Mineralogia, química, eficiência agronômica e tecnologias de solubilização de agrominerais fontes de potássio

Abstract

The higher brazilian fertilizers consumption and dependence on the importation of potassium fertilizers, suggests the need to study the feasibility of alternative sources of nutrients. This study aimed to identify potential alternative sources of potassium based on studies of mineralogical characterization of rocks, evaluation of these on growth of millet and study the solubilization of rocks using different extractors, times and temperatures of reaction. The rocks characterized using thin-section petrographic description, X-ray diffraction, lithogeochemical analysis, and analysis of their solubility with the use of different extractors. An experiment was conducted with the use of soils that differ on texture and mineralogy: Red Oxisol (RO), Red Yellow Oxisol (RY) and Quartz-Sand Neosol (QN). The aerial part dry mass (APDM) and chemical analysis determination for both cultivations and agronomic efficiency of the tested rocks were evaluated. In the solubilisation experiment were tested Ammonium dihydrogenphosphate (NH4(H2PO4)), Calcium dihydrogenphosphate (Ca (H2PO4)2), Sodium hydroxide (NaOH) and distilled water (control) as extractants. The extractants were subjected to a water bath shaker with temperature of 25°C (1st experiment) and 50ºC (2nd experiment) for periods of 3, 7, 10, 20 and 30 days of reaction. In the extracts analysis were evaluated pH, electrical conductivity, K and other rock forming mineral contents. According to lithogeochemical analysis, the glauconite and nepheline syenite rocks possess higher K2O contents. The extractants that promote higher solubilisation of potash were, in decreasing order, USEPA 3051, citric acid, nitric acid, water and CNA, where nepheline syenite presented the highest solubility values mica-schist rocks, the lowest. Higher yields of APDM were observed in the 2nd cultivation, suggesting with increasing contact rock-soil, higher residual effect of these materials. In the 2nd cultivation, for all soils, the nepheline syenite rock presented APDM superior to conventional treatments, the same occurred in treatments with mica schist rock for LV and LVA. On solubilisation experiment the reaction time and temperature influenced on K solubilised. The extractants that solubilised higher amounts of K to the rocks in the study were in descending order: NH4H2PO4> Ca(HPO4)2> NaOH> H2O. A proposal of weathering sequence of rocks, based on % K sol in descending order are: nepheline syenite> glauconita> biotite. Studies in field conditions to evaluate the residual effect of the rocks and also the effect of different extractants in the solubilization of K and other nutrients present in rocks are suggested.