A thermodynamic evaluation of the addition of calcium and magnesium to an Ultisol: II CaS04 addition

Abstract

An 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 SO₄^2- can not prevent the fixation of magnesium, and that aluminum and pH might be the controlling factors of said mechanism.