SAARELA, I., A. JÄRVI, and H. HAKKOLA. “Phosphorus Status of Diverse Soils in Finland As Influenced by Long-Term P Fertilisation 2.Changes of Soil Test Values in Relation to P Balance With References to Incorporation Depth of Residual and Freshly Applied P”. Agricultural and Food Science, vol. 13, no. 3, Jan. 2004, pp. 276-94, doi:10.2137/1239099042643099.