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Beneficial Earthworms Are Being Destroyed by Annual Plowing


Story at-a-glance -

  • Earthworms are essential to soil health and help increase organic matter, provide aeration and improve soil’s ability to absorb water
  • In intensively farmed fields, fewer than 30 earthworms live in each square meter of soil compared to up to 450 worms in soil that’s rarely plowed
  • Disturbing the soil less using no-till or conservation agriculture led to significant increases in earthworms, by 137 percent and 127 percent respectively

By Dr. Becker

An ecosystem is only as healthy as the health of its soil, and soil health is facing increasing threats from intensive industrial agriculture. One of soil's primary inhabitants, earthworms, are also becoming unwitting victims to modern-day farming, and their numbers may be dwindling as a result.

For a creature that's often viewed as creepy and slimy, earthworms are quite magnificent and provide a great service to humankind. In some areas, earthworms contribute between 40 percent and 90 percent of soil macrofaunal (invertebrates that live in sediment) biomass and 8 percent of total soil biomass.1

As worms burrow through the soil they eat decomposing plant matter, including leaves and roots. In return, they leave behind nutrient-rich excrement, full of nitrogen, phosphorous and calcium that plants need to grow.2

Meanwhile, the tunnels they make through the soil provide aeration and improve its ability to absorb water, which not only helps plants to grow but also reduces flooding. Little concrete data exists on earthworm numbers worldwide, but it's known that these creatures have a harder time surviving in areas of intensive agriculture — the same areas that could use their services the most.

Annual Plowing Is Reducing Earthworm Populations

In an "Earthworm Manifesto" published to bring attention to the earthworm's plight, the World Wide Fund for Nature (WWF) reported that in intensively farmed fields, fewer than 30 earthworms live in each square meter of soil. For comparison, in fields that are rarely plowed, up to 450 worms may live in the same amount of space.3

Research published in Global Change Biology, which used data from 215 field studies in 40 countries, also revealed declines in earthworm populations in soils that are plowed annually.4 Associate Professor Olaf Schmidt, Ph.D., from the UCD School of Agriculture and Food Science, University College Dublin, said in a press release:5

"What we see is a systematic decline in the earthworm population in the soil after continued ploughing and a significant increase in the abundance of earthworms in less disturbed soil, although some soils would need more than 10 years to show good signs of recovery."

Disturbing the soil less using no-till or conservation agriculture led to significant increases in earthworms, by 137 percent and 127 percent respectively. Soil biomass also increased by 196 percent and 101 percent, respectively, using no-till or conservation practices compared to typical plowing.

Notably, epigeic (which live in the surface layer and do not form burrows) and the larger-sized anecic earthworms (which can burrow into deeper layers of the soil) were found to be most sensitive to conventional tillage and experienced the greatest positive responses when tilling was reduced. The researchers noted:6

"The restoration of these two important ecological groups of earthworms and their burrowing, feeding and casting activities under various forms of reduced tillage will ensure the provision of ecosystem functions such as soil structure maintenance and nutrient cycling by 'nature's plough.'"

Earthworms: The Least Appreciated Creatures on Earth

WWF farming sector expert Birgit Wilhelm described earthworms as "the least appreciated creatures on the planet,"7 which give us fertile soil that supports the basis for agriculture and the worldwide food supply. Indeed, writing in the journal Reviews in Agricultural Sciences, researchers defined earthworms as "the most valuable animals that influence the functioning of soil ecosystems" and compiled a list of their many gifts to soil, including:8

Increase bulk density

Increase pore size

Increase water content

Increase water infiltration rate

Increase water-holding capacity

Increase litter decomposition

Increase soil organic matter dynamics

Increase nutrient cycles

Promote plant growth

Reduce some soil-borne diseases

Produce organo-mineral biogenic structures

Influence gaseous composition in the atmosphere

Restoring ecosystems, especially when soil is degraded or after mining

Enhanced microbial activity

Increase of nutrient availability in soil

Increase of mineral absorption by plants

Increase crop productivity

There are thousands of earthworm species, each with its own unique role to play — and many species that have yet to be discovered. Earthworm diversity is under threat, however, even as very few species have been extensively studied. At this time, the effects of herbicides and other agricultural chemicals on earthworms are also unknown.

There have been some advances made toward earthworm protections, specifically a mapping of earthworm communities in Europe, which is being used to raise awareness about earthworm distributions across Europe.9 However, widespread awareness of earthworms' importance to soil health and ecosystems is lacking.

The Reviews in Agricultural Sciences study researchers suggested that "dissemination of knowledge on earthworm diversity conservation to farmers needs to be prioritized because they are the direct 'actors' in agricultural activities."10 Practices such as reduced or minimum tillage, planting of cover crops and mixed farming may help both soil quality and earthworm populations to recover.

How to Increase Earthworms in Your Soil

If you're a backyard gardener and you'd like to increase the earthworms in your soil, check out the Huws Nursery video above. It gives tips on how to increase the organic matter in your soil and thereby create a more favorable environment for earthworms. If you're interested in a DIY project, The Able Gardener video below also shows how you can make a simple worm tower using a 5-gallon bucket.