Fertilization of Heavily and Moderately Grazed Mixed-Grass Prairie With Slow-Release Phosphorus and Urea


Two sites of 45 meters by 60 meters were chosen, one in a heavily grazed pasture and the other in a moderately grazed pasture (Figure 2). Within each site, four repetitions of 21 meters by 15 meters were laid out and seven different treatments were placed within each repetition. Each treatment is three meters by 15 meters. A five-meter alley way separates each repetition with a 6.5-meter buffer around the outside. Fertilizer rates of 24 and 48 lbs of P per acre were applied on May 1 and June 20. Applications of 33 and 66 lb/acre of N were also made on June 20. The fertilizers used are slow-release Polyon fertilizers purchased from Pursell Technologies Inc.

Over the course of the summer, four clippings were taken of five plant species to map the uptake of phosphorus. The five species clipped were western wheatgrass (Agropyron smithii), green needlegrass (Stipa viridula), Kentucky bluegrass (Poa pratensis), smooth brome (Bromus inermis), and buckbrush (Symphoricarpos occidentalis). These samples were dried at 150 degrees F then ground through a 1mm screen in a Wiley Mill and are now being tested for phosphorus content in the NDSU Animal and Range Sciences Nutrition Lab. Also a separate clipping was performed to establish production on each of the treatments. This was done by clipping three samples on each treatment separated into warm season grasses, cool season grasses, forbs, shrubs, litter and standing dead material. These samples were dried at 150 degrees Fahrenheit for 48 hours then weighed. An average of the three samples per treatment was calculated followed by an average of each treatment on all four repetitions of each grazing intensity.

The results of the 2000 growing season will be presented at the Central Grasslands Research and Extension Center's winter meeting.

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