Effect of Feeding Wet Distillers Grains On Phosphorus in Feedlot Manure and Surface Runoff.

With the rapid expansion of grain-based ethanol production, distillers grains (DGS) have become a viable feeding option to the animal industry. Many studies have indicated that phosphorus (P) concentrations in manure increase from cattle fed DGS.   It has been estimated that feeding 20 or 40% DGS increased P in the manure from the feedlot 60 and 120%, respectively.  Total P concentrations are usually determined in manure fed various diets.  However, water extractable P (WEP) concentrations have not been measured from diets containing DGS.  Water extractable P, also known as soluble P, concentrations in manure have been shown to be highly correlated to P concentrations in runoff.  The objectives of this study are to determine the effect of feeding wet distillers grains plus soluble (WDGS) on 1) total P and WEP concentrations in manure; and 2) P concentrations in runoff water after land application to no-till and conventionally tilled wheat.  This study was conducted at the USDA-ARS/Texas AgriLife Research experimental feedlot at Bushland, TX.  Cattle were fed diets of 1) flaked corn (control 1); 2) cracked corn (control 2); and WDGS at 3) 15%; 4) 30%; 5) 45%; and 6) 60% with flaked corn.  Steers were housed in open lot pens for the duration of the 180 d feeding trial.  At the end of the study, manure was scraped and weighed from each pen.  Manure was collected from each of the six diets and analyzed for total P and WEP.  Manure was applied to small runoff plots (1.5 x 2 m) at rates equivalent to 22.4 Mg ha^-1.  Manure was surface applied to all runoff plots and was incorporated on conventionally tilled plots prior to planting.  Rainfall simulations were conducted two weeks after manure application.  Results will be discussed, as data were being collected and analyzed at the time of submission.