Influence of Eisenia fetida on aluminum fractions in latosolic red soil

Objective  To investigate the impacts of earthworms on soil acidification characteristics and aluminum (Al) fractions of latosolic red soil in South China, and provide a theoretical basis for acidification improvement of latosolic red soil in South China.

Method  The earthworms (Eisenia fetida) were incubated with latosolic red soil under laboratory conditions. After 40 days of incubation, Al fractions in earthworm cast and soil, namely exchangeable (Al_Ex), weakly organically bound (Al_Orw), organically bound (Al_Or), amorphous (Al_Amo), Al occluded in crystalline iron oxides (Al_Oxi), and amorphous aluminosilicate and gibbsite (Al_Aag) fractions, were determined using sequential extraction methods. Earthworm cast and soil pH, organic carbon, total nitrogen, and cation exchange capacity (CEC) were determined. The principal component analyses were applied to study the distribution of different Al fractions in different treated soils. And the soil without earthworm was set as a control.

Result  Compared to the control soil, pH of earthworm casts increased by 1.27, the total nitrogen, CEC, Al_Or and exchangeable K, Na, and Ca contents increased by 62.16%, 38.22%, 355.70%, 151.38%, 65.38% and 51.90%, respectively, and Al_Ex contents in earthworm casts and soil decreased by 50.95% and 53.14% respectively. The pH, CEC, Al_Or and exchangeable K, Na, Ca contents in casts were significantly higher than those in non-ingested soil.

Conclusion  Earthworms can significantly increase soil pH and Al_Or, promote the release of exchangeable Ca²⁺ and Mg²⁺, and reduce soil Al_Ex content.