Potassium (K) is one of the most absorbed nutrients by forage plants and it is found at low levels in tropical soils, requiring large amounts of fertilizers. The use of glauconitic siltstone as multi-nutrient fertilizers is an economic alternative to improve pasture-based production systems due to their low-cost production and long-term nutrient release. This study evaluated the effect of the glauconitic siltstone (GS) powder on three successive crops of Urochloa brizantha cv. Marandú (Syn. Brachiaria brizantha). Two experiments were carried out under greenhouse conditions, one using a Typic Dystrustox and the other a Typic Quartzipsamment. Both experiments were arranged in a completely randomized design with one factor, i.e., five glauconitic siltstone doses (0, 5, 20, 40, and 80 mg dm-3 of K2O) and four replications. In addition, three additional treatments were used, as potassium chloride, wollastonite and manganese sulfate at doses of 80 mg dm-3 of K2O, 270 mg dm-3 of silicon (Si) and 2 mg dm-3 of manganese (Mn), respectively. The sources were incubated for 60 days on the two soil types and, after the incubation period, Urochloa brizantha plants were grown. Three consecutive cuts were performed at 68, 104 and 168 days after sowing. The application of the GS in tropical soils promoted increases in plant dry matter, as well as K, Si and Mn levels in soil samples and accumulated in plants. In general, greater effects were obtained following the application of GS after consecutive cropping cycles due to its long-term release. Results described in this study provide an important understanding of the use of glauconitic siltstone as multi-nutrient fertilizers in tropical soils, being an efficient alternative to improve soil fertility and increase tropical pasture productivity.

Agradeço a Deus, por ter me proporcionado saúde, proteção e força para superar todos os desafios desta etapa. Ao orientador, Professor Dr. Hamilton Seron Pereira, pelos ensinamentos compartilhados, orientação, atenção e ajuda durante a elaboração da dissertação e pelo exemplo de profissional. A todas as pessoas do Laboratório de Tecnologia de Fertilizantes (LAFER) e também aos integrantes do Grupo de Pesquisa sobre Silício na Agricultura (GPSI), que me auxiliaram para que a realização desse trabalho fosse possível. Em especial, a Luiz