Glauconitic Siltstone as a Source of Potassium, Silicon and Manganese for Flooded Rice

The objective of this study was to evaluate the efficiency of glauconitic siltstone as a multi-nutrient source for flooded rice. Two experiments were carried out under greenhouse conditions, one using a Ferralsol and the another an Arenosol. Glauconitic siltstone was applied in different doses (0, 5, 20, 40, and 80 mg dm-3 K2O) and potassium chloride, wollastonite, and manganese sulfate were respectively used as standard sources, at doses of 80 mg dm-3 K2O, 270 mg dm-3 Si, and 2 mg dm-3 Mn. The sources were incubated for 90 days on the two soil types and, after the incubation period, rice plants were sown, and two consecutive rice growths were performed. The application of glauconitic siltstone in tropical soils promotes increases in the plant and grain dry matter of rice plants, as well as K, Si and Mn contents in soil samples and accumulated in plants. Greater effects following the application of glauconitic siltstone are obtained after the second rice growth due to its gradual release.