Effect of phytase and vitamin D metabolite (25OH-D₃) in turkey diets on phosphorus solubility in manure-amended soils

It has become common practice to use feed additives (such as phytase) to increase the digestibility of phytate-P to monogastric animals, decreasing the need for P supplements to diets and decreasing the total P content in manures. In this study, the effect of incorporating phytase/and 25-hydroxycholecalciferol (25OH-D₃) in turkey diets on the solubility of P in turkey manures (TMs) and TM-amended soils was investigated. Turkey manures were collected from turkeys fed (i) a normal diet, and three diets containing reduced nonphytate P (nPP) called (ii) P deficient, (iii) phytase, and (iv) phytase+25OH-D3. The TMs were added to five soils at the same total P rate (150 kg P ha^-1) and incubated for 42 days. The dried TMs were analyzed for water soluble-P (WS-P) and total P, whereas the incubated soils were analyzed for pH, organic matter (OM), Mehlich-3 P, Al, and Fe (M3-P, M3-Al and M3-Fe), water soluble-molyb-date reactive P (WS-MRP), and organic-P (WS-OP). The normal diet produced TMs that had six times higher WS-P and more than 40% greater total P than any of the reduced nPP diets. Adding phytase to the reduced nPP diets did not increase the percentage of total P that was water soluble. As a result of its greater P content, TM from the normal diet increased soil WS-MRP, but not M3-P or WS-OP, to a greater extent than the reduced nPP diets. All TMs increased WS-MRP relative to the unamended soil, and these increases were inversely related to the M3 [Al+Fe] content of each soil. Converting from a normal turkey diet to one that contains reduced nPP and phytase/and 25OH-D₃ shows potential for reducing total and soluble P in manures and soluble P in manure-amended soils. As reduced nPP, phytase/and 25OH-D₃ in diets lead to reduced TM total P, long-term applications of these reduced P TMs using nitrogen-based management would be expected to reduce total P and Mehlich-3 P in soils, compared with TMs from normal diets.