The Impact of Soil pH on Earthworm Diversity and Abundance: A Systematic Review of Soil Acidity and its Effects on Vermicommunities

Soil pH profoundly affects earthworm diversity, density, biomass, and reproduction and, in turn, soil health and ecosystem process. The current systematic review, grounded on 10 peer-reviewed articles, uncovers that earthworm populations thrive best in soils with a slightly alkaline or neutral pH level of 6.5–7.5, as it favors the highest microbial activity, decomposition of organic matter, and nutrient availability. Conversely, acidic soils (pH < 5.5) significantly decrease earthworm density and diversity because of aluminum toxicity, calcium deficiency, and inhibited enzymatic activities, affecting metabolism, burrowing, and reproduction. Extremely acidic soils (pH < 4.5) cause species richness losses of 85%, biomass reductions of 70%, and cocoon production losses of 50–70%, greatly affecting soil fertility. Although moderately alkaline soils (pH > 7.5) continue to support earthworm populations, there are slight declines as a result of reduced microbial decomposition and changed soil chemistry. Reversing soil acidification requires the use of lime, organic amendments, less acidifying fertilizers, and sustainable agriculture practices. Degraded soils can also be restored and earthworm populations and biodiversity can be supported through the use of conservation tillage and phytoremediation. This review emphasizes the close relationship of soil pH with vermicommunity structure and recommends active soil management in agriculture, forestry, and conservation for the maintenance of ecosystem resilience.