Sow and Grow with Sara: Soil health and earthworms

Earthworm populations varied due to soil conditions from just over 285,000 up to 2,000,000 worms per acre. The study found that on average, cover crops had more than twice as many earthworms as the control plots with no cover crops.

According to a 2001 paper (Land degradation: an overview), it is estimated that the total annual cost of erosion from agriculture in the USA is about $44 billion per year, i.e. about $100 per acre of cropland and pasture. On a global scale, the annual loss of 75 billion tons of soil costs the world about $400 billion per year, or approximately $70 per person per year (Eswaran, H., et. al. 2001).

Every producer has their own unique way of operating that is most effective and familiar to them. However, nearly everyone has room for improvement within their business model. One of the changes I challenge growers to strive for is better soil health management and planning.

In South Dakota we have adopted 5 “Principles of Soil Health”. These include:

1. Soil Cover- keeping plant residue on the soil surface at all times.

2. Limited Disturbance- minimize or completely avoid tillage in order to allow soils to build

aggregates, pore spaces, organic matter, and improve biological activity.

3. Plant Diversity- mimic nature by using cool and warm season grasses and broadleaf plants. For example, this includes adding a mixture of cover crops and/or small grains to a strictly row crop rotation.

4. Living Roots- allowing cover crops to grow in the off-season provides carbon to the soil and serves as a food source for microorganisms.

5. Integration of Livestock- allowing livestock to graze cash crop and cover crop residue provides more forage options for producers at a time of year when forage quality and supply begins to drop. In turn, livestock grazing increases soil biological activity, improves nutrient cycling, and helps improve overall soil health if grazing is properly managed.

The principles work synonymously with one another, and the more regenerative-type practices that are added to a cropping system, the more benefits your soils will experience.

Essentially, the more we can mimic nature, the better our cropping systems should function.

There are many different ways to measure soil health such as water infiltration, soil compaction, soil biological testing, organic matter, etc. One unique way is to look for earthworms. Healthy soils are full of natural organisms that range from rabbits and insects, to microscopic beings.

Earthworms fit into a very special category. They have the capability to do ‘tillage’ in no-till soils. As they move through the soil searching for food and water, tunnels are created. These tunnels improve soil porosity and ultimately soil health. Their existence above and below ground speeds up the breakdown of organic materials in the soil and improves the carbon and nutrient status, making them more available to crops.

Each time a tillage pass runs through a field, soil structure is broken down, but what often isn’t noticed is that earthworm populations are significantly affected. A recent study conducted by SDSU Extension personnel looked into earthworm populations. They selected sites that were no-till for 15 years or longer and where cover crops were planted in the fall of 2019 after small grain harvest. A control plot was established by spraying out 15x30’ plots at each site. In the spring of 2020, project coordinators returned to count earthworm populations using an established protocol that involved pouring mustard-vinegar solution into rings to bring worms to the soil surface (Chan and Munro, 2000).

Earthworm populations varied due to soil conditions from just over 285,000 up to 2,000,000 worms per acre. The study found that on average, cover crops had more than twice as many earthworms as the control plots with no cover crops.

As one might expect, soils won’t vastly improve overnight, but by slowly adding the principles of soil health to your operation, a more resilient and healthy cropping system (with increased earthworm activity among other positive soil health indicators) should emerge.

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