Brazil is dependent on importation of fertilizers, especially the potassics. Rocks and minerals that contain nutrients have a potential for use in agriculture as fertilizer, especially those of slow solubilization and that exhibit residual effect. In this context, the objective was to assess the feasibility of glauconite rock as potassium source for the cultivation of ornamental sunflower. The experiment was conducted under controlled conditions arranged in an entirely randomized design, in a 4x4 + 4 factorial scheme, with four replicates and one plant per plot. Four glauconite-based fertilizers were used as a potassium source: fine grained glauconite, fine grained organo-mineral glauconite, coarse grained glauconite and coarse grained organo-mineral glauconite, in four doses, as well as an additional treatment with four doses of KCl, the principal conventional source of the nutrient. The height of the flower stalks, the diameter of the stem and floral capitulum, the number of cultivation days and post-harvest durability were evaluated. The application of KCl yielded the production of flower stems with greater height and larger capitulum diameter in relation to the supply of glauconite. Among the glauconite based fertilizers, the fine grained organo-mineral product provided the best flower charateristics. The postharvest commercial durability of the flower stalks was higher in plants that received the glauconite and fine grained organo-mineral glauconite. The fine grained organo-mineral glauconite surpasses all other alternative sources of potassium in relation to the agronomic characteristics evaluated.
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