Calcium carbonate is used to help prevent the spread of various diseases, such as powdery mildew, black spot, and blossom end rot. Calcium carbonate (as you may have guessed) bestows plants with a (1) healthy source of calcium, (2) pH balancing properties, (3) increases water retention ability within acidic soils, and (4) encourages absorption of crucial nutrients including nitrogen, potassium, and phosphorus despite being rooted in acidic soils.