Fact Sheet FS1359
Introduction
Soil health is a term that refers to the overall condition of the soil to function in natural or managed ecosystems. The term "soil quality" is sometimes used interchangeably with "soil health," but soil quality is considered a broader term that includes inherent soil properties that are not easily modified, like mineralogy and particle-size distribution. Soil health, however, is focused on properties that can be modified by management in the relatively short term. In either case, it is important to consider the condition of the soil for productivity and long-term sustainability of Earth's ecosystems and populations.
Functions of Soil
Figure 1. The many functions of soil in Earth's ecosystems and human societies.
Credit: Food and Agriculture Organization of the United Nations.
The concept of soil quality or soil health is sometimes specific to a particular use or function. The functions of soil in the environment are numerous (Fig. 1); in addition to supporting plants, both physically and nutritionally, soils are important in the hydrologic cycle, serve as habitat for diverse organisms and their unique genetic biochemicals, and are the site of storage and recycling of nutrients and carbon. In addition to ecosystem services, soils provide food, fiber, and fuel to support the human population, as well as construction materials and the engineering foundation for society's infrastructure. The characteristics of soil that are most important for growing crops are, to some extent, different that those required for infiltrating, purifying, storing, and transmitting rainwater to groundwater.
Soil Health Indicators
Just as with human health, soil health requires many factors and processes to be working individually and in concert with each other. Measurements or characterization of the major factors allow us to develop an assessment of soil health for specific areas of land. The factors that have been shown to be most influential in determining soil health for many functions include:
Chemical Factors
Physical Factors
Biological Factors
Notice that 'organic matter' can be considered under each of these categories of soil health indicators. There are other factors that can be considered and may be significant for specific functions, but this listing demonstrates that a "good" content of organic matter is extremely important for most assessments of soil health. While most healthy soils will still fall into the ranges of 90–97% inorganic (that is, mineral) and 3–10% organic matter by weight, the relatively small proportion of organic matter in soil is essential for good chemical, physical, and biological conditions. Organic matter can be added directly to soil, as compost for example, or can be increased indirectly by a combination of management practices that increase vegetative productivity and foster robust soil biology.
Managing Soil for Healthy Ecosystems
Figure 2. The specific practices may differ by situation, but the general principles of soil health are the same.
Credit: USDA-Natural Resources Conservation Service.
Best management practices (BMPs) for improving or maintaining soil health have been described by various organizations and agencies, but they are similar in general concepts (Fig. 2).
Minimize Disturbance
Tillage, excavation, grading, and other manipulations of soil can damage or destroy its structure that developed over hundreds or thousands of years, as well as disrupting the biological communities. Disturbance, such as tillage, often will also allow high rates of organic matter decomposition. Compaction of soil, which destroys large pore spaces and creates dense layers of soil, prevents adequate drainage and aeration and inhibits root growth. However, in cases of existing compacted soils, tillage may be necessary to initiate recovery of soil health.
Maximize Living Roots
Plants are Earth's major primary producers, fixing carbon to supply energy to the rest of the food web. The plants and other organisms in the food web supply organic matter to the soil. The roots also contribute to soil porosity as they grow and die. The dense, fine roots of a grass sod are particularly beneficial in promoting soil aggregation and minimizing erosion, while tap-rooted plants have been shown to be useful in alleviating soil compaction. Maintaining adequate nutrients and suitable pH are important practices to assure plant establishment, growth and inputs to roots.
Maximize Soil Cover
"Topsoil" is usually the most valuable layer in terms of nutrients, organic matter, structure, and organisms but most vulnerable to erosion. Maintaining cover on the soil – whether live vegetation, plant residues, or mulch - greatly minimizes the risk of erosion. Furthermore, cover will decrease evaporation to maintain adequate water for plants and moderate soil temperature to acceptable levels.
Maximize Biodiversity
A diverse ecosystem is highly resilient to changes in the environment. It creates a balance of types of plants and other organisms which have differing responses to change but overall allows the ecosystem to continue functioning (Fig. 3). For example, it prevents large buildup of a disease organism that can decimate a crop monoculture.
Figure 3. A healthy soil supports a wide range of organisms that help to maintain ecological balance.
Credit: USDA-Natural Resources Conservation Service.
These guidelines will foster benefits to soil that result from vigorous biological activities, organic matter accumulation, and development of structure and porosity. In addition to these general guidelines, it is assumed that to preserve its value (that is, ability to function in the ecosystem), a healthy soil will be protected from all possible forms of degradation.
Preventing chemical degradation would include avoiding contaminants such as heavy metals, xenobiotics, pharmaceuticals, and excess salts. Use of pesticides should be limited as much as feasible to avoid unintended impacts on the ecosystem. Routine soil testing provides recommendations to maintain good growing conditions for the vegetation and soil organisms.
Physical degradation also can take many forms. Soil compaction (densification) often occurs due to excess loads, traffic, and smearing (shear forces), especially when wet. Erosion of the rich topsoil by water or wind not only depletes the land but also has downstream or downwind consequences. Pollution by fragments of plastic (micro- or nano-plastic), broken into tiny pieces but not decomposed by soil microbes, has both chemical and biological consequences.
Actions that drastically eliminate organism populations or upset the ecological balance of soil should be considered biological degradation. These would include use of excessive tillage, overgrazing, incursion by invasive exotic species, and unconstrained use of pesticides, for example.
Recommendations for specific practices may vary depending on the particular land use or crop situation, but application of these general principles have been shown to advance the health of soil over time (5–20+ years, depending on initial condition and practices adopted). In the shorter term, applying amendments as prescribed by soil tests, promoting lush vegetative cover, and building soil organic matter in depleted soil will allow you to begin the process of building soil health.
References
Resources
August 2024
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