Scientists from University College Dublin and the University of Vigo, Spain, have found that the digging, stirring and overturning of soil by conventional ploughing in tillage farming is severely damaging earthworm populations around the world.

The findings, published in the scientific journal Global Change Biology, show a systematic decline in earthworm populations in soils that are ploughed every year.

The deeper the soil is disturbed the more harmful it is for the earthworms.

Scientists from the two universities examined 215 field studies from across 40 countries, dating back as far as 1950. Each of the studies investigated earthworm populations under conventional tillage and other forms of reduced tillage.

“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,” reported Associate Professor Olaf Schmidt, from the School of Agriculture and Food Science, University College Dublin.

According to the findings, anecic earthworms are most vulnerable to tillage; they are large earthworms that move between layers of soil and create permanent burrows between them. Small earthworms, called epigeic earthworms, that live in the top layers of soil and convert debris to topsoil were also found to be highly susceptible.

Earthworms play a pivotal role in maintaining the productivity of our soils. Their burrowing and feeding activity has numerous beneficial effects on overall soil quality. Charles Darwin referred to them as “nature’s plough”.

Shallow non-inversion tillage was shown to significantly increase earthworm populations. Reduced tillage practices are increasingly being adopted due to their environmental benefits, according to the scientists.

Reduced tillage practices will restore productive earthworm populations and help maintain soil structure and nutrient recycling, they claim.

“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,” Prof. Maria Briones said.