Earthworms mediate the effect of diversifying crop rotations on soil organic carbon incorporation, soil structure formation and microbial activity

Diversifying crop rotations aims to improve soil fertility and productivity. In many farming systems earthworms offer great promise to help achieve this goal, due to their impacts on soil organic matter dynamics, nutrient cycling, and soil structure. We assessed the effect of diversifying crop rotations on the contribution of earthworms to soil organic carbon incorporation, structure formation, and microbial activity regulation. We conducted a microcosms experiment for 15 days, with each microcosm containing 5 individuals of Aporrectodea caliginosa and 20 g of different crop residue combinations representing common crop rotation schemes in the Pampas: no residue (NR), soybean (S), soybean plus maize (SM) and vetch, maize and soybean (VMS). A. caliginosa produced 40–135 % fewer casts in VMS (p < 0.0001), but these, along with those in SM, had 36 % and 25 % more coarse particulate organic carbon than bulk soil, and 100–165 % more than NR and S casts (p < 0.0001). Casts in SM had 23–42 % more fine particulate organic carbon than casts in the other treatments and 42 % more than bulk soil (p = 0.0002). Additionally, casts in VMS and SM, had 35–70 % higher mean weight diameter (p < 0.0001) and 30–1400 % higher proportion of water-stable earthworm macroaggregates compared to S and NR (BMa: p < 0.0001; SMa: p = 0.0235). Casts in VMS had higher α-glucosidase (39 %) (p < 0.0001), β-glucosidase (220 %) (p < 0.0001), phosphomonoesterase (48 %) (p < 0.0001) and N-acetyl-glucosaminidase (36 %) (p = 0.0008) activity than bulk soil, and higher β-glucosidase (70–134 %) (p < 0.0001), cellobiohydrolase (30–500 %) (p < 0.0001) and phosphomonoesterase (60–340 %) (p < 0.0001) activity than casts in other treatments. We conclude that diversified crop rotations enhance earthworm-mediated soil functions, improving aggregation, stubble decomposition, and organic matter stabilization. This fosters biologically active, structurally stable soils, boosting fertility and long-term agricultural sustainability in the Pampas.