Large-scale organic farming enhances soil properties and earthworm communities in relation to conventional farming in the Pampas region of Argentina

Organic farming is considered with the potential to reduce the impact on soil and its biological communities, in comparison to conventional agriculture. Organic farming primarily seeks to promote the biodiversity and functionality of soil, thereby reducing the reliance on external inputs. Earthworms have a crucial role in nutrient cycling and soil aggregation, and thus their conservation is essential in any strategy to maintain soil health and improve agricultural sustainability. In this contribution we aim to assess the differential impact of large-scale organic and conventional farming on earthworm communities and soil properties, in comparison with natural grasslands in the Pampas region of Argentina. A total of twenty-five sites were sampled, including large-scale organic (Org) and conventional (Con) non-experimental sites, and natural grasslands (Gra) used as reference. The Gra had the highest content of mineral-associated organic matter, and together with Org, had the highest content of particulate organic matter (POM) and the lowest bulk density, in comparison to Con. The highest abundance, biomass and species richness of earthworms were observed in Gra, followed by Org, and in both cases were higher than in Con. The Gra and Org showed the highest species diversity and the lowest dominance, while Con showed the opposite pattern. The earthworm communities of Gra and Org exhibited greater similarity to each other than the Con communities. A strong positive correlation was observed between soil POM and the species Microscolex dubius (Fletcher, 1887), Aporrectodea rosea (Savigny, 1826) and A. trapezoides (Duge`s, 1828), which are primarily associated with the Gra and Org sites. The results indicate that organic farming has a positive impact on soil health, as evidenced by increases in the abundance, biomass, richness and diversity of earthworms, soil POM content and porosity, as well as preserves earthworm communities that are more similar to those of grasslands than of conventional farming. The relevance of these findings is further reinforced by the fact that the organic farms under study are large-scale farms surrounded by conventional agriculture landscapes.