Beyond pH: Metabolic Factors Affecting Pork Quality

Controlling nutrient losses from animal manures when they are landapplied is a critical factor in nutrient management, promoting environmental health and maintaining the sustainability of animal agriculture. Phosphorus is of particular concern due to its implication in eutrophication of surface waters and declines in water quality. We conducted a laboratory experiment to test the effect of several chemical amendments on reducing P solubility of animal manure. Freshly excreted swine or dairy manure samples were treated with aluminum sulfate (alum) or coal combustion byproducts: fluidized bed combustion flyash (FBC), flue gas desulfurization product (FGD), or anthracite refuse flyash (ANT). After incubation at ambient temperature for 3 d, subsamples were dried and ground. Samples were extracted with shaking for 1 hr in deionized water and the pH and inorganic and total P concentrations measured. Selected samples were extracted using a sequential procedure developed in our laboratory to identify the changes in soluble P forms as a function of amendment type and rate. Compared to untreated controls, alum, FBC and FGD substantially reduced water soluble inorganic P in the 1 hr extract in fresh swine manure (by 80, 60 and 77%, at 250, 400 and 250 g amendment per kg DM manure, respectively). The 1 hr water extractable inorganic and total P in dairy manure were reduced by an average of 65 (alum at the 50 g rate) and 50% (FBC at the 400 g rate). The ANT amendment was ineffective in reducing water soluble P in swine manure, and both ANT and FGD ineffective in dairy manure. In the sequential, repeated extraction trial, addition of the amendments alum, FBC or FGD to swine manure reduced the total water soluble inorganic P concentration and increased the concentrations of bicarbonate, hydroxide and acid-soluble P by 11-21% compared to the control, demonstrating effectiveness in shifting inorganic P from the most vulnerable, water-soluble fraction to less soluble forms. The alum and FBC amendments had a similar effect on the dairy manure samples. Additional trials are planned to examine the amendments for other manure types and to refine effective rates of addition to reduce soluble P.