Earthworms are relatively complex in terms of their internal structure, but their contribution to soil health is straightforward. While people may recognize that earthworms are beneficial for the soil, they may not fully understand these organisms in order to use them to their full potential. Below, we will briefly explore the role of earthworms and how agriculture can influence them.
 

What are earthworms and what do they do?

There are three general species of earthworms: epigeic worms, that are surface dwellers, endogeic worms, that live just below ground, and anecic worms, that live below the soil but frequent the surface to obtain food. Earthworms are often called “ecosystem engineers,” as they provide numerous benefits to the soil. Through burrowing, they aerate the soil, enhancing soil structure, water infiltration, air circulation, and nutrient cycling. Additionally, they consume organic matter on the soil surface, kickstarting the decomposition process. Through mixing the soil, consuming organic matter, and leaving behind their casings and wastes, earthworms make nutrients more readily available to plants. Benefits provided by earthworms may not be seen as easily aboveground, as they are belowground. The increase to soil stability, drainage, and nutrient cycling are all characteristics to soil that can be beneficial to crop success. Earthworm tunnels can also provide pathways for roots, and in heavier soils that can be a plus. All these activities allow for plants to not have to search for nutrients or water but have them more readily available throughout the topsoil.
 

What are the best conditions for earthworm survival? 

Although earthworms can be abundant in the soil, environmental conditions can influence their presence. Soil characteristics such as pH, moisture, soil texture, temperature, compaction, and surface residue all influence earthworm populations. For example, soils that are silty, moist, warm, have organic matter, and a pH from 5.0-8.0 provide an ideal environment. While earthworms can adapt to a variety of soil conditions, they are considered indicators of soil health as their presence reflects the quality of the soil. Typically, in a 1 ft2 area that is 6-8” deep, 8-10 earthworms should be found to indicate a healthy population.

How does agriculture influence earthworms? 

Starting with soil disturbance, conventional tillage can damage earthworms themselves and their tunnel systems. Different earthworm species respond differently to tillage, but deep and continuous tillage methods are more likely to decline earthworm populations. Studies have shown that no-till or reduced-till systems, along with annual forages, support larger earthworm populations with reduced soil disturbances. By not incorporating the residue into the soil, you provide earthworms with a protective cover and an adequate food source. Tillage buries organic matter and leaves worms vulnerable to predators on the soil surface. Another key factor influenced by agriculture is organic matter. Earthworms rely on organic matter as their primary food source, so ensuring there is an adequate quality and quantity of organic material is essential to sustain earthworm populations. However, incorporating organic matter to your fields can be challenging, depending on the crops and farming practices currently in place. It is important to note that it takes years of management practices to increase earthworm populations, therefore this is not a quick fix but rather a long-term investment.

How can you maximize the benefits of earthworms? 

There are various studies and perspectives regarding the impact of agriculture on earthworms. While soil disturbance does harm earthworm populations by damaging their tunnels and reducing their food source, this does not necessarily mean a complete switch to no-till is required. Considering a reduction in the depth, timing, and frequency of tillage can be enough to improve earthworm populations without changing your operation entirely. Regardless of tillage methods, the key to maintaining healthy earthworm populations is ensuring a consistent supply of organic matter for them to feed on. This can include leaving your corn stalks or wheat straw instead of bailing, or planting cover crops. Another option is applying livestock manure. Finally, if your soil pH is too low, slowly bringing that up to tolerable conditions can promote the inhibition of earthworms. These practices help maintain a healthy environment for earthworms, and in turn, benefit soil health and plant productivity. The Soil Conservation Council of Canada came up with an initiative in 2017, to encourage people to get out and look at their soil health. By placing cotton fabric in the soil for two months, you are able to determine the health of your soil. Fabric that is still relatively intact, indicates that the soil health is poor, compared to fabric that is highly decomposed, your soil would be considered healthier. You can read more about the initiative here if you are interested: https://soilcc.ca/soilchampions/soil-your-undies/.