Changes in soil mineralogical properties in humid subtropical regions due to potassic fertilizer practices are so far poorly understood. The main objective of this study was to compare the changes in soil minerals and the consequences on K+ release. Soil samples (depth of 0-10 cm) were collected over eleven years from areas with and without K fertilization and from a nearby natural grassy vegetation site on the Campus of the Federal University of Santa Maria. The K fertilizer treatments were 0 kg ha-1 year-1 of K2O (K0) and 90 kg ha-1 of K2O year-1 of K2O (K90). The total K+, non exchangeable K+ and exchangeable K+ were determined in the soil samples. Feldspats, illite and interstratified illite-smetite minerals were identified in X ray diagrams of Ca2+-saturated soil and clay fractions. The K90 treatment appeared to preserve the illite and illite-smectite interstratified minerals in the clay fraction. Independent of the level of potassic fertilization, the illite and illite-smectite mineral proportions tended to decrease at the expense of interstratified hydroxy-Al vermiculite.
K+ selectivity; X ray diffraction; interstratified minerals; mica
