What Determines the Texture of Soil?

If you’re a proud homeowner or professional gardener, we’re sure you already know a thing or two about the importance of soil texture and its ability to influence soil/water relationships, plant nutrition, and gas exchange.  

Soil texture is determined by the percentage of silt, clay, and sand present within the soil. Depending on the size of these particles, the texture of the soil will let us know the water and oxygen-holding capabilities, as well as the rate at which water can enter and pass through the soil structure. 

Accurately determining soil texture in a lab is time-consuming and costly, therefore, it’s often necessary to make an educated judgment on soil texture by feel, which can be accurate if done correctly.

In this article, we will be discussing the importance of soil texture and the different methods you can take to determine it for yourself.

The Three Building Blocks of Soil

The three building blocks of soil are as follows: sand, silt, and clay.

Each type of substance feel very different to the touch and lend different benefits to the soil. 

Though three types of soil particles are differentiated by their size, which is a physical property, it is the relative amount of each of these components has the largest influence on the physical, chemical, and biological properties of soil.

For reference, here is a table below with further information on particle size:

Soil Particle Type

Diameter (mm)

Clay

<0.002

Silt

0.002 to 0.05

Sand

0.05 to 2.0

The pore gaps that exist between soil particles are the most influential factor responsible for the amount of water that soil will be able to hold.

For instance, finer soil textures have a larger surface area, smaller pores, and a slower water infiltration into the soil structure than coarser soil textures. Here’s a breakdown of the three main components:

Sand

This is the largest soil particle. It measures from 0.05 to 2 mm in diameter and can be seen via the human eye without the need for a magnifying instrument.

Sand feels gritty and dry and has the lowest water-holding capabilities out of all the soil components.  

Silt

This is the medium-sized component in soil, and measures 0.002 to 0.05 mm in diameter. When silt is dry, the particles will have a similar texture to baby powder or another type of finely milled powder. However, when wet, the silt will feel very silky and smooth.

Though silt is visible to the naked eye, it is not as easy to spot as sand, so you might need glasses or a magnifying tool. Out of the three kinds of components, silt is able to hold a moderate amount of water.

Clay

Clay particles are the smallest and measure less than 0.002 mm in diameter. and can only be seen with powerful microscopes.

Fun fact:  the biggest clay particle is around 25 times smaller than the largest silt particle and a 1000 times smaller than the largest sand particle! To touch, clay will feel sticky when wet and brittle when dry.

Out of the three main components, clay can hold much more water than sand or silt.

How are soil textures categorized? 

Generally, soils are carefully divided into three categorical texture groups. These are:

  • Coarse-textured soils
  • Medium-textured soils
  • Fine-textured soils 

A coarse-textured or ‘sandy’ soil is made up of 70 to 100 percent of sand-sized particles.

Clay and silt may be present in coarse-textured soil, but these two components will only make up to around 30%, if any.

As clay displays strong properties, a soil only needs to have 35 to 40 percent clay-sized particles to be considered fine-textured or ‘clayey’ soil and, medium-textured soils are the kind that has an even distribution between clay, silt sand particles.

Generally, a coarse-textured soil has a low water-holding capacity, higher water infiltration rates, low nutrient retention, and responds well to supplemental irrigation.

On the other hand, fine-textured soils are able to remain wet for much longer than medium- or coarse-textured soils, have slower water infiltration rates, and higher nutrient retention. 

In contrast, medium-texture soils, such as clay loams or silt loams, have a good balance of sand silt, and clay. They are generally very productive soils that allow for sufficient water infiltration without excessive drainage and have good water holding capacity and nutrient retention. This makes medium-textured soils the most popular for use in agriculture. 

If taken to a laboratory,  a sample of soil would be examined in order to determine the relative amount of sand, silt, and clay particles present, and then making an accurate judgment based on the findings.

As an example, if the laboratory results found that the soil sample contained 70% of sand, it would be deemed as coarse-textured, ‘sandy’ soil.

However, sending off your soil to a lab is costly and can take anywhere from a few weeks to a few months to get results back, so another method available to us is to estimate soil texture by hand. 

How do I determine soil texture by hand?

Step 1: Take a small handful of soil into your hand and slowly add water a few drops of water. Mix the soil with the water and gently squeeze the ball to determine if it stays together in a putty-like mixture, or if it falls apart. 

Step 2: If the ball of soil doesn’t fall apart, gently press the ball between your thumb and index finger, and measure how long you can ‘work’ the soil out into a flat, ‘ribbon’ shape before it falls apart. 

Step 3: After completing this test, add an additional drop of water to a pinch of soil in the palm of your hand until you have a puddle and then rub the mud puddle against your palm to figure out whether it feels smooth, gritty, or both.

If you notice that the ball falls apart when you squeeze it together or that it feels gritty you can assume that the main component is sand, which will make it coarse-textured soil.

However, if you’ve noticed that the ball falls apart but that it feels gritty and smooth, you can assume that the main component of the texture is silt, which would make it medium-textured soil.

On the other hand, if the ball stays together, you are able to work it into a ribbon shape and it feels equally smooth and gritty, you can assume that the main component is clay, which will make it a finely textured soil. 

Final Thoughts

So, there you have it! We hope that this article has helped you to gain a better understanding of what determines soil texture, and how you can make an accurate estimate by hand.

Remember,  regardless of whether you want to plant some new seeds in your garden or you’re an agricultural farmer, all kinds of soil can be used to plant crops so long as it is properly cared for!

By identifying the soil texture, you will be able to properly care for the soil, which will, in turn, ensure maximum soil productivity. 

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