Davie Mayeso Kadyampakeni, 700 Experiment Station Rd, University of Florida, Lake Alfred, FL, Peter Nkedi-Kizza, Soil and Water Sciences Department, University of Florida, Gainesville, FL, Kelly T. Morgan, Soil and Water Science Department, University of Florida, Immokalee, FL and Arnold Schumann, Citrus Research and Education Center, University of Florida, Lake Alfred, FL
Phosphorus is a critical nutrient in citrus production whose deficiency or excess can affect crop yield and quality. Sound stewardship and management of P would help growers maintain high yields, conserve environmental quality and realize high economic returns. Appropriate estimation of sorption coefficients and subsequent characterization of P movement would provide necessary information for sustainable environmental management, reduce problems of eutrophication, and prevent groundwater contamination. Laboratory experiments and computer simulations were conducted to 1) determine the effect of supporting electrolyte on P sorption coefficient (KD), 2) evaluate the effect of sorption coefficients on prediction of P movement at 30- and 60 cm soil depths using HYDRUS-1D, and 3) compare the P concentrations and fluxes as a function of irrigation frequency and soil type. Results indicate P sorption was of the order: 0.005 M CaCl2 > 0.01 M KCl ≈ fertilizer mixture [NH4NO3 + KH2PO4] suggesting an influence of the cation on P adsorption. The sorption coefficients (KD) determined using 0.005 M CaCl2 as the supporting electrolyte were about threefold greater than the KD determined in the fertilizer mixture suggesting that Ca+2 in solution might result in overestimation of P sorption on sandy Spodosols and Entisols. Model simulations confirmed the laboratory results with slower P mobility using KD estimated with 0.005 M CaCl2 than the other two supporting electrolytes. Irrigation frequency did not affect P movement in the two soils.