EXCHANGEABLE POTASSIUM AND OTHER CATIONS IN NONINGESTED SOIL AND CASTS OF 2 SPECIES OF PASTURE EARTHWORMS

An incubation experiment was conducted using four soils and two species of earthworms viz., Aporrectodea caliginosa and Lumbricus rubellus, to study the influence of soil ingestion by earthworms on the concentrations of exchangeable K+ and other soil cations. Analyses of cast and soil samples for exchangeable cations revealed that the exchangeable K+ content of casts of both types of earthworm was significantly higher in Tokomaru (rolling phase), Tokomaru (virgin) and Timaru soils, and that L. rubellus was more effective than A. caliginosa in all the soils studied. In Marton soil, exchangeable K+ concentrations of the casts of A. caliginosa were not markedly different from the non-ingested soil. Increases in the values of exchangeable K+ content differed with the types of soil and earthworm used. The multiple regression analyses revealed that the differences in these values could be predicted significantly by the exchangeable and step K values of the soils used in this study (R2 = 1.00 and 0.998 for A. caliginosa and L. rubellus respectively). The concentrations of exchangeable Ca2+ Mg2+, and Na,+ of the casts of both types of earthworm tended to increase compared to the non-ingested soil. Exchangeable H+ and the cation exchange capacity of the cast material remained unaltered with respect to non-ingested soil.