MANAGING PHOSPHORUS-ENRICHED SOILS: EFFECTS OF IRON AMENDMENT ON TEMPORAL DYNAMICS OF BIOACTIVE PHOSPHORUS POOLS

Authors: Dao, Thanh; Codling, Eton; Schwartz, Robert

Submitted to: World Congress of Soil Science
Publication Type: Abstract Only
Publication Acceptance Date: 7/9/2006
Publication Date: 7/15/2006
Citation: Dao, T.H., Codling, E.E., Schwartz, R.C. 2006. Managing phosphorus-enriched soils: effects of iron amendment on temporal dynamics of bioactive phosphorus pools [abstract]. World Congress of Soil Science, July 9-15, 2006, Philadelphia, PA. No. 154-11 [CD-ROM].

Interpretive Summary: .

Technical Abstract: An enzyme hydrolysis and soil phosphorus desorption study was conducted to determine whether the rate of buildup of manure inorganic and organic forms of phosphorus differs between soils and cropping systems. Water-extractable labile forms and complexed forms that are potentially bioactive were measured in Unicorn and Christiana soils (Typic Hapludults) that have received long term additions of cattle (Bos taurus) manure. The in situ phytase-hydrolyzable phosphorus (PHP) assay showed that repeated land applications resulted in soil storage of unextractable complexed organic PHP and a buildup of inorganic ligand-exchangeable phosphorus (EEP). The accumulation of EEP increases risks of potential mobilization of bioactive inorganic phosphorus whereas biological hydrolysis of organic PHP also potentially contributes more soluble phosphorus to the near-surface zone of these soils. Manure additives and soil amendments commonly used to reduce phosphorus source solubility include phosphorus-immobilizing agents such as lime and municipal by-products containing metal sesquioxides. These practices are gaining acceptance although the speciation and environmental behavior of the immobilized phosphorus is yet largely unknown. The phytase-hydrolysable phosphorus fractionation method revealed that the additives’ effect was transitory; increasing previously insoluble inorganic EEP was extractable and more organic PHP was exchangeable and susceptible to enzymatic dephosphorylation over time to revert back to initial soil levels about four weeks after the iron addition. The temporary suppression might resolve a short-term elevated soluble phosphorus condition, however, was not effective in mitigating the long-term risks of bioactive phosphorus losses from phosphorus-enriched soils. Therefore, we must depend upon a biological tool to detect internal biochemical changes in the susceptibility of soil phosphorus inorganic and organic pools over time as the traditional soil test method was insensitive to these internal pool transfer and changing stability of the water-insoluble phosphorus species.