Regrowth of crested wheatgrass (Agropyron cristatum [L.] Gaertn.) following defoliation

Effects of defoliation of crested wheatgrass (Agropyron cristatum [L.] Gaer tn.) on the amount of time required to reach peak regrowth, the lag period for regrowth to begin, regrowth biomass, tiller survival and replacement, a nd carryover effects of defoliation the following year were investigated. R egrowth of crested wheatgrass was determined during the summers of 1990, 19 91 and 1992 in central Saskatchewan following a single defoliation to a 5-c m stubble height at eight stages of growth. Crested wheatgrass regrew 54-13 0 g m(-2) of biomass when defoliated tillers had less than or equal to 3.6 leaves. Regrowth began accumulating within 3-53 growing degree-days (GDD) a nd peaked in 705-875 GDD. Rates of leaf development after defoliation (218- 252 GDD phyllochron(-1)) equaled or were faster than control (218-330 GDD p hyllochron(-1)). Regrowth biomass accounted for 35-76% of total annual prod uction. Total annual production was greatest when plants were defoliated du ring vegetative growth or at peak growth. In 1991 and 1992, etiolated growt h in the spring following defoliation was reduced by defoliation in the pre vious year. Tiller replacement was not affected by defoliation and averaged 1.2 tillers tiller(-1) (SE = 0.1) in 1991 and 1.5 tillers tiller(-1) (SE = 0.1) in 1992. Two periods of grazing can be expected from crested wheatgra ss if it is grazed when tillers have less than or equal to 3.6 leaves; howe ver, the impacts of second grazing must be determined. If crested wheatgras s is grazed late in the growing season, only one period of grazing can be e xpected, and production will likely be less the following growing season, n ecessitating a rest period for plants to regain their production potential.