Soil Science
Below are resources to teach about the soil in Houston.
Overview
One of the most overlooked natural resources is literally right beneath our feet. Considered the living skin of our planet, soil is made of rocks, decayed plants and animal matter, air, and water. Soil plays an essential role in sustaining plant and animal life, nutrient cycling, water management, pollutant filtration, and providing support to vegetation and human structures.
Here in Houston, we have many different and unique soils depending upon where you are in the region and how close you are to the water. In some places, our soils are contaminated with toxic chemicals and in other places, our soils are depleted from years of heavy agriculture.
Pedology is the study of soil, and there are a multitude of commercial, governmental and nonprofit agencies in Houston that deal with soil science.
How is Soil Made?
Through the process of weathering, large rocks break down into smaller pieces eventually becoming a part of soil. This process is slow and can take hundreds of years. Wind, water, and extreme temperatures cause rock to break down over time. The size of these rocks and ratio of various rock sizes plays a large role in determining the soil structure.
Soil is not just tiny rocks; it is also made of decayed plants and animal matter called humus. Humus is made from things that were once alive, that then decay and become part of the soil, giving it nutrients and a darker color.
Soil Types and Properties
How soil looks and feels tells us about its properties. There are three types of soil: sand, silt and clay. The difference between soil types is the size of the rock particles.
The largest soil type is sand; it feels rough and gritty. There are air spaces between the grains of sand which allow for water to drain quickly. This makes plant growth difficult with such easily drained soil.
Silt has medium size particles and feels smooth when wet. Silt holds on to more water than sand and does not drain as quickly.
Clay has the smallest sized particles. It feels sticky when wet and hard when dry. The small rock particles packed tightly together, holding the most water; however, there is little space for air which makes plant growth more difficult.
The ideal type of soil for growing most plants is called loam. Loam is a mixture of clay, silt, sand, and humus which provides air, water, and nutrients to the roots.
The Texas Almanac expresses that Texas soils are complex due to the wide diversity of climate, vegetation, geology, and landscape across the state. There are more than 1,300 different soil types recognized in Texas, with each having a specific set of properties that affects its use.
Soil types can be generalized into orders. Dominant soil orders of Texas line up well with land resource areas, or ecoregions, across the state. See Soils of Texas and The Twelve Orders of Soil Taxonomy | Natural Resources Conservation Service for more details. There’s also a Texas Soil Characterization database through Texas A&M University.
Greater Houston Soils
According to Houston Wilderness, the Greater Houston region comprises primarily two major soil types: Vertisols and Alfisols.
Alfisols contain topsoil and up to 20-40 inches of sandy loam (sand mixed with clay) before reaching a clay pan. These soils typically form under grassland vegetation. Surface runoff is slow to very slow, permeability is very slow, and the available water holding capacity is high due to high clay content at depth.
Vertisols are clay-rich soils (40-75% clay content) that shrink when dry, swell when wet, and consist of topsoil sitting atop a deep clay pan. When dry, vertisols form large cracks that may be more than three feet deep and several inches wide. Vertisols typically form under grassland vegetation and are self-mulching, highly fertile soils due to their high clay content.
Soil type can be narrowed down to more specific parameters. Find out what your exact soil type is by using USDA NRCS Web Soil Survey.
ENVIRONMENTAL JUSTICE
In many areas of Houston, industry has left soils in a state of peril. For example, in Houston’s Fifth Ward and Kashmere Gardens, dioxin levels in the neighborhood’s soils exceed the U.S. Environmental Protection Agency’s threshold for children. Learn more in this article from the Texas Tribune in 2022.
Catastrophic flooding of industrial sites, more likely as a result of climate change and increased strength and quantity of tropical storms, threatens to transport once-sequestered chemicals into nearby residential areas. In this report from Dr. Thomas Marlow, et.al, they warn that “in Harris County, there are 15 state and federally recognized superfund sites identified by the Government Accountability Office as being at risk of future flooding (GAO 2019). And there are 1985 relic industrial sites in the county at elevated flood risk.” Urban flooding will spread hazardous waste and contaminate soils for thousands of people, especially in socially vulnerable communities.
Local Resources
To get soil tested for contamination in Houston, you can consider the following options:
1. Texas Commission on Environmental Quality (TCEQ): The TCEQ provides resources and information on soil testing and environmental assessments. They can guide you through proper testing procedures and may offer lists of certified laboratories in the area.
2. Harris County Soil and Water Conservation District: They may provide information on soil testing services or direct you to appropriate resources.
3. Texas A&M AgriLife Extension: They offer soil testing services primarily for agricultural purposes but can provide guidance on soil quality and potential contamination.
4. Private Environmental Testing Laboratory or Local Environmental Consultants: Environmental consulting firms in Houston and laboratories often provide soil testing services. They can assess your specific needs and guide you through the testing process.
Before proceeding with soil testing, it's a good idea to contact the relevant organization or laboratory to discuss your specific needs, obtain cost estimates, and ensure that the testing methods align with your objectives.
Activities/Lessons
Explore various K-12 Soil Science activities and curriculums for teachers and educators by visiting Soil Society of America’s Soils4Teachers website.
Check out various soil experiments and hands-on projects for kids by visiting Soil Society of America’s Soils4Kids website.