Cover crops and soil ecosystem engineers

Earthworms are key to the engineering of soil ecosystem services. However, how cover crops (CCs) influence these ecosystem engineers has not been widely discussed. This paper reviews (a) CC effects on earthworm abundance, biomass, diversity, and related soil ecosystems services and (b) factors affecting CC effects on earthworms. A review of existing literature (through 29 May 2022) found 22 CC studies on earthworm abundance and 10 on earthworm biomass, but studies on earthworm diversity were few. Cover crops increased earthworm abundance in 13 of 22 studies, increased biomass in five of 10 and had no effect in the rest of studies compared with no CCs. The change (Delta increase) was 11 to 535 earthworms m(-2) and 11 to 44 g of earthworm biomass m(-2). Cover crop effects on earthworm diversity are mixed. Earthworm abundance was more responsive to CCs than soil C and physical properties, suggesting earthworm abundance should be included as a sensitive measurement in soil health status. Cover crops with low C/N under no-till or reduced-till systems promote earthworm abundance relative to CCs with high C/N under conventionally tilled systems. Cover crop mixtures do not increase earthworm abundance more than monocultures. Earthworm abundance generally increases with increasing precipitation (r = 0.45; p =.025) and temperature (r = 0.36; p =.10). Overall, CCs increase earthworm abundance but have mixed effects on earthworm biomass and diversity, although more data from different CC management scenarios and climates are needed for more robust conclusions.