Evaluation of Quick Tests for Dissolved Phosphorus Determination in Dairy Manures.
(A05-reeves,iii921387-poster)
Authors:
J.B. Reeves, III* - USDA A. Lugio-Ospina - USDA T.H. Dao - USDA
J.A.S. Van Kessel - USDA
Abstract:
The objective was to evaluate the suitability of a hand-held reflectometer, hydrometers, electrical conductivity (EC), and manure total solids (TS) concentrations for determining dissolved and/or total P (DP and TP, respectively) in dairy manure suspensions. Dairy manure samples (n=107) were collected from farms across CT, MD, NY, PA, and VA. The manure samples were highly variable in total solid concentrations, ranging from 11 to 213 g L-1 and in suspensions’ pH (6.3 to 9.2) and electrical conductivity (6.2 to 53.3 dS m-1). On a gravimetric basis, the RQFlex reflectometer yielded lower DP estimates that were related to molybdate-reactive phosphorus (MRP) concentrations as follows:
RQFlex-DP = 0.471 * MRPs + 1102 (r2 = 0.293). An improved correlation was found for 102 of the 107 samples (RQFlex-DP = 0.947 * MRPs + 509; r2 = 0.637) upon excluding samples of highest MRP. Low manure suspension pH values were associated with high DP, especially for the MRP
method. The prediction of manure DP from RQFlex results, on a volumetric basis, required the inclusion of pH and squared-pH in the predictive equation. Manure TS concentrations or hydrometer readings were not related to either RQFlex-DP or MRP concentrations.In conclusion, experimental results indicate that only the RQFlex method is a viable option for on-site measurements of dissolved P concentrations in dairy farm manure, and even then only a rough estimate is possible.
Speaker Information: James Reeves, III, USDA, AMBL, ANRI Bldg 306, Rm 101 BARC East, Beltsville, MD 20705; Phone: 301-504-8294; E-mail: [email protected]
Session Information: Wednesday, November 5, 2003, 4:00 PM-6:00 PM Presentation Start: 4:00 PM (Poster Board Number: 232)
Keywords: Phosphorus; Dissolved; Dairy; Manure