Understanding the Soil Profile and How it Affects Plant Growth
There is more life below the soil surface than there is above and much of that life is so tiny it is difficult or actually impossible to see without the aid of a microscope. These tiny life forms include mites, springtails, nematodes, viruses, algae, bacteria, yeast, actinomycetes, fungi, and protozoa. An astounding 50 billion microbes can live in 1 tablespoon of healthy nutrient-rich soil. All of this life works together to keep the soil profile healthy and balanced and ready to support plant life- such as the flowers and vegetables you plant in your garden.
“Soil-dwellers move through the soil, creating channels that improve aeration and drainage. Nematodes and protozoa swim in the film of water around soil particles and feed on bacteria. Mites eat fungi, and fungi decompose soil organic matter. The microorganisms’ primary role is to break down organic matter to obtain energy. Microorganisms help release essential nutrients and carbon dioxide and perform key roles in nitrogen fixation, the nitrogen and phosphorus cycles, denitrification, immobilization, and mineralization. Microbes must have a constant supply of organic matter, or their numbers will decline. Conditions that favor soil life also promotes plant growth. Unfavorable soil conditions, such as high temperatures, compaction, or oversaturation can injure beneficial soil life. This can lead to a proliferation of disease-causing fungi, bacteria, or viruses” (NC State Extension).
What is the Soil Profile Exactly?
The soil is a living, breathing, natural entity composed of solids, liquids, and gases. The soil profile has five major functions or roles that it performs as part of the natural balance of things. Soil:
- Provides habitat for organisms
- Recycles waste products from living organisms
- Filters water as it leaches through the soil particles
- Serves as an engineering material to build other structures
- Provides a medium for plant growth
The final role of soil is the one most people think of first and it is the one that has the greatest and most direct impact on human life. Soil that is perfect to support plant growth contains 50% porespace and 50% solid material. The open areas in the soil known as porespace are what gets filled with equal parts air and water and allow things like plant roots and burrowing creatures to move through the soil. This is the ideal distribution and it rarely occurs because porespace varies with soil texture and how well the soil has been cared for. Ideally, for plant growth, most soil scientists agree that 50% porespace, 45% mineral matter, and 5% organic matter make up an ideal ratio
Understanding The Soil Profile
The vast majority of homeowners today confuse plant nutrition with fertilization. Plant nutrition is what scientists call the basic elemental needs of the plant and how a plant uses the basic chemical elements to grow- much like how we humans use certain nutrients and minerals to grow new calls and keep body functions running smoothly. Fertilization is the term used when these elements are supplied to the soil throughout outside intervention by humans. Nutrients added to the soil will affect the soil profile with supplemental materials. This is what is known as fertilization of the soil. Adding fertilizer during unfavorable growing conditions will not enhance plant growth and may actually harm or kill plants and it is entirely possible to put too much fertilizer in the soil. All the vitamin C in the world will not help a person who is dying of cancer and too much vitamin C can actually poison a person. The same is true with the nutrients that fertilizers put into the soil. If a plant is sick, giving the wrong nutrients can do more harm than good!
“To complete their life cycle, plants need 17 essential nutrients, each in varying amounts. Of these nutrients, three are found in air and water: carbon (C), hydrogen (H), and oxygen (O). Combined, C, H, and O account for about 94% of a plant’s weight. The other 6% of a plant’s weight includes the remaining 14 nutrients, all of which must come from the soil. Of these, nitrogen (N), phosphorus (P), and potassium (K), the primary macronutrients, are the most needed. Magnesium (Mg), calcium (Ca), and sulfur (S), the secondary macronutrients, are next in the amount needed. The eight other elements—boron, chlorine, copper, iron, manganese, molybdenum, nickel, and zinc—are called micronutrients because they are needed in much smaller amounts than the macronutrients” (NC State Extension).
Changes in the Soil Profile
Soils change in three dimensions- from the top to the bottom, from north to south, and from east to west. The practical meaning of this three-dimensional variability is that as you move across a state, a county, or even a field, the soils change. Five factors of soil profile formation account for this variation:
- Parent material that the soil originated from in the beginning
- Biological activity from environmental factors in the area
- Climate effects from weather and temperature and moisture
- Topography that affects compaction, runoff, and erosion
- Time and how long the soil particles have been exposed to the elements
Differences in even one of these factors will result in a different soil type. Soils can change when they originate from different rocks and materials, when moisture and temperature affect organic matter levels, and when erosion and other factors carry nutrients and elements from one area of the soil to others.
How Do Soil Types Affect Gardeners?
There are three key ways soil types can affect gardens and the types of plants that can easily be grown. These three ways are the levels of nutrients found in the soil profile, how much compaction has occurred, and how badly the soil has been eroded.
Just as humans need food and nutrients to grow and stay healthy, so do plants. Not all soils have the same amount of nutrients and thus not all soils can support the same type of plants. Sandy soils are often very low on nutrients and do not hold water for very long making it hard to grow many types of plants without adding material to the soil to make it better. Soils with a lot of clay will have more nutrients than sandy soils but they often drain slowly which means plants can get too much water if sand is not added to the soil to improve drainage. Soil that has a lot of fine particles can often lose nutrients as the rainwater leeches through the soil and the opposite can be true of soil that is too heavy and coarse and does not have enough air space in it.
Compaction occurs when pressure is applied to soil particles and the air and water are pushed out of the pore spaces. Large, cubic sand particles are not easily compacted. Clay particles can compact much easier than sand, especially when wet. Compaction of the soil profile inhibits the movement of water, air, and roots. Compacted soils have less infiltration, greater runoff, a higher risk of erosion, and more restricted root growth than soils without compaction. It is harder for plant roots to grow through compact hard soil so the plants will not grow as well and will not be as healthy. Water drains slowly, which may increase the likelihood of plant root diseases and poorer growth within the soil profile and fewer available nutrients to keep plants healthy if they do manage to take root in compacted soils.
Erosion is the process where the particles of soil are moved from their original place to another location which causes there to be less soil for plants to grow and poorer soil where the soil still remains after the effects of erosion have taken place. Not all soil types erode the same way. “Sand particles are heavy, so they are not easily picked up and moved by water or wind. Clay particles are sticky, so they are not easily moved. Silty loam particles are light and not sticky, so erosive forces easily move them. Eroded soils are usually harder to till and have lower productivity than soils without erosion” (NC State Extension). This is what happened long ago with the Dust Bowl out West when the soils were eroded due to poor management and the remaining soil was not suited for plant growth and farming.
Soil erosion can be minimized by following a few preventive measures:
- Choose plants that can easily grow in the naturally occurring soil profile
- Mulch the surface of the soil whenever possible to reduce wind and rain erosion
- Adequately fertilize to promote vigorous, but not excessive, plant growth
- Create channels and berms to control the flow of water and to reduce water erosion
- Align rows to follow the land’s contour so that water flowing downhill is slowed.
- Use proper tillage methods and protect root systems of perennial plants like grasses
- Plant a winter cover crop to avoid leaving the soil exposed for long periods of time
- Consider installing rain gardens and other features to hold rainwater and slow runoffs
Contaminated Soil and Garden Crops
As the locally grown food movement gains momentum, more people are gardening in urban areas. Urban soils can be host to contaminants such as lead, pesticide residue, or petroleum products. The elements that are in the soil can get into the plants that grow in that soil. This may have an impact on the health of flowers but for plants that we eat this can cause the fruit to become contaminated as well. Also, working in contaminated soil can put you at risk when you put your hands into the dirt and get the soil on your clothes.
Here are some tips for gardening in contaminated soil profiles according to NC State Extensions:
- Plant ornamentals in known contaminated areas if you must plant there
- Keep edibles like vegetables as far from the bad soil as you can
- Do not plant near roads or buildings where pollutants can wash into the soil
- Consider using raised beds with imported soil to keep plants away from contaminated soil
- Raising the pH of the soil may help to slow the rate some plants absorb contaminants
- Organic matter, such as compost, can lock some types of contaminants in the soil
- Professionals can assist with farmland or large scale contamination control
- Soil profiles need constant care and attention if you start changing things so work in small areas
- Avoid crops where edible portions of the plant are in direct contact with contaminated soil
- Shoot and leaf crops will have less of a contamination risk but can still be affected
- Fruit crops and tree crops will have the least amount of contamination risk
- Rremember you can amend the soil profile to lessen the amoutn fo containated soil in an area
- Wear gloves at all times when working the soil and wash hands and clothes after gardening
- Do not wear garden clothes into the house and be sure to take and leave shoes off outside
- Watch children closely when in the garden to ensure they don’t eat the dirt as they play
- Wash produce and peel or remove outer leaves before eating anything grown in the soil
Contact Us For Help Getting Your Soil Ready to Garden
Most people enjoy looking at the beautifully landscaped yards in their neighborhood and enjoy relaxing on the porch or patio or in a hammock in their own yards even more. There is nothing quite like being surrounded by the beautiful plants of your own yard. Beautiful yards that everyone can enjoy do take work but they do not have to turn you into a slave. You can have the yard of your dreams without sending every weekend slaving away with water hoses, fertilizer, and a stack of cash. The key is to start with the right type of soil and if you do not have the best soil, then you need to know what to do to fix the soil so it can support your garden dreams. We here at Country Landscape and Supply can help you with all of your soil and garden need so be sure to call us today to schedule a consultation appointment with our team! Your dream garden is closer than you think and we can help you get started off on the right foot with the right soil for your gardening plans!