Healthy soil is the stuff that allows us to grow lush fruits, crispy greens, and fragrant flowers and herbs. Without healthy soil, very little will grow. Soil is the Earth’s living skin.
To call someone ‘dirty’ is usually an insult, and there are many other soil slurs that demonstrate our careless attitude toward something so important, but the Dust Bowl of the 1930s was a harsh lesson in the importance of caring for and protecting this valuable resource.
Soil stores water and nutrients, filters water, helps break down toxic wastes, and is a critical player in carbon cycling, nitrogen cycling, and, let’s face it, life on Earth.
So what is soil?
Many people assume that soil is simply ground up rocks, but this is only partly true. Soil is made up of organic matter (1-5%), minerals (45-49%), water (25%) and air (25%). Organic matter (humus) includes living things and the remains of things that used to be alive. The water and air that make life possible are found in the spaces (macropores and micropores) between chunks of organic material and minerals, called soil aggregates. The minerals are normally the ground up bits of local bedrock. Depending on how small the pieces are, they are called sand, silt, or clay. Obviously, you can see a grain of sand with the naked eye. A particle of silt can be seen with a standard microscope, but a particle of clay, being smaller than most bacteria, can only be seen using an electron microscope - clay is that small! There are 12 types (orders) of soil, depending on color, texture, mineral content, and structure.
Soil surface area
The surface of soil particles is where the magic happens. This is where the chemical reactions needed to move nutrients from the soil into plant roots takes place. Clay has 100,000 times the amount of surface area as an equal weight of sand. Sand is chemically inactive when compared to clay. The spaces between the particles is important, too. Being physically larger, sand particles have fewer, bigger spaces, allowing nutrients and water to leach out. Being the smallest, clay particles have many more, very tiny spaces. These spaces hold up to six times more water and nutrients, but the water moves more slowly and is harder for plant roots to access. Loam is considered the ideal growth medium for most plants. Loam consists of 40% sand, 40% silt, and 20% clay.
Types of soil
Soil texture is a function of the proportion of sand, silt, and clay it contains. Use these steps to determine your soil texture:
Then, use the chart below to find where the three percentages meet to identify your soil type:
For example, a 10” jar has 1” sand (10%), 7” silt (70%) and 2” (20%) clay:
The way soil particles are held together into aggregates is called soil structure. Soil structure impacts porosity and permeability, water-holding capacity, and nutrient availability. Soil structure problems, such as compaction and crusting, can prevent roots from getting where they need to go. Good soil structure can help move water away from roots when over-watering occurs. Ideally, your soil should be made up of various sized bits that hold their shape under slight pressure. Follow these steps to determine your soil structure:
The color of your soil can tell you a lot about what it contains. Darker soil tends to hold more organic matter. Soils with red, yellow, or brown tints contain iron oxides. Yellow soil may also indicate a drainage problem. White soil contains gypsum, carbonates, and other salts. Blue-green and gray soils indicate continuous exposure to water, which can cause problems for most garden plants.
Soil texture and structure may be ideal, but if the soil pH is incorrect for the plants being grown, they will be unable to absorb the nutrients they need. Most plants prefer a pH of 6.0 to 6.5 to thrive.
How to create healthy soil
Healthy soil needs organic material to promote good structure, proper drainage, and nutrient and water flow. Soil creation is called pedogenesis. [Did you know that soil, water, air, and all living things make up the Earth’s pedosphere?]
Use these tips to improve your soil:
You can grow a surprising amount of food in your own yard. Ask me how!