Earthworm- and Rhizosphere-Induced Biological Weathering of Phlogopite

© 2021, The Author(s) under exclusive licence to Sociedad Chilena de la Ciencia del Suelo.Biological weathering of soil minerals is important from soil fertility and soil evolution points of view. Little information is available on the interaction influence of earthworm and rhizosphere on soil mineral bio-weathering and nutrient release. The objectives of this investigation were (a) to examine if earthworm could alter phlogopite (a micaceous mineral) and (b) to study root-induced weathering and potassium (K) release. A mixture of cow manure and phlogopite was incubated with or without the earthworm Eisenia fetida for two time periods of 3 and 6 months to produce enriched vermicompost and compost, respectively. A greenhouse pot experiment was then carried out where barley was grown for 2 months in the pots containing phlogopite-enriched vermicompost or compost produced in the first experiment. Mineralogical changes in phlogopite and also selected chemical properties were evaluated. The results showed a significant effect of earthworm activity and incubation period on phlogopite weathering, C/N ratio (from 24.3 to 13.9), available K (from 1.24 to 1.34%), and HNO3-extractable K (from 2 to 2.4%). The highest dry weight and the concentration and uptake of K were found in the plants cultivated in vermicompost incubated for 6 months. Also, the results indicated that under the incubation conditions, earthworm activities resulted in the dominance of the vermiculitization process. In contrast, transformation to smectite was dominant in the barley rhizosphere. Earthworm activities accelerated the rate of mineral transformation and element release, which led to an increase in the available form of elements. Such an element release was also enhanced in plant rhizosphere, which consequently increased the yield.