AbstractAn experiment was conducted to evaluate the effects of CaS04 additions on the chemical properties of an Ultisol. Four levels of calcium and three levels of magnesium were combined in a 4 x 3 complete factorial experimental design. As expected, the addition of CaS04 resulted in significant increases in the levels of calcium in solution. Furthermore, a decrease in the amount of exchangeable magnesium was observed. This was in turn reflected in an increase in the concentration of magnesium in solution. The correlation between the amount of magnesium in the exchange phase and in solution suggests that the fixation phenomenon frequently observed in limed soils does not occur when CaS04 is used. To evaluate the effect of increases in pH in these samples, NaOH was added a month after CaS04 addition. As in the case of Ca(OH)2, a decrease in the levels of magnesium in solution was observed. This led us to conclude that the presence of SO42- can not prevent the fixation of magnesium, and that aluminum and pH might be the controlling factors of said mechanism.
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