If you are used to thinking of soil as a physical medium for growing plants, then the idea of a healthy soil doesn’t make much sense. It is true that soil is composed of physical components- sand, silt, and clay, for example- and chemical components. Soil also has a biological component. Did you know that a teaspoon of soil can contain up to a billion microbes? Those microbes, along with earthworms and other arthropods, are just as vital as the physical components are for growing plants. In this way, you can think of soil as an entire ecosystem, and the health of that ecosystem- just like human health- can be measured by how well that soil functions.
Unhealthy soil doesn’t function very well to support life, at least not for the long term. Unhealthy soil is more vulnerable to drought, excessive rain and erosion. When rain falls on unhealthy soil, the water either runs off the field (taking the soil with it), or it ponds on the surface and drowns out plants. Unhealthy soil is also often compacted, which limits the growth of plant roots and results in shallow or stunted root systems.
Healthy soil, on the other hand, is more resilient to extreme weather and other stresses. When rain falls on healthy soil, it soaks into the ground like a sponge and is available for crops to use. Healthy soils have fewer issues with compaction- some farmers have remarked that one of the first things that they notice when their soil health improves is that the ground feels more resilient and can support farm equipment without creating ruts or getting stuck. Healthy soil also has benefits off the farm, including improved water quality and carbon sequestration to help reverse climate change.
Principles of Soil Health
There are four principles for farming practices that help to improve soil health. They are:
Limit disturbance. Soil is “home” for microbes, fungi, insects and earthworms, and like a house, soil has structure that creates habitat and supports the right balance of air and water. Disturbing the soil breaks that structure down and hampers the function of the soil ecosystem. Disturbance can include tillage as well as some chemical inputs.
Keep the soil covered. Both living plants and plant residue act like armor, protecting the soil from erosion by wind or rain. In a heavy rain, those living plants and residues reduce the energy of falling raindrops and running water so that the soil stays in place and doesn’t form a crust on the surface. Residues also act like an insulation blanket, helping to moderate high temperatures in the summer and freezing temperatures in the spring and fall.
Keep a living root throughout the year. One of the main sources of food for soil microbes is produced by plant roots. It’s an amazing and complex process in which plants produce root exudates that feed the microbes, and in turn, the microbes convert nutrients in the soil to compounds that can feed the plants. When land is left fallow after crops are harvested, that engine stops running. By keeping living roots in the soil all year round, those soil microbes are ready to go when crops are planted.
Add diversity. Think of a forest, or wetland, or prairie ecosystem and how many different kinds of plants and animals are found there. Those natural systems contain diversity for a reason. For one thing, different species fit into different niches in the system- one plant can grow in a shady part of the forest, while another plant requires more sun, for example. Having multiple species that fit into similar niches helps to make the system more resilient as well, because if something happens to one kind of plant, the similar plants can perform the same function. Diversity in cropping systems helps to support the other principles of keeping soil covered and living roots throughout the year, and also helps to break up pest cycles and reduce the need for pesticides.
Some experts also include a fifth management principle: Incorporating livestock. Livestock help to improve soil health by turning plants into fertilizer. Manure is high in organic matter, nutrients, and beneficial microbes. In addition, the hooves of grazing livestock also help to break up plant residue and work it into the soil. Livestock need to be managed carefully to avoid overgrazing and compaction, but they can also provide a “jump start” to the soil health in a field.