Evaluation of phosphorus leaching from contaminated calcareous soils due to the application of sheep manure and ethylenediamine tetraacetic acid

Organic amendment application to heavy metal contaminated soils may contribute to leaching of phosphorus (P). The objectives of this study were to determine the influence of sheep manure and ethylenediamine tetraacetic acid (EDTA) on the P leaching from a wide range of calcareous contaminated soils. Glass tubes, 4.9 cm diameter, and 40 cm long, were packed with contaminated soil. The resulting 20 cm long column of soils had bulk density of 1.3–1.4 g cm⁻³. The columns were leached with distilled water, 0.01 M EDTA, 0.01 M CaCl₂ or sheep manure extract (SME) solutions. The breakthrough curves for P were different and the amounts of P leached varied considerably between different soils and leaching solutions. The amounts leached with SME were less than the amount added through the SME, indicating that some P was retained by the soil, mainly due to preliminary sorption of organic ligands on to the soil with the creation of new sorbing surfaces. The amount leached with EDTA solution varied from 9.9 to 46.3% of the extractable P when 15 pore volumes had passed through the column. Low amounts of P were leached by 0.01 M CaCl₂, which is likely to be due to the high concentration of soluble Ca used in the solution. Thus, among leaching solutions the application of EDTA and SME on contaminated calcareous soils might enhance the mobility of P and large amounts of P will be leached, leading to contamination of ground and surface waters.