Effect of Wet Distillers Grain Diets On Phosphorus Runoff From Feedlots and Land Application Sites.

With the rapid expansion of grain-based ethanol production, distillers grains (DGS) have become a viable feeding option to the animal industry. However, many studies have indicated that phosphorus (P) concentrations in manure increase as a result of feeding DGS.   Two studies were conducted to evaluate the effect of feeding wet distillers grains plus solubles (WDGS) on P runoff from feedlots and cropland.  The objective of the first study was to determine the effect of feeding WDGS on 1) P concentrations in runoff water after land application to no-till and conventionally tilled wheat.  The objective of the second study was to determine the effect of diet and feedlot surface on P runoff. All feeding trials were conducted at the USDA-ARS/Texas AgriLife Research experimental feedlot at Bushland, TX.  In study one, cattle were fed diets of 1) steam flaked corn (control 1); 2) dry rolled corn (control 2); and WDGS at 3) 15%; 4) 30%; 5) 45%; and 6) 60% with steam flaked corn.  Phosphorus losses in runoff water were highest from diets containing 45% and 60% WDGS.  Losses of P were also typically higher from no-till plots compared to conventionally tilled plots. In study two, cattle were fed control and WDGS diets within pens containing soil or fly ash surfaces.  Rainfall simulations were conducted at the conclusion of the feeding trial.  Results will be discussed, as data were being collected and analyzed at the time of submission.