Summary and Implications
A 5-month study was conducted to evaluate the relationship between soil available phosphorus (P) and forage P concentrations in May, July, and September 2011. Four cool-season pastures were sampled at the Iowa State University McNay Research Farm near Chariton, Iowa. Forage samples were hand-clipped to ground level from a 0.25-m2 square and soil samples were collected to a depth of 5 inches within (400 ft or less) and outside (700 ft) of previously established congregation areas along one transect within each pasture. Forage P concentration increased with increasing soil available P content and decreased late in the grazing season. On average, the P concentrations of the forages exceeded the P requirement of lactating beef cows throughout the grazing season. A model of monthly forage P concentration predicted that the probability that P supplementation of cows would be necessary wouldn’t increase until October.
Iowa State University
Pille, Katrina and Russell, James R.
"Effects of Season and Soil Available Phosphorus Content on the Phosphorus Concentration of the Forage in Cool-Season Grass Pastures of Southeastern Iowa,"
Animal Industry Report:
AS 659, ASL R2777.
Available at: http://lib.dr.iastate.edu/ans_air/vol659/iss1/28