PHOSPHORUS MANAGEMENT Ligands and Phytase Hydrolysis of Organic Phosphorus in Soils Amended with Dairy Manure

tion of IP6 and other IPs in dairy manure are attributed to the protective effect of IP6 complexation with polyvaInformation about orthophosphate and organic phosphorus (P) lent cations that reduces dephosphorylation. As a result, desorption in soil amended with animal manure is needed because a build-up of P following repeated manure applications poses risks of substantial amounts of dietary IP6-P of feed grains are offsite dissolved P discharges. An enzymatic hydrolysis and soil P excreted, contributing to water pollution rather than desorption study was conducted to develop a novel ligand-based phyanimal growth and development. tase-hydrolyzable P (PHP) method and quantify water-extractable In soils amended with animal manure, IP6 and other uncomplexed and complexed P forms (i.e., bioactive P) in Unicorn organic P are added to the soil P pool, in addition to and Christiana soils (Typic Hapludults). Extractability of inorganic inorganic PO4–P. The need for detailed organic P charP with ligands alone (LEP) increased from 2 and 22 mg kg 1 (0.3 and acterization studies is critical as orthophosphate mono3.1 0.16% total P) up to sevenfold with increasing ligand (LIGND) and diesters have been observed to move through soils, concentrations in the order of CDTA EDTA DTPA oxalate. posing risks of water quality degradation via soil subsurThe LIGNDs nullified the benefits of using an anion sink in soil P face transport (Wild and Oke, 1966; Gerritse and Ekdesorption measurements. Soil organic P was hydrolyzed in situ by Aspergillus ficuum (Reichardt) Henn. phytase EC 3.1.3.8, corroboratsteen, 1978; Chardon et al., 1997). myo-Inositol hexakis ing the presence of myo-inositol phosphomonoesters including IP6. dihydrogenphosphate and lower phosphomonoesters of Adding CDTA and EDTA increased phytases’ efficacy and that of inositol are the most abundant identifiable organic P the PHP assay for measuring previously inaccessible complexed orcompounds, and may make up to 50% of total soil organic P; soil PHP increased from 2.3 and 6.4% to peak at 32.0 0.7 ganic P (Cosgrove, 1962; Wild and Oke, 1966). The and up to 40.8 0.2% of total P in Unicorn and Christiana soils, phosphomonesters have been identified by 31P nuclear respectively. In long-term manure-amended Christiana silt loam under magnetic resonance (NMR) spectroscopy, using alkaorchardgrass–red clover stands, the LIGND-PHP method showed line extractants such as 0.5 M NaOH or 0.25 M NaOH– that repeated manure applications resulted in soil storage of unextract0.05 M Na2EDTA (Newman and Tate, 1980; Cade-Menun able complexed PHP and a buildup of inorganic LEP. Accumulation et al., 2002; Koopmans et al., 2003). Although such of LEP increases risks of mobilization of bioactive P in the top 10 cm of these soils. methods yield structural identity and chemical classes information, current NMR techniques measure total orthophosphate monoesters and diesters in the soil extracts. Alterations in chemical form may occur because I areas of intensive animal agriculture, soils treated of the high alkalinity of the extraction medium, i.e., with large amounts of manure accumulate and show hydrolysis of orthophosphate diesters (Leinweber et elevated inorganic and organic P contents (Zhang et al., al., 1997). 2002). Animal manures are major sources of organic P Extracellular enzymes have been used in the charac(Peperzak et al., 1959; Gerritse and Eksteen, 1978; Dao, terization of organic P because substrate specificity and 2003a). The organic P fraction is composed principally variety of phosphatases provide an analytical approach of myo-inositol phosphomonoesters (IP), and in smaller to determining organic P forms in animal manure (He proportion, phospholipids and orthophosphate diesters. and Honeycutt, 2001; Dao, 2003a), soil extracts (Hino, myo-Inositol hexakis dihydrogenphosphate (IP6) is ex1989; Shand and Smith, 1997), and leachates (Toor et creted in animal manure as swine and poultry lack the al., 2003). Current enzymatic methods have been hamphytase enzymes to break down IP6 (Harper et al., 1997). pered by a relatively low recovery of soil P (Shand and Manure from ruminant livestock, thought able to utilize Smith, 1997; Hayes et al., 2000); for example, Hayes et IP6-P because of microbial hydrolytic activity in the al. (2000) reported 2% of soil total P (6.2 mg kg 1) rumen and intestinal mucosa, also contains a large phywas desorbed and hydrolyzed in a 50-mM citric acid tase-hydrolyzable P pool (Dao, 2003a; Dao et al., perextract and much less (0.3 mg kg 1) in a water extract. sonal communication, 2004). The persistence and excreSoil P recovery depended upon the solvent strength as well as the form of the extracted organic P because most USDA-ARS, AMBL, BARC-East, Beltsville, MD 20705-2350. The mention of trade or manufacturer names is made for information only Abbreviations: CDTA, 1,2-cyclohexane diamino-tetraacetate; DTPA, and does not imply an endorsement, recommendation, or exclusion diethylenetriamine-N, N, N , N′′, N′′-pentaacetate; EDTA, ethyleneby the USDA-ARS. Received 15 Dec. 2003. *Corresponding author diamine-N, N, N , N -tetraacetate; LIGND, other, non-IP6 organic ([email protected]). ligand; IP, myo-inositol phosphate monoesters; IP6, myo-inositol 1, 2, 3, 5/4, 6-hexakis dihydrogenphosphate; LEP, inorganic ligandPublished in Agron. J. 96:1188–1195 (2004).  American Society of Agronomy extractable P; PHP, phytase-hydrolyzable P; WEP, water-extractable P; ZVMA, zerovalent metal alloy. 677 S. Segoe Rd., Madison, WI 53711 USA