Activated dolomite phosphate rock fertilizers to reduce leaching of phosphorus and trace metals as compared to superphosphate.

Use of water-soluble phosphorus (P) fertilizers such as superphosphates (SP) has been increasingly concerned due to the loss of P and trace metals such as cadmium (Cd) into the environment. Activated phosphate rock holds promising as an alternate due to non-destructive and slow release nature. The objective of this study was to assess the leaching potential of P and trace metals from newly developed activated dolomite phosphate rock (HA-DPR and SLS-DPR), as compared to water-soluble fertilizers, including superphosphate (SP), diammonium phosphate (DAP) and original dolomite phosphate rock (DPR). Two representative agricultural soils (Alfisol and Spodosol soil) were sampled at the 0-20 cm depth from two farms for the column leaching experiments. Seven leachings were conducted at day 1, 3, 7, 14, 21, 28, and 56, respectively, and a total of 1050 mL of deionized water (equivalent to half year's rainfall in the Indian River area) was applied for leaching. Leachates were collected from each leaching event and analyzed for water-soluble P and metals. Activated DPR application led to an increase in soil pH by 1.4-1.7 units, whereas SP resulted in a decrease in soil pH by 0.4-1.6 units. P leaching from activated DPR were 33-61 times less than that from SP or DAP. HA-DPR and SLS-DPR treatments reduced cumulative trace metals in leachate by 1.3-12.3 times for the Alfisol soil, and 1.4 to 8.4 times for the Spodosol soil, respectively. These results indicate that activated DPR fertilizers are more environmentally friendly than water-soluble fertilizers.