Soil… It’s Alive!
IN THE GARDEN for February 2013, Kendall Weyers, Nebraska Statewide Arboretum
Possibly the most important factor in growing healthy landscape and food garden plants may be the least appreciated or understood—soil. It’s not easy to see, but good soil is a highly functioning and incredibly dynamic ecosystem. According to the USDA Natural Resources Conservation Service, “soil is by far the most biologically diverse part of the Earth.”
The complex soil food web is versatile and adaptable, and includes microorganisms (bacteria, protozoa and fungi), earthworms, spiders, beetles, springtails, pillbugs, ants and other arthropods. That list might make your skin crawl, but all these creatures work together to contribute to more productive soil. They:
- Process organic matter. Each organism on the list helps break down organic matter on top of and in the soil, improving the physical and chemical properties of the soil. The main benefit of this process is the nutrient cycling that occurs, recycling the organic residues into nutrients to make them available and accessible to plant roots.
- Create beneficial symbiotic relationships. There are specialized bacteria and fungi that form mutually beneficial relationships with plants. Rhizobia are bacteria that allow legumes to collect nitrogen from the air. Mycorrhizae are host-specific fungi that attach to roots and create extensive systems of filaments that act like an extension of the root system. This greatly increases the plant’s ability to take up water and nutrients and increases the plant’s tolerance of environmental stress.
- Filter and store water and air. As the creatures move through the soil, they create channels and space for water and air to move down into the soil. This increases the availability and capacity for these soil components, both of which are critical to plant health and survival.
- Control pests. A biodiverse soil does a tremendous job of keeping a wide range of pest organisms in check. Keep this in mind before using pesticides—they reduce the number of beneficial organisms, not just the intended target pest.
- Stabilize soil. One result of microorganisms breaking down organic matter is a highly stable material called humus. Humus binds soil particles together into aggregates or clumps. This improves soil structure and makes the soil more resistant to erosion. Humus also buffers the soil pH, helping to keep it in a range ideal for plant growth.
- Store carbon. Humus, the end product of organic matter breakdown, can contribute greatly to carbon storage. It is highly stable and can sequester carbon for decades.
There are a number of things you can do to increase the biodiversity of your soil and reap the many benefits diversity provides. The good news is that these organisms are probably already present. Even if their numbers are low, populations will increase rapidly with favorable conditions you can provide by:
- Adding organic matter. Organic matter is the key food in the soil food web. It can be increased by incorporating compost and plant residues into the soil.
- Mulching with organic materials. Mulch helps moderate soil moisture and temperature, and adds organic matter as it breaks down. Plus it helps prevent compaction from foot traffic and heavy rain.
- Watering properly. Soil organisms thrive in damp but not soggy conditions. Over-irrigating can create adverse conditions harmful to many beneficial organisms.
- Limiting use of pesticides. As mentioned earlier, applications of pesticides (insecticides, fungicides, herbicides) often kill beneficial organisms in addition to the target pest.
- Limiting tillage. Excessive tilling can be devastating to beneficial fungal networks and soil structure.
- Avoiding compaction. Compaction, whether from pets, people or vehicles, reduces the ability of soil to provide essentials of air and water.
Soil is a hidden miracle of nature, a complex web of self-sustaining interaction right under your feet. Considering the many benefits of a biodiverse soil, it is worth the time to nurture and appreciate.