Influence of fluorine content of potassium trioctahedral micas on plant availability of interlayer potassium and effectiveness to reduce radiocesium uptake by paddy rice

Characterization of 10 potassium trioctahedral micas alongside pot cultivation of paddy rice was conducted here to elucidate the influence of F content on the plant availability of non-exchangeable K in the interlayers of these micas. Additionally, their effectiveness as soil amendments in reducing radiocesium uptake by paddy rice was investigated. Chemical analysis confirmed that all micas were potassium trioctahedral type, whilst F content varied between 0.09 and 1.24 per half-unit cell. The application of potassium trioctahedral micas did not increase soil exchangeable K before planting; however, exchangeable K after harvest was higher in mica-amended pots than in control pots, except for two micas. This indicated the release of non-exchangeable K during the growing season of paddy rice. Furthermore, the soil K status during the later growth stage was reflected by higher K uptake by rice shoots and lower radiocesium transfer to brown rice compared with the control, thus suggesting the effectiveness of phlogopite and biotite as soil amendments for increasing K uptake by paddy rice, whilst reducing radiocesium uptake. The strong positive correlation of tetraphenylborate-extractable K with soil K status during the late growth stage with K uptake by rice shoots suggested that the plant availability of non-exchangeable K in potassium trioctahedral mica amendments could be evaluated through tetraphenylborate extraction. An increase in the F content of Fe-poor potassium trioctahedral micas resulted in decreased soil K status during the late growing season, alongside decreased K uptake by shoots and increased radiocesium transfer to brown rice. However, the negative influence of F on the plant availability of non-exchangeable K appeared to be less significant in Fe-rich potassium trioctahedral micas than in Fe-poor ones.