Use of Activated Dolomite Phosphate Rock to Reduce Leaching of Phosphorus and Heavy Metals in Sandy Soils.

Beneficial use of medium- and low-grade phosphate rock (PR) is necessary to overcome shortage of high-grade phosphate rock resource worldwide. Previous studies indicated that activation of dolomite PR (DPR), with selected organic molecules resulted in substantial increases in water soluble phosphorus (WSP), by 10-100 times. In this study, column leaching experiments were conducted to evaluate environmental impacts of activated DPR with regards to leaching potential of P and other elements, especially heavy metals, which are concerned due to their potential risks to human health. Two representative agricultural soils (Spodosol and Alfisol) in south Florida were used to compare the activated DPRs with water soluble fertilizers including diammonium phosphate (DAP) and superphosphate (SP) made from the DPR materials. The soils amended with different P fertilizers were incubated at room temperature with 70 % field water holding capacity for 14 days before packed into PVC columns and subjected to leaching. The leaching were conducted at day 1, 3, 7, 14, 21, 28, and 56, respectively. At each leaching event, 150 mL of deionized water was applied using a peristaltic pump, with a total of 1050 mL, which is equivalent to half year’s rainfall in the Indian River area (average of 2015-2016). Leachate solutions were collected for each leaching event and analyzed for pH, EC, dissolved organic carbon (DOC) and total soluble elements (P, Ca, Mg, K, Na, Fe, Mn, Al, Cu, Zn, Cd, Ni, Cr, Co, Pb). Application of activated DPR fertilizers resulted in reduced cumulative leaching losses of heavy metals and P as compared to SP and DAP.

Key words: Contaminant, mineral, nutrients, slow release fertilizers