The exchangeable calcium in the soil showed a similar behavior to the other elements previously discussed with respect to sampling times, indicating that, during the crop cycle, the sunflower plants absorbed calcium provided by the waste water. Exchangeable calcium levels above 0.4 cmolc dm−3 are considered suitable for the cultivation of sunflower [18], showing that the concentration of exchangeable calcium in the soil was high, probably due to fertilization with organic waste completed in previous crops.