Soil health is defined by Natural Resources Conservation Service (NRCS) as the capacity of soil to function as a living ecosystem that sustains plants, animals, and humans. Healthy soils contain billions of bacteria, fungi, and other microbes that help form an ecosystem, providing nutrients for plant growth, absorbing and holding water, and providing the foundation for agricultural activities.
|Soil organisms living within a soil aggregate. Credit: S. Rose and E.T. Elliott, USDA-NRCS.|
Follow four basic soil health principles to improve your soil health and sustainability:
- Keep the soil covered. Examples of cover are leaving plant residue behind after harvest, or mulching your garden.
Erosion by wind and water happens when the soil is not adequately covered. Keeping your soil covered as much as possible protects your nutrient-rich top soil.
In addition to soil erosion, cover can affect soil temperature and moisture. A soil covered with plant litter/mulch reflects radiation due to its “albedo.” This keeps soil temperatures lower than bare soils, which warm up more readily. Especially during the summer, the temperature difference between a covered and bare soil can be significant. Plants use soil moisture less efficiently at higher temperatures as more water is lost through evapotranspiration than utilized for plant growth.
- Minimize soil disturbance. Examples of soil disturbance are tillage, overgrazing, and overapplication of chemicals and nutrients.
Soil disturbance such as plowing and rototilling can impact soil by physically breaking up the soil structure and by stimulating microbial decomposition of organic matter. This includes the breakdown of biological glues, such as polysaccharides and glomalin, that are key in maintaining soil structure. Without these biological glues, when the soil gets wet, it collapses and loses large soil pore spaces resulting in a net reduction in infiltration, aeration, and soil microbial activity. Disturbed and compacted soils sometimes more closely resemble a brick than a healthy functioning soil!
- Use plant diversity. Examples of diversity are using crop rotations or planting a variety of species for pastures or cover.
By increasing the diversity of plants above ground (at the same time or in a crop rotation), the diversity below ground can be enhanced. Diversity can build redundancies and synergies in the soil system which ultimately leads to increased resiliency (to drought for instance). Many would argue that this is the most important principle to improve soil health/function and increase long-term sustainability. For an added incentive, increasing crop diversity in agricultural systems has long been recognized as a tactic for increasing economic resiliency.
- Keep living plants throughout the year - most commonly achieved by using cover crops.
Soils feed plants and plants feed soils. Through photosynthesis plants capture soil energy and convert it to organic compounds (from simple sugars to complex organic molecules like lignin). Plants use this captured solar energy for maintenance and growth. Most soil organisms need this external food source produced by plants.
Many plants “leak” carbohydrates and other root exudates to stimulate soil microbial activity. Fueled by this symbiotic relationship, the area around the root (rhizosphere) is teaming with life in a healthy, functioning soil. This biological activity drives nutrient cycling in the rhizosphere. Many plants also form symbiotic relationships with mycorrhizal fungi by providing carbon to the fungi in exchange for nutrients (especially phosphorous). In these instances, soil microbes are providing services to the plant (i.e. nutrient cycling) at the cost of organic compounds from the plant.