How to Determine the Texture of Soil | Textural Determination with the Soil Texture Pyramid
How and Why to Test Your Soil Before Planting
Are planning to open up a new gardening space? Maybe you want more information about the soil you are already using. A mason jar test and a quick reference to the soil pyramid chart can give you a lot of information about your soil.
The soil pyramid is a tool that can help you to identify the texture of your soil sample. Knowing more about your soil will help you improve it, tailor your crop choices, and dial in your irrigation practices for the most success.
Below you will learn about soil composition, how mineral ratios affect the texture of soil, and how to run a simple test to determine the percentage of sand, silt, and clay in your soil to determine its classification.
What is the Composition of Soil?
The main components of your soil can be broken down into 4 categories:
- Organic matter generally steals the spotlight when you hear folks talking about gardening. The organic matter in soil is composed of dead/decaying/decayed plants, roots, and other organisms. These particles hold moisture and nutrients to feed our plants, so their importance is quite apparent. Organic matter is a vital component of soil, but it generally makes up only 2-10% of the overall composition.
- Minerals comprise 40-48% of soils and are composed of sand, silt, and clay. Minerals give the soil its structure and determine water infiltration and drainage.
- Air accounts for roughly 25% -30% of soil.
- Water also makes up 25%-30% of soil.
How to Classify Soil Texture
Soil is classified by the ratios of the mineral makeup of the soil. These minerals are broken down by particle size.
Sand is made up of the largest particles (.05mm-2mm), allows rapid infiltration and drainage, making it challenging to keep plants hydrated.
Silt, whose particles range from (0.002mm-0.05mm), retains some drainage and can be suspended in water (usually deposited by moving water or runoff). Silt is incredibly susceptible to erosion by both wind and water.
Clay comprises the smallest particles in our soil, less than 0.002mm. Clay does not drain well, if at all. The particles' tiny size does not leave much room for air or water to pass through them. This is why clay is used as a liner for ponds or sealing well casings, as water infiltration would be destructive in these applications. Clay soils turn hard as rock when allowed to dry completely. This creates a layer that is nearly impenetrable for sprouting seeds. At completely dry clay is also notoriously difficult to hydrate and soften.
How do you test soil texture with a jar?
One simple test that I like to do myself is a simple jar test. This will only require a suitable jar and enough clean water. While any jar will do, it MUST hold water and be clear. The first step is taking a sample of the soil you want to check. I recommend filling the jar roughly halfway with soil. Follow this step by filling the remaining space in the jar with water. Shake your sample well and let it sit for at least a couple of hours.
As the soil settles out in the water, you will notice the soil particles start to settle into distinct layers. These are your sand, silt, and clay settling out according to the size of their particles. You may also notice some floating particles. These are going to be the organic matter portion of your soil. You can now take a ruler or tape measure and accurately measure the thickness of these layers. These measurements can be used to find the ratios of sand, silt, and clay in your soil sample with a fair amount of accuracy.
This mason jar soil test can give you a great starting point regarding your expectations of what crops a particular site will support. Some crops prefer more or less drainage. You may need to water more frequently (sandy soil) or mulch to prevent your soil from becoming a brick wall for delicate roots (clay soils).
Easy Way to Test your Soil with a Soil Jar Test
- Fill a mason jar or other clear container halfway full with a soil sample.
- Fill the remaining jar space with clean water and add a lid.
- Shake well.
- Let sit for 2+ hours until settling has occurred.
- Observe layers as the sand, silt, clay particles settle according to size.
- Measure thickness of layers.
- Calculate the ratios.
- Use numbers to determine texture classification on the soil pyramid. (below)
Understanding the Soil Pyramid
The Soil Pyramid is a three-sided chart arranged by particle size. Clay is up top, silt to the lower right, and the bottom left corner of the soil pyramid is sand.
There is a lot of variation in the mineral makeup of soils. Fortunately, the soil pyramid helps us determine what we are working with regarding mineral composition and its texture classification. It is a quick and straightforward way to determine what we can expect from our soil, by classifying them as one of the four soil textures.
Some crops will do better in soils with different mineral compositions, and knowing our soil mineral composition will put our expectations more in line with what we can reasonably expect from our garden.
Image Credit: USDA NRCS
Applying the Soil Pyramid to a Mason Jar Soil Test
With your jar test ratios, the soil pyramid is simple to use and readily available with a quick google search. First, find your percentage of clay on the left side of the pyramid, then follow the line to the right that correlates to that percentage. Next, head to the right side of the pyramid and find the percentage of silt in your soil, following the line that goes down and to the left of your percentage. Where that line intersects with the line from your percentage of clay, find the line that goes down and to the right from that intersection to see your percentage of sand.
Add these numbers up; they should make 100%. Where the three components match up is going to fall into a soil category. Maybe you have a perfect loam (40% silt, 40% sand, and 20% clay), but more likely, you will find something more along the lines of sandy loam, silt loam, or clay soil.
There are many different soils, but crops are as diverse as soil profiles. People have grown crops in nearly all soils and conditions for many years with far less technology and resources at their disposal than even the novice home gardener. We have the tools, and we have the knowledge in our modern world to make use of nearly all soil types.
What are the 4 soil texture types?
Soil texture is classified into four types:
- Sandy soil.
- Silt Soil.
- Clay Soil.
- Loamy Soil.
Sand, Silt, or Clay or Loam Soil Types
You may find that your soil structure is not the sought-after balanced loam, but do not despair! Some crops will thrive in soils not considered productive for other crops. Some cover crops can help you to improve your soil as well. While these may not completely change your ground in a single season, they will help you to make the most of your garden. Also, knowing your soil type is an excellent way to understand how to adjust your management techniques to maximize what you are working with.
What to Know About Sandy Soil and Your Garden
Most vegetables will do reasonably well in sandy soils. Sandy soil can allow water to drain excessively, so more frequent watering would be a requirement. Sandy soil also tends to drain straight down. If you use drip tape, your wetting pattern will be tighter to each emitter, with much less water "spreading" out and more water draining deeper into the soil profile for a narrow, deep watering. Soils with excessive drainage can also tend to leach nutrients, so we also want to make sure to water with less volume as the frequency of watering increases.
Suggestions for Planting in Silty Soil
Silt soil is incredibly prone to erosion. Both wind and water can wreak havoc on silt soils because the particles are tiny. They are not small enough to be sticky like clay. Silt soils generally have adequate drainage and retain moisture better than sand-dominated soils.
Cover crops are a wonderful way to keep silt soils in place during the off-season. Wind and runoff from winter seasons will take a toll on silt soils, so keeping them covered and anchored with a good green manure crop is a great way to ensure your soil remains in your garden.
For more information on using Cover Crops for Successful Land Management be sure to check out this article.
Understanding Clay Soil and How to Improve It for Gardening
Clay soils hold a lot of water, but when they dry out, they become very hard. This prevents seedlings from pushing up through that concrete-like crust. They are also challenging to moisten again once they have become dry and hard.
Mulching can help prevent our soils from drying out and becoming solid. Growing crops with a strong taproot like daikon radish can also help circumvent some problems seen with clays inhibiting fine root infiltration.
Cover crops are also a great way to break up hard clay soils and increase organic matter. Organic matter will help to add space in your soil profile for air and water between the extremely fine particles that make up clay soils.
Sand can be added to clay soils, and gypsum can be used to help break up clay soils if the time it takes to grow a cover crop is not amiable. These options are much quicker but will not have all the benefits a cover crop may provide.
Organic matter and microbial life are some of the benefits of a cover crop that we cannot replicate with a broadcast spreader and some gypsum or by tilling in some sand.
Is Loam the Perfect Soil Type?
Balanced loam soil is what we all dream of, but in reality, even loam soil does vary in its ratio of sand, silt, and clay. Typically a soil classified as loam is made with a balance of silt, clay and sand making it an ideal type. To achieve a more loamy soil, amending with organic matter or cover cropping is a great place to start.
Testing Soil Nutrition
Soil nutrition is more difficult to test for than composition. It requires lab equipment and meticulous soil preparation to take samples of specific nutrients and mineral elements. There are home kits and simple hacks to get an idea of what you are working with regarding soil quality and composition, but these kits are not always accurate. For more reliable results, I highly recommend having a testing laboratory do your testing.
Soil testing labs have costly equipment that specializes in highly accurate soil testing. This process is surprisingly affordable, considering the benefits and potential savings in the long run. If you are adding the wrong fertilizers or nutrients, you may be throwing money away. Some nutrients in excess can actually cause the plant to be unable to uptake others. Some plants may not produce as they should when nutrition is not appropriate for the crop or soil type.
Putting Your Soil Knowledge to Work
Now that you have obtained vital knowledge about your soil's makeup, you will be able to make better irrigation and crop choices according to your soil’s limitations.
Sandy soils are going to require shorter and more frequent irrigation events. Sandy soils also generally hold onto less nutrients so they may benefit from fertilizer or fertigation. When fertigating or fertilizing sandy soils, do consider the higher risk of fertilizer being carried down deeper into the soil profile than will be useful to your crops. Accurately getting water to each plant is more difficult in sandy soil as emitter wetting patterns are smaller.
Clay soils are going to take extra care to keep damp enough to remain soft and dry enough for plant roots to breathe. Adding organic matter to your soil, amending it for better drainage or mulching around plants will be your best options for clay soils. Mulch also will break down adding organic matter to the soil if thoroughly incorporated into the soil at the end of the season.
Silt can be easily compacted and is very prone to erosion from both wind and water. Silt’s vulnerability to erosion should be taken into consideration whether covering soil with landscape fabric or cover crops during the growing season. Keeping soil covered between seasons may be an integral part of your garden management plan in silt soils.
Resources on Soil
https://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/survey/
https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/?cid=nrcs142p2_054167
https://ccetompkins.org/gardening/home-gardening/soils-climate/healthy-soils
Written by Andy Russo | Russo Tree Farm