Replacing calcareous soils with acid soils to grow rainforest species at Fairchild Tropical Garden, Miami

The objective of this investigation was to examine pH changes of three acidic soils (silica sand soil, red clay soil and a mixed soil) used to establish tropical plants in a rainforest exhibition at Fairchild Tropical Garden, Miami, Florida. The three areas were excavated to remove native calcareous soil and filled with acidic soils. Various rainforest plants were planted. Soil samples were collected vertically every 10 cm from soil surface to bedrock shortly after filling and one year later. Soil pH and EC were determined. Results showed that both silica sand and mixed soils had been neutralized and the soil pH values were over 7 at all soil depths after one year. However, less than 10 cm surface and bottom soil layers of red clay soil were neutralized, and the soil pH in the middle of soil profile was unchanged due to the higher buffering capacity. It is likely that acidity of red clay soils would not last very long with the addition of calcium carbonate to soils by irrigation, capillary movement from groundwater and runoff from uphill.