Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2003
Publication Date: 2/2/2004
Citation: WIENHOLD, B.J., MILLER, P.S. PHOSPHORUS FRACTIONATION IN MANURE FROM SWINE FED TRADITIONAL AND LOW-PHYTATE CORN DIETS. JOURNAL OF ENVIRONMENTAL QUALITY. 33:389-393. 2004. Interpretive Summary: Corn is the primary grain used in pig feed. Corn, like other plants, stores phoshorus in its seeds in a chemical form that pigs can not use efficiently. To overcome this producers have traditionally added phosphorus to feed. This results in added costs and high concentrations of phosphorus in swine manure. Low phytate corn stores phosphorus in a form that is more available to pigs, reducing the phosphorus concentration in manure. This study was conducted to compare the forms of phosphorus present in manure from pigs fed traditional corn diets to those in pigs fed low phytate corn diets. Manure from pigs fed low phytate corn diets had lower concentrations of total phosphorus and water soluble phosphorus. Water soluble phosphorus is the form of phosphorus that has the greatest potential for loss in runoff where it becomes a water pollutant. When expressed as a percentage of total phosphorus the forms of phosphorus were similar between the two manure types. When manure is used as a crop nutrient source the ratio of nitrogen and phosphorus contained in low phytate manure is more similar to that needed by a corn crop than is the ratio of nitrogen and phosphorus in tradational corn manure. When low phytate manure is applied to meet crop nitrogen needs phosphorus will accumulate less rapidly than for traditional manure and less land will be required to utilize the manure.
Technical Abstract: Traditional corn (Zea mays L.) (TC), the primary grain used in swine (Sus scrofa) diets, stores a majority of its P as phytate which is largely unavailable for digestion by nonruminant animals. Low bioavailability results in the need for supplemental P in feed, high P concentrations in manure, and potential environmental contamination when manure is land applied. Low phytate (LP) corn contains similar amounts of total P but stores a larger percentage of P as phosphate, which when fed to swine increases P bioavailability and reduces P content of manure. While differences in P content between manure from animals fed TC and LP corn diets have been documented, solubility and lability of manure P has not been compared. Manure P was characterized in manure from swine fed either LP or TC diets in 2000 and 2001. In both years, total P was lower (20 vs 32 g kg-1) and N:P ratio was higher (5.4 vs 4.5 in 2000 and 4.1 vs 2.9 in 2001) in LP manure than in TC manure. Manures were sequentially extracted with deionized water, 0.5 M NaHCO3, 0.1 M NaOH, and 1.0 M HCl. Extracts were analyzed for inorganic and total P. Most P in the extracts was in the inorganic form. Concentration of P in the water extractable fraction, the form available for runoff, was lower for LP manure than for TC manure. Percentage of total P present in each extract was similar for TC manure in 2000 and LP manure in 2000 and 2001 with the amount of P in each extract in the order H2O (57%), HCl (22%), NaHCO3 (11%), NaOH (8%), and residue (1%). In 2001, TC manure contained slightly higher amounts of P in H2O (65%), lower amounts in HCl (16%), and similar amounts in the remaining extracts when compared to other samples. Total P and distribution of P in extracts from the different manures indicates that while swine are able to utilize more of the P contained in LP corn feed the composition of P excreted in LP manure was similar to TC manure. Solubility, crop availability, and lability of P in LP manure should be similar to that of TC manure.