The objective of this study was to evaluate the reactivity of four Si sources: schist, two types of slag and a thermal-phosphate based on Si availability in the Typic Eutrustults and in the tomato crop uptake. Two experiments were carried out in a randomized block design with the following treatments: check plot, 6 t ha-1 of schist, 6 t ha-1 of Mannesman slag, 6 t ha-1 of Dedini slag and 2.5 t ha-1 of thermal-phosphate. The Si content (SiO2 total) in the products was: schist 530 g kg-1, Mannesman slag 350 g kg-1, Dedini slag 273 g kg-1 and thermal-phosphate 185 g kg-1. Silicon levels in the soil, extracted by ammonium oxalate, were highest in the Mannesman slag treatment, while the schist treatment presented the lowest levels. The relationship among Si application and Si in the soil, however, showed that thermal-phosphate was more efficient compared to the others Si sources. The applied Si sources were able to provide Si for the tomato, but were insufficient to increase yields. A good correlation was observed between the Si plant content and Si extracted with ammonium oxalate from the soil.
schist; slag; thermal-phosphate; tomato
