Hobby Farms Editors
May 26, 2014
Why is Soil Great for Plants? The Answer Isn't As Obvious As You’d Think - Photo courtsy USDA/Flickr (HobbyFarms.com)
Photo courtesy USDA/Flickr

Unless you’ve constructed a hydroponic system on your farm, it’s impossible to grow plants without soil. Soil is the backbone of our farms, and something we need to pay careful attention to if we want plentiful, nutritious, disease-free crops. If you’re not already convinced of the benefits well-tended soil brings to your plants and farm, here are nine things you’ll want to keep in mind.

1. Soil Offers Support
Without the roots anchoring plants to the soil, plants would flop over on the ground instead of growing upright.

2. Soil Absorbs Water
The main function of plant roots is to absorb water (and nutrients) from the soil to meet the needs of the plant for transpiration. A large tree can transpire 40,000 gallons (150,000 l) of water in a year—enough to drain a small backyard swimming pool. Without the store of moisture in the soil, it would need to rain about 2/10 inch (5 mm) each day just to keep up with the immediate needs of the plants. Alternatively, you would have to supply that amount of water with a hose.

3. Soil Stores Nutrients
Every soil has a significant store of nutrients that plants can use. We may have to add some extra to make up for a shortfall, but this is just a small part of the total nutrient uptake by the plant. To understand this better, consider the nutrient mixtures that are needed for hydroponic production, where the growing medium (e.g., rock wool or coconut fiber) doesn’t provide any nutrition. The hydroponic solution must include all the essential elements, in the proper proportion, as well as some other beneficial elements (like silicon and sodium), or the plants will not survive. In most gardens, we need to supply only a few nutrients; the rest are already there.

4. Soil—When Properly Tended—Allows Air
We don’t usually think of roots as having to breathe, but the cells in the roots need oxygen if they are going to perform their functions. If the soil is completely flooded, most plants will die because oxygen cannot get to the roots. Plants that are adapted to wet conditions, such as rice, have special tubes inside the stem that carry air down to the roots so that the roots don’t need to get air from the outside. This group, however, does not include many of the common garden plants.

5. Soil Provides Temperature Moderation
Soil does not warm up as quickly as does the air when it’s hot, nor does it cool down as quickly when the air is cold. While this can cause us to feel impatient in the spring, when the sun shines warmly and we want to get seeds in the ground (it’s almost always best to wait), the “heat sink” in the soil can provide real benefits during the growing season.

On cold spring nights, the warmth stored in the soil during the day can moderate the temperatures around young seedlings and prevent cold shock or frost damage. Later in the summer, the soil keeps the temperature in the crop canopy from rising too high during extreme heat, protecting the plants from stress. Again in the fall, as the weather starts to cool down, warmth released from the soil can provide protection from early frosts.

6. Soil Acts as a Reservoir
When it rains or when snow melts in the spring, much of the water soaks into the soil. Depending on the soil texture, this water drains through the soil either quite quickly or very slowly. Some of the water is held near the soil surface, where plants can reach it, while a portion moves deeper into the soil. The water that drains down to the water table can percolate into groundwater to replenish our aquifers or flow laterally to feed streams and rivers during the dry summer months.

7. Soil Acts as a Filter
Water is very effectively filtered when it percolates through the soil. Sediment and bacteria particles are caught in the small spaces between soil particles and left behind. Electrostatic charges attract and hold more potential contaminants, and the active biology in the topsoil breaks down many organic materials that could otherwise impair water quality. This is why most well water can be drunk safely just as it comes from the ground, without any further treatment.

8. Soil Acts as a Climate Modifier
Soil affects the climate both at the level of individual plants, as described above, and on a global scale. On the larger scale, soil is an effective carbon sink, absorbing carbon rather than releasing it into the atmosphere as carbon dioxide, a greenhouse gas. Increased levels of carbon dioxide in the atmosphere have been linked to changes in average temperatures and weather patterns. Good soil management can trap a lot of carbon by increasing soil organic matter.

9. Soil Creates Habitat
The soil is a diverse ecosystem on its own, but it is also home for a number of creatures that we see only during the aboveground phase of their life cycle. The cicadas that buzz from the trees on hot summer days spend most of their lives underground, emerging only to mate and lay eggs. Most crickets, grasshoppers and locusts spend part of their lives in the soil, although for many, the soil serves primarily as protection for the eggs; the nymphs emerge from the soil soon after they hatch. Mammals also use the soil as a home. Woodchucks, badgers and prairie dogs dig extensive underground burrows, coming out only to feed. These burrows, in turn, may eventually become dens for foxes or rabbits. The insulating value of the soil keeps these creatures cool in the summer and warm in the winter.

Boost your soil with these gardening tips:

About the Author: Keith Reid is a soil scientist with over 30 years’ experience assessing and advising growers about soil issues.

Used with permission from Improving Your Soil: A Practical Guide to Soil Management for the Serious Home Gardener
by Keith Reid, Firefly Books 2014, $29.95 paperback. Read the HobbyFarms.com review here!


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