Temperate Perennial Grass Response to Defoliation Height and Interval.

The frequency and extent to which temperate perennial grasses are defoliated influences their productivity and persistence.  Field-grown tillers of meadow fescue (Festuca pratensis Huds.), orchardgrass (Dactylis glomerata L.), common quackgrass [Elymus repens (L.) Gould], and reed canarygrass (Phalaris arundinacea L.) were planted in 4- by 21-cm cone-shaped cells containing 5 g slow-release fertilizer and a 1:2:1 mixture by volume of commercial topsoil, sand, and organic media.  Day-night greenhouse temperatures from November to March averaged 22.6 and 17.6 C.  Ambient light was supplemented with high-pressure sodium vapor lighting (1600 μmole m^-2 s^-1 for a 12-h photoperiod).  Tillers were grown 45 d before being clipped to a 5- or 10-cm height every 7, 14, 21, 28, and 35 d.  Response to defoliation was measured 7, 14, 21, and 28 d after the last clipping.  Root dry wt. of all grasses was greater at the 10- vs. 5-cm clipping height, and increased as defoliation interval increased for both heights.  Results for no. of tillers were similar to root dry wt., except reed canarygrass produced equal number of tillers at 5- and 10-cm height at each defoliation interval.  Dry wt. tiller^-1 of all grasses was also greater at 10- vs. 5-cm height, but only orchardgrass exhibited increasing dry wt. tiller^-1 as interval increased.  All grasses displayed sensitivity to defoliation height, but orchardgrass benefited most from increasing defoliation interval.