Sunday, November 12, 2006 - 3:30 PM

Phosphorus Characterization of Manure and Manured Soils after Feeding Phytase and Distillers Dry Grains Solubles to Swine.

Crystal Freeman1, Neil Hansen2, James Ippolito1, and Gerald Shurson3. (1) Colorado State Univ, Dept of Soil and Crop Sciences, C127 Plant Sciences Building, Fort Collins, CO 80523-1170, (2) Colorado State Univ., Dept of Soil & Crop Science (1170), Ft. Collins, CO 80523-1170, (3) Univ. of Minnesota, Dept of Animal Science, Saint Paul, MN 55108-6118

Some livestock farmers have claimed that diets containing the ethanol byproduct distillers dried grains with solubles (DDGS) result in lower P concentrations in manure than similar formulations without DDGS.  We studied four manures from diets which included a corn and soybean diet, and a distillers dried grains with solubles (DDGS) diet, both with and without phytase additions. Addition of phytase reduced P excretion in manure, while addition of DDGS did not.  Both phytase and DDGS in the diet reduced the concentration of soluble P in the manure.  In a lab benchtop study, the four manures were mixed in to three different Minnesota soils, including a glacial till, glacial outwash, and a lacustrine soil, in 150 mL plastic beakers with screw top lids.  Experimental setup was a completely randomized design with four replicates.  Mixtures were kept at 70% of field capacity by weekly water additions, and incubated for up to 120 days.  Soil samples were collected at 30 days, 90 days, and 120 days after starting the incubation and were characterized for water soluble P and Mehlich-III extractable P concentrations.  The water soluble P extraction contained 45%, 57%, and 45% of manure-applied P after 30, 90, and 120 days of incubation, respectively.  Diets with phytase or diets with DDGS showed modest reductions in water extractable P compared to the control diet.  The Mehlich-III P extraction contained 72%, 85%, and 85% of manure applied P after 30, 90, and 120 days of incubation, respectively and there was no diet effect. This data suggests that feeding either phytase or DDGS may have the potential to reduce P in runoff without reducing plant available P in manure amended soils.  There is no added benefit from the combination of phytase and DDGS.