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Does feeding low phytate corn change the availability of manure phosphorus when it is land applied to crop fields? It has been well-documented that feeding low-phytate corn to pigs can significantly reduce the amount of phosphorus (P) excreted in their manure. What has not been previously explored is whether the P in that manure is equally available to plants as in manure from pigs fed conventional corn. Previous laboratory analyses have suggested that the availability is likely similar, but it has yet to be proven under field conditions.
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Four Nebraska researchers worked with two types of corn from the same cultivar. One exhibits the low-phytate trait and one exhibits conventional phosphorus traits. Each type of corn was incorporated into rations and fed to separate groups of pigs and the manure from each group was collected and stored separately.
Research plots received manure from pigs fed typical corn, manure from pigs fed low-phytate corn (LPC), inorganic fertilizer, or no nutrient addition (control). The research was repeated over a three-year period at two different locations. Inorganic fertilizer was applied at recommended rates based on previous site yields and was not adjusted for residual soil inorganic N or extractable P. Manure applications on the plots were made at rates intended to meet crop nitrogen needs. Due to the different P content of the manure, total P application to plots receiving manure from pigs fed LPC was less than to plots receiving manure from pigs fed conventional corn.
What Does This Mean?
In this study, manure from swine fed low-phytate corn (LPC) had a N:P ratio (4.5:1) closer to corn crop needs (6:1) compared to manure from animals fed conventional corn (3.3:1). Even though less total P was applied to plots receiving manure from pigs fed LPC, it was still highly extractable (100%) and sufficient to meet crop needs.
Feeding LPC to pigs appears to have several management benefits for producers following nutrient management plans. When manure from pigs fed LPC is land-applied to meet crop nitrogen needs, less excess P will be applied (compared to manure from pigs fed conventional corn) and accumulate over time. When the same manure is applied to meet crop P needs, less inorganic N fertilizer will need to be applied (when compared to manure from pigs fed conventional corn) to meet crop needs.
For More Information
This research was published in the Soil Science Society of America Journal. Anyone can access the abstract for free. Members of the Soil Science Society of America can access the full-text for free, while non-members can pay a fee to view the full text.
The authors of the study are J.S. Paschold and B.J. Wienhold (Brian.Wienhold@ars.usda.gov), USDA ARS Agroecosystem Management Research Unit and R.B. Ferguson and D.L. McCallister, University of Nebraska-Lincoln.
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