP 2014

GPP UConn Soil Painting, Photo by CT DEEP 2014

Good Gardening!

Dawn P.