The concentration and molar percentage of water-soluble
Ca2+ for all treatments were compared after 6 months and
18 months (Table 2). After 6 months, the concentrations of
Ca2+ significantly increased with FGD-gypsum application
rate in the 0–10 cm soil layer by 2.63–15.9 cmol/kg compared
with the control, and the molar percentages were increased by
5.76–18.2 times, correspondingly. The concentrations of Ca2+
in the 45 and 60 Mg/ha FGD-gypsum treatments significantly
increased by 1.46 and 3.09 cmol/kg in the 10–20 cm soil
layer, respectively, and significantly increased by 0.27 and
0.35 cmol/kg in the 20–30 cm soil layers, respectively. Only the
molar percentage of Ca2+ in 60 Mg/ha FGD-gypsum treatment
significantly increased in both 10–20 cm and 20–30 cm soil
layers, which increased by 6.29 times and 1.26 times,
respectively. Similar trends occurred after 18 months of
FGD-gypsum application, except for the difference that the
concentrations of Ca2+ in all FGD-gypsum treatments significantly
increased in the 10–20 cm soil layer after 18 months,
and the molar percentages in both 45 Mg/ha and 60 Mg/ha
FGD-gypsum treatments increased in the 10–20 and 20–30 cm
soil layers. The Ca2+ increase resulted from the dissolution of
the FGD-gypsum