Populations of earthworms are being severely harmed by a common farming practice.

The humble earthworm is essential to healthy soil. Photo: Shutterstock

You may not think much about earthworms, but they are crucial to healthy soil. In fact, Charles Darwin called them “nature’s plough” because they are constantly eating and defecating soil, making it more nutritious and better aerated—and therefore more fertile.

But a widely used farming practice is severely damaging those earthworm populations.

Tillage farming, also known as conventional plowing, is harming earthworms all around the world. The deeper the soil is disturbed, the more it harms the earthworms.

A team of scientists recorded this data by analyzing 215 field studies from 40 countries, dating back some 70 years. Each of the studies examined earthworm populations under tillage farming and other forms of reduced tillage.

“What we see is a systematic decline in the earthworm population in the soil after continued plowing 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,” said researcher Prof. Olaf Schmidt of University College, Dublin.

The study shows that the earthworms most vulnerable to tillage are anecic earthworms—larger worms that move between topsoil and subsoil and create permanent burrows there. Epigeic earthworms, small worms that live in the topsoil and convert debris to topsoil, are also susceptible to plowing.

However, farming practices such as conservation agriculture and shallow non-inversion tillage were actually shown to significantly increase earthworm populations. These practices are being adopted around the world because of their environmental benefits such as erosion control and soil protection.

The research revealed that the herbicide glyphosphate, which has caused a great deal of controversy, did not have a significant effect on earthworm population responses to reduced tillage.

Professor Maria Briones of the University of Vigo said, “Switching to reduced tillage practices is a win-win situation for farmers because they save costs and in return larger earthworm populations help in soil structure maintenance and nutrient cycling.”