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Title:   Author  item
                                            Gollany, Heroitem
                                            SCHMITT, M. - UNIV. MINNESOTAitem
                                            BLOOM, P. - UNIV. MINNESOTAitem
                                            RANDALL, G. - UNIV. OF MINNESOTAitem
                                            CARTER, P. - PIONEER HI-BRED INTL
  Submitted to: Soil Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 6/24/2003
                                    Publication  Date: 9/1/2003
                                    Citation: GOLLANY, H.T., SCHMITT, M.A., BLOOM, P.R., RANDALL, G.W., CARTER, P.R. EXTRACTABLE PHOSPHORUS FOLLOWING SOIL AMENDMENT WITH MANURE FROM SWINE FED LOW-PHYTATE CORN. SOIL SCIENCE 168:606-616. 2003.Interpretive Summary: Specialization and intensification of agricultural systems has led to phosphorus (P) accumulation in excess of crop needs, with the consequent runoff polluting surface waters in many areas. Environmental P concerns and manure management are naturally linked in today's agriculture. Manure application rate recommendations have been based almost exclusively on nitrogen (N) management considerations, which can result in over-application of P and its accumulation in soil. An additional factor contributing to excess soil P is the application of monogastric animal (e.g. hog) manures.  This issue is of critical importance because hogs (unlike cattle) cannot digest phytate (the major form of P found in corn kernels).  As a result, much of the grain P passes through the animal and into the manure.  To assure healthy animal growth, supplemental inorganic P is included in the feed to meet nutritional needs.  In an effort to decrease the level of manure P, corn geneticists have selected a corn mutant that contains significantly less phytate with the same amount of total P, and breeders have backcrossed this trait into normal hybrids.  This customized corn, termed low-phytate (LP) corn, can be substituted for standard corn in feed and reduces the need for much of the supplemental inorganic P, and reduces the amount of P in manure.  

Our objectives were to determine soil P availability after hog manure application from different sources and compare the relative P availability of LP-manure to standard (S) manure.  A laboratory incubation study was conducted using a silt loam and a sandy loam soil, and three P sources (soluble fertilizer KH_2PO_4, S-manure, LP-manure) with a range (0-204 lb P acre^-1) of total P. Available P levels from manure of hogs fed low phytate corn and standard corn diets were compared with that obtained from a soluble P (KH_2PO_4) source.  Mineralization (conversion of organic forms to inorganic forms) of organic P was only detected at the highest LP-manure application rate for the silt loam soil.  Significant P mineralization was observed for the sandy loam soil.  Swine manure P availability was about 60% that of the KH_2PO_4 source for both manure sources.  The results of this study indicate that the total P concentration for the LP-manure was 42% lower than that for the S-manure. The important factor in the difference between manure sources is the 42% lower total P content for the LP-manure, not difference in availability
                                Technical Abstract: Manure application rate recommendations have been based almost exclusively on nitrogen (N) management considerations, which can result in over-application of phosphorus (P) and its accumulation in soil.  Low-phytate (LP) corn (Zea mays L.) was introduced into swine (Sus scrofa domesticus) feed to reduce the amount of P in manure.  The objectives of this study were to determine extractable P following swine manure application from different manure sources and compare the relative P availability of LP-manure to standard (S) manure.  A laboratory incubation study was conducted using a Waukegan silt loam and a Verndale sandy loam soil, and three P sources (KH2PO4, S-manure, LP-manure) with a range (0-229 mg P kg^-1) of total P (Pt).  Extractable P from manure of swine fed low-phytate corn and standard corn diets were compared with a soluble P (KH_2PO_4) source.  The effect of P application rate on extractable soil P was linear (r^2 > 0.97).  Small but significant P mineralization was observed for the Verndale sandy loam soil.  Mineralization of organic P was only detected at the highest LP-manure application rate for the Waukegan silt loam soil. Relative to KH2PO4, the LP-manure and S-manure had P availability indices (PAI) of 0.55 and 0.61, respectively. Swine manure P availability was about 60% that of the KH_2PO_4 source for both manure sources.  The total P concentration for the LP-manure was 42% lower than that for the S-manure. The important factor in the difference between manure sources is the 42% lower total P content for the LP-manure, not difference in availability.  Further evaluation of available P from LP-manure is needed under field conditions.


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