Effect of Grazing On Compaction and Nitrogen Cycling.

Grazing can lead to compacted soils and result in restricted water infiltration, root growth, and break down of soil structure.  This will likely increase the potential for anaerobic processes such as denitrification to occur.  Although denitrification is not harmful environmentally, it can result in substantial nitrogen loss.  In addition, compacted soil may increase nutrient losses via ammonia volatilization, and water runoff.  Deferred, or stockpiled grazing, is used to extend the grazing season and reduce winter feeding costs.  Deferred pastures accumulate forage during the late summer and early fall and are grazed in the late fall and early winter.  This study examined the effects of grazing on soil compaction, nitrate leaching, and ammonia volatilization.   Management intensive grazing (MIG), deferred grazing (DG), and mechanical harvest (NG) were compared.  Grazing events occurred approximately every 6 weeks for 24 hours.  Leachate was collected bi-weekly from zero-tension lysimeters at a depth of 1 meter and analyzed for nitrate-nitrogen.  Ammonia volatilizaton was measured using dynamic chambers.  Tension infiltrometer, bulk density, and soil samples were collected prior to grazing, and after the normal grazing season ended.  Soil samples were analyzed for nitrate-nitrogen.  Results will be presented.