Yield, nutrient uptake and potassium use efficiency in rice fertilized with crushed rocks

The increasing world population has led into big food and raw material demand, with high pressure on agriculture. In Brazil, potassium fertilizers are mostly imported rising interest on rocks and mining rejects as alternative sources. The objective of this work was to evaluate the effect of crushed rocks over mineral nutrition, yield and efficiency of potash fertilization in rice. The experiment was carried out under greenhouse conditions in pots with 3.7 kg of Oxisol soil samples. The experimental design was completely randomized, in a factorial layout 4 × 6, comprising six crushed rocks used as alternative multinutrient fertilizer (breccia, biotite schist, ultramafic, Chapada byproduct, mining byproduct and phlogopite), and four doses based on potassium (0, 200, 400, 600 kg K2O ha-1), with four replications. The concentration and accumulation of potassium, copper, zinc and nickel in rice shoot dry mass were determined. These data were used to evaluate the efficiency index of K-source rocks on fertilization. It was shown that crushed rocks promote alterations in mineral nutrition, grain yield and potassium use efficiency, remarking their potential to be used as alternative fertilizer in rice cropping systems.   Key words: Alternative nutrient source, micronutrient, fertilization efficiency, plant nutrition, soil conditioner.