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United States Department of Agriculture

Agricultural Research Service

Research Project: UNDERSTANDING PHOSPHORUS CHEMISTRY IN MANURE AND SOIL AND THEIR INTERACTIONS TO TREAT AND CONTROL PHOSPHORUS MOVEMENT IN THE ENVIRONMENT Title: Time Dependent Bioactive Phosphorus Extractability in Calcium and Iron-Treated Soils

Authors
item Dao, Thanh
item Codling, Eton
item Schwartz, Robert

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 6, 2005
Publication Date: November 6, 2005
Citation: Dao, T.H., Codling, E.E., Schwartz, R.C. 2005. Time dependent bioactive phosphorus extractability in calcium- and iron-treated soils. [abstract]Agronomy Abstracts. CD-ROM.

Technical Abstract: Practices to reduce phosphorus (P) source bioavailability are gaining acceptance in the management of excessive P in manure and P-enriched soils although the environmental behavior of the immobilized P is largely unknown. Water-extractable dissolved and complexed P forms (i.e. bioactive P) and Mehlich-III P were determined during a 16-week soil incubation to elucidate mechanisms of stabilization and P extractability as affected by Ca2+ and Fe3+-amendments in an Aridic Haploxeroll and an Oxyaquic Hapludult. The Fe3+ additive reduced WEP by over 90% when applied at a rate of 0.18 mole kg-1. However, potentially bioactive P can increase with time and that the use of Mehlich-III P may not appropriately reflect this potential to contribute P to the impairment of surface waters. Mehlich-III P levels in Fe3+-treated soils were reduced, after that remained unchanged up to 16 weeks. The phytase-hydrolyzable P (PHP) fractionation method, however, revealed that the additives' effect was transitory; increasing previously insoluble inorganic EDTA-extractable P (EEP) was extractable and organic PHP was exchangeable and susceptible to enzymatic dephosphorylation over time to revert back to initial levels. Calcium carbonate amended at a liming rate to raise soil pH to near neutrality negated the environmental benefit of applying iron-rich P-immobilizing additives to both soils. The temporary suppression might resolve a short-term elevated soluble P condition, however, was not effective in mitigating the long-term risks of bioactive P losses from P-enriched soils.

Last Modified: 10/25/2014