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 specie s of earthworms viz., Aporrectodea caliginosa and Lumbricus rubellus, to study the influence of soil ingestion by earthworms on the concentr ations 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 highe r in Tokomaru (rolling phase), Tokomaru (virgin) and Timaru soils, and that L. rubellus was more effective than A. caliginosa in all the soi ls studied. In Marton soil, exchangeable K+ concentrations of the cast s of A. caliginosa were not markedly different from the non-ingested s oil. 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 sign ificantly by the exchangeable and step K values of the soils used in t his study (R2 = 1.00 and 0.998 for A. caliginosa and L. rubellus respe ctively). The concentrations of exchangeable Ca2+ Mg2+, and Na,+ of th e 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 soi l.