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United States Department of Agriculture

Agricultural Research Service

Title: Extractable Phosphorus Following Soil Amendment with Manure from Swine Fed Low-Phytate Corn

Authors
item Gollany, Hero
item Schmitt, M. - UNIV. MINNESOTA
item Bloom, P. - UNIV. MINNESOTA
item Randall, G. - UNIV. OF MINNESOTA
item Carter, P. - PIONEER HI-BRED INTL

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 24, 2003
Publication Date: September 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.

Last Modified: 10/21/2014
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