Fractionation of soil phosphorus in a long-term phosphate fertilization

The changes in inorganic and organic phosphorus (P) fractions of soil resulting from long-term fertilization (40 years) were investigated. In order to improve understanding of the sink and sources of phosphorus, P-fractions were extracted from soil samples from depths of 0-30 and 30-60 cm with different amounts of monoammonium-phosphate (MAP) and then determined. The studied soil was of the Stagnosol type. Phosphate fertilizer was applied in 26, 39 and 52 kg P ha(-1) amounts during a period of 40 years. Samples were subjected to sequential extraction according to a modified Chang and Jackson method and the Community Bureau of Reference (BCR) sequential extraction procedure in order to extract different forms of phosphorus. The certified reference material CRM 684 (river sediment extractable phosphorus) was used to confirm the accuracy of the instrument and of both employed methods. Furthermore, the association of phosphorus with substrates was provided by comparison of the results of sequential methods of phosphorus species with the sequential extraction of metals (Fe, Al, Mn and Ca). The results of continuous fertilization during 40 years indicated increases of all forms phosphorus in the soil except of phosphorus bound to calcium and organic phosphorus. Application of higher amounts of P-fertilizer resulted in the dominance of the Al P fraction in the studied soil, which indicated that this fraction was the most responsible for the migration of phosphorus along the soil profile.