Phosphorus Availability of Broiler Breeder Manure Pellets for Corn across Soil Phosphorus Gradient.

Broiler breeder diet modifications to reduce phosphorus (P) excretion were previously evaluated for manure P characteristics and P transformation once soil-applied.  Few studies have evaluated plant P availability of such manures.  Pelletized manure from standard non-phytate P (NPP) and reduced NPP diets were evaluated for corn P availability at three long-term P fertility sites in the North Carolina piedmont (Salisbury) and the coastal plain (Lewiston, Plymouth).  Pelletized manures were applied at 39 kg P ha^-1, which is a standard recommendation for a single corn crop in North Carolina.  Pelletized manures from standard NPP and reduced NPP diets yielded 21.7 and 15.7 g P kg dry manure^-1, respectively.  These P-based treatments were applied across three soil P levels in Salisbury and Lewiston and four soil P levels in Plymouth.  Two additional treatments, triple superphosphate (TSP) and an untreated control, were implemented across soil P levels in Plymouth to determine fertilizer equivalency and endogenous soil P supply.  Early corn biomass accumulation of P was marginally higher in pelletized manures.  Harvest P removal was no different among P sources, which is most likely due the high orthophosphate content of the manures (94 to 98% based on ³¹P Nuclear Magnetic Resonance), and therefore, manures were equivalent to TSP in the first growing season.  Grain P removal ranged from 20.8 to 34.7 kg P ha^-1 in the low P to high P soils, respectively, where these soils supplied 6.7 to 27.9 kg P ha^-1 yielding 36 to 17% applied-P use efficiency.  Residual P supply from these applications will be evaluated in the following growing season.  Future research will target poultry manures of different orthophosphate proportions to determine plant P availability as soil-applied at a range of rates across low soil P sites.