Understanding Common Soil Terms: Macronutrients to Mycorrhizae
Soil terms may seem overwhelming and confusing, but each one has a purpose! They help growers understand their garden’s soil. Once you know what they mean, you can use them to create the best dirt for your garden. Learn all about common soil terms here, from macronutrients to mycorrhizae.
Contents
Soil is more than just dirt! It’s full of microbes, worms, organic matter, nutrients, and mycorrhizae. Each part of the soil helps it function. You can think of the belowground like a forest—it’s a world full of partnerships between animals, plants, and microbes.
Some of these terms define how well soil drains, while others refer to the nutrients underground. A few are representative of the soil food web, a comprehensive ecosystem of animal and plant relationships.
Whether you’re studying for a test or trying to understand your soil, these common soil terms are helpful to know. Learn what they mean and how they influence soil quality so you can garden stress-free.
Macronutrients
Three of the most common soil terms you’ll hear refer to the necessary nutrients that plants need to grow: macronutrients, secondary nutrients, and micronutrients. Macronutrients also go by primary nutrients, as they’re the most important ones for healthy plant growth.
There are three main macronutrients. They are nitrogen, phosphorus, and potassium. All plants use these nutrients in some form or fashion. Nitrogen is beneficial for leafy growth, while potassium and phosphorus are essential for bloom and seed formation.
Nitrogen moves through the soil with water. As rains and snowfall occur in fall, winter, and spring, they leach soluble nitrogen from the ground. You may need to add compost or organic fertilizer annually to maintain proper nitrogen levels.
Secondary Nutrients
Plants use secondary nutrients in smaller doses than macro, or primary nutrients. They still need them; however, they use them in small doses. Soils may be deficient in secondary nutrients if plants grow in them often and if the ground hasn’t received amendments in a while.
There are three secondary nutrients: sulfur, calcium, and magnesium. Tomatoes and zucchinis exhibit blossom end rot when they don’t get enough calcium, often due to watering inconsistencies. Magnesium is important for leafy growth, while sulfur helps plants form healthy leaves, roots, and fruits.
CalMag is a common organic fertilizer that combines the three nutrients into one application. Apply it if you suspect the soil has a nutrient deficiency. If you’re unsure, try using a soil test to determine the levels in your garden.
Micronutrients
Micronutrients are the last group of elements that plants use to function. There are many different micronutrients, and they’re all necessary in tiny amounts. They are:
- Zinc (Zn)
- Iron (Fe)
- Copper (Cu)
- Manganese (Mn)
- Boron (B)
- Molybdenum (Mo)
- Chlorine (Cl)
Soils rarely require fertilizers with these nutrients, though potting soils may need them from time to time. They cause problems for plants when there are too many or too few of them.
Cation Exchange Capacity (CEC)
Cation exchange capacity (CEC) sounds like a complicated scientific term, but it represents a simple soil mechanism. Elements that hold electrical charges are called ions. They’re water-soluble, and they’re readily available to plants.
Cations are positively charged ions, and anions are negatively charged ions. Ions are nutrients that plants need to thrive, like potassium, calcium, and magnesium.
The more negative ions a soil can hold, the more cations it attracts. Soils with a high CEC are excellent for growing crops, wildflowers, and garden shrubs. Clay and organic matter have negative charges, which means they attract cations. They hold nutrients and release them over time.
pH
All soils have a pH. They can be acidic, basic, or neutral. The pH level is important because it determines which plants you can grow. Some plants like acidic or basic soils, while others appreciate a neutral range.
Blueberries are a common example. They grow best in acidic soils with a pH between 4.5 and 5.5. If your garden’s soil is basic, or alkaline, you may add garden sulfur to lower the pH.
Most garden vegetables grow best in neutral soil with a pH of around 7.0. Some prefer slightly acidic conditions with a pH between 6.0 and 7.0.
Clay
Three main particles make up what we call soil: clay, sand, and silt. Clay is the smallest particle, which influences how it interacts with the others. It tends to stick together and form large clumps with tiny spaces.
Clay also has a high CEC, and it holds onto nutrients and moisture better than sand and silt. It’s a crucial part of a healthy, loamy soil.
Clay isn’t bad! It’s great when it’s in balance with other particles. It causes problems when there’s too much of it, as it’ll grow soggy when wet and dense when dry.
Silt
Silt is another soil particle that’s in between sand and clay. It’s medium-sized and an important part of a healthy soil.
Silt may also form large clumps when there’s too much of it. Instead of balancing the ground, it’ll cause issues for budding plants.
Sand
Sand is the final soil particle and the largest. It’s free-draining when there’s a lot of it, and it benefits plants that prefer dry, well-drained earth.
Sandy areas include beaches, deserts, and sand dunes. You’ll find palms, cacti, and other drought-tolerant plants that like growing in sandy soils.
Loam
Loam is the best type of soil for gardens, and a commonly misunderstood term. This technically describes a well-balanced, equal mix of clay, silt, and sand. In other words, it’s made of ⅓ clay, ⅓ silt, and ⅓ sand.
Loamy soils are ideal for a wide range of crops and ornamental plant species. If your dirt is too sandy or clay-rich, you may add organic matter to amend it into loam.
Organic Matter
Organic matter consists of anything rotting, decomposing, and breaking down. Wood, rotting food scraps, and garden clippings are all examples of organic matter. As it decomposes, it turns into humus.
Humus is not a tasty dip! It’s a soil particle that’s water-retentive and squishy. It’s an ideal part of a healthy garden. The more organic matter you add, the more humus your garden will have over time.
Rotting waste decomposes with the help of microbes, worms, and underground insects. The best way to harness them is with compost. Make a compost pile, or use trench and lasagna composting to rot waste in the growing site.
Macropores
You may know that some soils are free-draining and others are soggy and dense, but why are they like this? The answer is in the size of their pores. There are two types of pores, macropores and micropores.
Macropores are large spaces between soil particles. They’re common in sandy soils. The more macropores a site has, the more free-draining it is.
Loam has just the right amount of macropores and micropores. Too many macropores are harmful to moisture-loving plants and beneficial for those that thrive in dry conditions.
Micropores
Micropores are essential in healthy soils! They are tiny spaces inside clumps that hold onto water and nutrients instead of letting them drain. They hold onto these resources, and microbes and plant roots grow into the pores and access them.
Clay has more micropores than sand and silt. It tends to be nutrient-rich, as it holds onto water and fertilizer longer than the other particles.
Another way to look at pores is with “peds,” or clumps of sand, silt, and clay. The pores inside the peds are micropores, while the spaces between the peds are macropores. A healthy loam has a good balance of both.
Aggregation
Now that we mentioned pores, it’s time to discuss how they form! As worms burrow, roots grow, and microbes multiply, they change the dirt they’re in. They form spaces in between particles. These spaces create peds, the clumps of clay, silt, and sand.
Aggregation creates macropores as well as peds. In between the peds are the macropores. To encourage aggregation, add compost, leaf mold, or a similar organic mulch. Mulch protects plant roots and increases the number of worms and microbes in the dirt.
Compaction
Compaction is the opposite of aggregation. It encourages micropores rather than macropores, leading to water-retentive earth that holds onto moisture for long periods of time.
Compaction occurs because of gardeners, glaciers, and construction. Stepping on the ground compacts it, squeezing the macropores and creating more micropores. Home development and construction compact the ground to create a flat, level surface for building structures.
Glaciers leave hard, compacted dirt that’s impossible to work with. Consider using raised beds or containers if your yard is on a site where glaciers created a hardpan.
Soil Food Web
The soil food web is a chart of all the interacting organisms underground. It starts with the smallest microbes and works its way up to the top predators, like insects, birds, and rodents. Each organism impacts another, meaning they’re all inextricably intertwined.
Boost the soil food web by adding compost regularly. Compost is the best way to improve the garden. It mimics the mulch layer in forests, called duff. As leaves fall and animals die, they rot into a humus-rich layer that’s similar to compost.
Mycorrhizae
Mycorrhizae are fungi! They’re underground fungi that infect plant roots. Don’t worry, though, as this infection is a good thing. It’s a symbiotic relationship.
When mycorrhizae need sugars and carbon, they exchange water and nutrients for them with plant roots. This beneficial relationship allows forests, crops, and gardens to thrive despite harsh growing conditions.
More research is coming out about mycorrhizae and their incredible roles in the world’s ecosystems. It’s a fascinating topic to read up on!
