Using Zero-Tension Lysimeters to Determine the Effect of Grazing On Nutrient Cycling.

Management intensive grazing (MIG) has been implemented as a low input alternative to traditional grazing or haying practices.  MIG involves high stocking rates of livestock rotated through several small pastures, or paddocks, typically grazing the area for a short period of time. Deferred, or stockpiled grazing, is used to extend the grazing season.  Deferred pastures accumulate forage during the late summer and early fall and are grazed in the late fall and early winter.  This practice reduces the amount of baled hay needed for winter feeding; thereby reducing winter feed costs.  However, it also adds nutrients to the system at a point when the forage crop can not readily use them.  

This study examined nitrogen and phosphorus leaching in tall fescue (Festuca arundinacea) plots under three different grazing techniques: no grazing (NG); deferred grazing (DG); and standard management intensive grazing (MIG).  The NG plots were mechanically harvested.  The DG plots utilized standard MIG until the last grazing event when it was allowed to stockpile until November, when it was the only treatment grazed.  Plots were grazed for 24 hours, approximately every 6 weeks.

Zero-tension lysimeters, 38.1 cm in diameter and 1.12 meters in depth, were built using a hollow-core drill to obtain undisturbed soil cores.  PEX tubing running underground from the collection reservoir at the base of the lysimeter to a vacuum pump outside of the plot area was utilized for leachate collection.  Leachate was collected bi-weekly and analyzed for nitrate-nitrite and inorganic dissolved phosphorus.  Soil cores were take at the beginning and end of each grazing season and analyzed for nitrogen and phosphorus.  Results from a three-year study will be presented.