Successive off take of elements by maize grown in pure basalt powder

Basalt powder wastes from mining activities have potential to be used as a natural fertilizer. Basalt minerals in agricultural soils may release plant nutrients and increase soil negative charge. In this work, the weathering of basalt promoted by maize rhizosphere was investigated. We studied the chemical and mineralogical composition of basalt, including cation exchange capacity, as well as the rate of elements offtake by maize grown in a pure basalt powder during seven successive growth cycles. A pot experiment was carried out under controlled environmental conditions; plant and rock materials were evaluated at the end of successive growth cycles. X-ray powder diffraction analysis showed diopside and andesine as main minerals of basalt, and smectite. Scanning electron microscopy images evidenced new amorphous components resulting from rhizosphere-induced weathering. The elements K, Ca, Mg, Al, B, Cu, Fe, Mn and Zn were measured in plant tissue, and related to the weathering of basalt minerals. The studied basalt, therefore, provides nutrients to plants and exhibits physicochemical properties, such as cation exchange capacity, especially important for highly weathered soils presenting low cation exchange capacity, such as Oxisols. Key words: Bioweathering, natural fertilizer, mining waste, basalt minerals, cation exchange, nutrient availability.