With Increasing Availability of Distillers Grains Will Phosphorus Be a Problem for Iowa Livestock Producers?

Retention and excretion of phosphorus were calculated using NRC equations for metabolism of phosphorus in beef cattle fed 0, 20 or 40% distillers grains (DGS). These estimates of phosphorus excretion were similar to quantities of phosphorus excretion measured in experiments with cattle. The predictions of phosphorus retention and excretion were used to estimate phosphorus balance of a 1000-head feedlot in which the cattle were fed 0, 20 or 40% DGS. Feeding 20 or 40% DGS increased phosphorus in the manure from the feedlot 60 and 120%, respectively. However there was not adequate phosphorus in the manure to replace soil phosphorus removed in the crops to produce the feeds for the cattle. The areas of land needed for manure disposal were calculated to be 470, 554 & 608; 756, 890 & 977 and 1,052, 1239 & 1,359 acres for crop rotations of continuous corn, corn-corn-soybeans and corn-soybeans when the cattle were fed 0, 20 or 40% DGS. These results indicate that feeding DGS does not innately cause an environmental problem, but will require each feedlot to develop manure management plans. Use of farm phosphorus balance seems to be a plausible approach to develop reliable manure management plans for feedlots feeding DGS