CHANGES IN POTASSIUM AVAILABILITY AND OTHER SOIL PROPERTIES DUE TO SOIL INGESTION BY EARTHWORMS

An incubation experiment was conducted to study the changes that occur in potassium availability and other soil properties with ingestion of soil by earthworms. Two soils were used. Raumai soil with high non-ex changeable K and Milson soil with low non-exchangeable K were incubate d with two species of earthworm, Aporrectodea caliginosa and Lumbricus rubellus, for 8 weeks. The casts and soil samples were analysed for e xchangeable K, Ca, Mg, Na, and H, pH, organic C, and texture. The resu lts indicated that in Raumai soil, the exchangeable K levels of the ca sts of both earthworm species were significantly higher than for the c ontrol soil, the effect being more marked for L. rubellus than for A. caliginosa. In Milson soil, the exchangeable K levels were significant ly lower in the casts of both types of earthworm than in the control s oil. The nitric acid-extractable K of the soil and casts was not marke dly different for either soil type, but available non-exchangeable K v alues were significantly higher for the casts of L. rubellus from Mils on soil than for the non-ingested Milson soil. In Raumai soil, the exc hangeable Ca was higher in the casts of L. rubellus, exchangeable Mg a nd H were reduced, and exchangeable Na did not change markedly in the cast compared to the control soil. For Milson soil, the casts containe d lower exchangeable Ca and H but higher Na and Mg than the control. T he casts of both species of earthworm had significantly higher pH valu es for both soil types. There was no marked difference in the organic C content of the control soil and cast samples for Milson but a reduct ion in the casts of A. caliginosa for the Raumai soil. Finer fractions increased in the casts of both earthworm species in both soil types.