Wednesday, November 15, 2006

Factors Affecting Water-soluble Phosphorus in Animal Waste.

Yebin Zhao1, Kang Xia2, Armando S. Tasistro1, Miguel Cabrera3, Dorcas Franklin4, and David Kissel5. (1) University of Georgia, 3111 Plant Sciences Building, 3111 Plant Sciences Building, Athens, GA 30602, United States of America, (2) Mississippi State Chemical Lab., P.O. Box CR, Mississippi State, MS 39762, (3) University of Geogia, Dept of Crop and Soil Sciences, 3111 Miller Plant Sciences Building, Athens, GA 30602, (4) USDA-ARS, 1420 Experiment Station Road, Watkinsville, GA 30677, United States of America, (5) Dept. of Crop & Soil Sciences, University Of Georgia, University Of Georgia, Athens, GA 30602, United States of America

Water-soluble phosphorus (WSP) in animal manures has received recent attention because phosphorus (P) extraction by water may closely simulate extraction by rainfall and runoff water in the field. When manures are extracted with water, however, the extraction pH is equal to that of the manure because water is not buffered.  In contrast, when manures are applied to soil, their pH decreases rapidly to that of the soil, which may lead to an increase in soluble P.  Consequently, extraction of WSP with a solution buffered to the pH of the soil may more closely resemble the amount of P that may be extracted by rainfall and runoff water.  Water-soluble P is commonly defined as the fraction that passes through a 0.45-micron filter and consists mainly of dissolved reactive P (DRP), most of which is inorganic P.  Another fraction of interest in WSP is the soluble bioavailable phosphorus (SBAP), which can be measured by the iron-oxide sink method. This method has been used to measure bioavailable P in soil and runoff water, but no comprehensive study has been conducted with animal manures.  We studied the effects of three shaking times (1, 4, and 24 h), three manure: water extraction ratios (1:10, 1:100 and 1:200), and two pH’s (unmodified animal manure pH, and buffered solution at pH 6.0) on WSP, DRP, and SBAP extracted from broiler litter, layer manure, and dairy slurry samples.  Maximum amounts of WSP and DRP were extracted from all manures with a buffered solution at pH 6, a 1:200 extraction ratio, and 4 h of extraction time.  Maximum amounts of SBAP were obtained with the same method, but extending the extraction to 24 h.  Amounts of WSP, DRP, and SBAP extracted with this method should be compared to those measured in runoff to determine the validity of the method.