Last summer, intern Garrett Hatfield conducted a defoliation experiment that looked at the impact of grazing height and frequency on soil and crown temperature of a tall fescue stand.  The results of Garrett’s experiment were dramatic.

Garrett clipped the plots to a height of either 1” or 4.5” every week from mid-May to September or monthly to 4.5” .  The weekly clipping treatments represent what you would expect in a continuously grazed pasture, with the 1” defoliation height representing a high stocking rate and the 4.5 inch defoliation height representing a more moderate stocking rate.  The monthly defoliation treatment represented a rotational grazed pasture, where stands are grazed and then rested for 30 days.

The primary objective of this study was to document the impact of the defoliation treatments on the crown and soil temperatures in tall fescue pastures.  Increased crown and soil temperatures during the summer months likely stresses cool-season grasses, negatively impacting stand persistence and productivity.  Temperatures were documented by installing dataloggers that automatically measured and recorded temperature every 15 minutes.

On hot days, the temperature at the base of the tall fescue plants was more than 10 degrees higher when the stand was clipped to 1” vs. 4.5”.  Even when averaged over the entire summer, plots that were clipped close had soil temperature about 10 degrees higher.

One of the interesting observations was that after only 4 to 5 weeks of 1” clipping, we saw the composition of the grass stand change from tall fescue to crabgrass.  Crabgrass is a summer annual grass that fills in cool-season grass stands as they thin.  Now crabgrass is a high quality forage, but it’s going to die out after frost and leave patches of bare soil over winter for weeds to grow. Another interesting observation was made this spring.  Plots that had been clipped to 1” every week the previous summer, were thinner, weedier and contained more common white clover.  Common white clover can survive under close and frequent defoliation, but its yield potential and drought tolerance is low.

Take Home: From a practical standpoint, the results of this study indicate the importance of 1) not grazing pastures closer than about 4” and 2) resting pastures between grazing events, especially during the summer months.  ~ excerpt from Chris Teutsch’s column in Cow Country News. See full article here.