Use of amendments to reduce leaching loss of phosphorus and other nutrients from a sandy soil in Florida

Goal, Scope and Background Transport of P from agricultural land contributes to the eutrophication of surface waters. Soil amendment is considered one of the best management practices (BMPs) to reduce P loss from sandy soils. Laboratory column leaching experiments were conducted to evaluate the effectiveness of different soil amendments in reducing P leaching from a typical sandy soil in Florida. Methods The tested amendments were CaCl₂, CaCO₃, Al(OH)₃, cellulose, and mill mud, and applied at the rate of 15 g/kg for a single amendment and each 7.5 g/kg if two amendments were combined. Leaching was conducted every four days for 32 days, 250 mL of deionized water being leached for each column per leaching event. Leachates were collected from each leaching event and analyzed for reactive P, PO₄-P, and macro and micro-elements. Results and Discussion Except for the soils amended with CaCl₂, or CaCl₂+CaCO₃, reactive P and PO₄-P leaching losses mainly occurred in the first three leaching events. Phosphorus leaching from the soils amended with CaCl₂ or CaCl₂+CaCO₃ was less but more persistent than that of other amendments. Reactive Pleaching loss was reduced by 36.0% and 40.4% for the amendments of CaCl₂, and CaCl₂+CaCO₃, respectively, as compared with chemical fertilizer alone, and the corresponding values for PO₄-P were 70.8% and 71.9%. The concentrations of K, Mg, Cu, and Fe in leachate were also decreased by CaCl₂ or CaCl₂+CaCO₃ amendment. Among the seven amendments, CaCl₂, CaCO₃, or their combination were most effective in reducing P leaching from the sandy soil, followed by cellulose and Al(OH)₃, the effects of mill mud and mill mud + Al(OH)₃ were marginal. Conclusions These results indicate that the use of CaCl₂, CaCO₃, or their combination can significantly reduce P leaching from sandy soil, and should be considered in the development of BMPs for the sandy soil regions. Recommendations and Outlook Most agricultural soils in south Florida are very sandy with minimal holding capacities for moisture and nutrients. Repeated application of fertilizer is necessary to sustain desired yield of crops on these soils. However, eutrophication of fresh water systems in this area has been increasingly concerned by the public. Losses of P from agricultural fields by means of leaching and surface runoff are suspected as one of the important non-point contamination sources. The benefits and effectiveness of soil amendment in reducing P losses from cropping production systems while sustaining desired crop yield need to be demonstrated. Calcium chloride, CaCO₃, or their combination significantly reduce Pleaching from sandy soil, and should be considered in the development of BMPs for the sandy soil regions.