Impact of 60 Years of Intensive Rice Cropping on Clay Minerals in Soils Due to Si Exportation

Rice is cultivated as staple for over half of the World’s population. In Camargue (South of France) rice fields have been established on very young soils developed from historic fluvial deposits of the Rh？ne River. The comparison of clay mineralogy in a paddy field cultivated for 60 years and in a control shows a significant increase of the clay crystallinity in the paddy field soil, which implies a decrease of their solubility. In the paddy soils, phytoliths, poorly crystallized clays, such as smectite and to a lesser extent kaolinite, are progressively dissolved to supply Si for rice requirements. The sustainability of the crop system requires the clearing of silica exportations.