The role of earthworms in agronomy: Consensus, novel insights and remaining challenges

Earthworms have a prominent role in supporting soil functioning and thus in providing key services to humanity. Their beneficial role relates to effects on soil structure, carbon and nutrient cycling as well as the soil microbial community. Optimizing the role of earthworms in agricultural systems is therefore crucial for maintaining or improving soil quality and supporting a more sustainable, circular agriculture. Here, we summarize established knowledge on the role of earthworms in agronomy; present novel insights from the past decades; and identify key knowledge gaps to be addressed in the future to fully benefit from earthworms in our agricultural soils. We start by discussing how earthworms affect basic soil processes through their effects on soil structure, microbial communities and biogeochemical cycles. Further, we show how as a result of these changes, earthworms indirectly affect plant growth, the soil greenhouse gas balance and play a role in remediation of contaminated arable soils. We further address one of the paradoxes of earthworm ecology: that they are often not present in the soils where they are most needed. We subsequently discuss potential solutions to this paradox. Finally, we identify 10 key questions that need to be addressed in the near future. In our view, recognizing that earthworms are not a stand-alone solution to improving the sustainability of cropping systems, but an essential piece of the puzzle is crucial for optimizing the benefits they offer in agronomic systems. By managing our earthworm populations well, we manage our soils well.