How does the soil composition inform our management decisions?
Background: Measuring the Makeup of Your Soil
Traditionally, soil is categorized by percentages of non-organic particles in the forms of sand, silt, and clay. These three materials form the texture of the soil, differing in terms of granularity (sand has the largest particle sizes, while clay has the smallest) and their emergent properties such as porosity (and water storing ability), aeration, ability to hold organic content, compaction, ability to resist erosion, and resistance to changes in pH, among others. The percent makeup of one’s soil, then, is an important matter for identifying crop growing potential as well as possible challenges. Luckily, estimating the composition of soil can be done relatively easily! With a few steps and observations, you can know in which direction you must “push” your garden to achieve an ideal soil texture.
Students will be able to...
Measure the general makeup of soil in their garden, farm, or yard
Use soil composition to make decisions on what to plant and how to improve and care for soil
clay /klā/ noun. - a type of soil particle with a very fine granularity (less than 0.002 mm in diameter)
loam /lōm/ noun. - a type of soil that has larger proportions of both sand and silt than it does of clay
sand /sand/ noun. - a type of soil particle with a coarse granularity (0.05 mm - 2 mm in diameter
silt /silt/ noun. - a type of soil particle with medium granularity [relative to sand and clay] (0.002 mm - 0.05 mm in diameter)
1. Gather your materials. You will need the following supplies:
mason jar or other clear container (1) · soil from garden/farm · shovel or trowel · water · measuring tape or ruler
2. Watch the following YouTube video to see a demonstration of how to measure the makeup of your soil. Then, follow along with the remainder of the lesson by reading the steps below.
3. In your garden, farm, or yard, choose a representative bed or parcel of land that you can easily remove some soil from. The location you choose to dig in should be an “average” looking and behaving area, qualitatively speaking -- an area that accurately approximates your entire space.
4. Dig a small hole about 6 inches (half of 1 foot) into the soil using your hand, a trowel, or a shovel, and fill your mason jar about ¾ full with the contents you remove from the ground. The soil put into the jar should have about equal parts of each 1-inch layer of soil for a representative sample.
5. Fill the mason jar to the top with water, secure the lid on the jar, and shake the jar to mix the contents (at least 2 minutes). After the jar has been shaken, let it sit for 1 minute, and observe any separation taking place. Let it sit for another 4 minutes, and observe again. You should see distinct layers beginning to form. Let it sit for an hour, and observe it again. You may begin to see 5 layers at this point, with the most dense layers on the bottom. Let the jar sit for 24 hours, and use your tape measure to determine the exact texture content of your soil by measuring the thickness of each layer. The layers may be difficult to tell apart, but see if you can notice subtle color differences and size differences.
⚛ Most Dense → Least Dense… Bottom → Top
Sand → Silt → Clay → Water → Residual organic matter
✋ What’s the proper texture? … Generally, in order to maximize the traits of each particle size, gardeners aim for proportions of sand, silt, and clay that form what is called a “loam.” 40% sand, 40% silt, and 20% clay are often considered the ideal ratios. Ask yourself the questions below to help you imagine why texture variety is important:
Which particle type provides the greatest drainage? (Hint: the larger the particle size, the more water that is allowed to pass through)
Which soil particle compacts most easily? (Hint: the smaller the particle size, the easier spaces fill)
Which soil particle can be blown away by wind most easily? (Hint: if the particle is fine, it has a small weight which makes it susceptible to being carried off by wind; on the other hand, if the particle is very coarse, it has a large surface area which can cause it to be swept up by wind)
Download the PDF version of this lesson plan: