| Brendan L. Kowalenko and J.T. Romo |
| Authors are former graduate student and professor, Dept. of Crop Sci. and Plant Ecology, 51 Campus Drive, Univ. of Saskatchewan, Saskatoon, Sask. S7N 5A8. JTR is corresponding author. |
Abstract |
| Freezing temperatures in winter were hypothesized to be a major cause of mortality of tillers following defoliation of northern wheatgrass (Agropyron dasystachyum [Hook.] Scribn., syn. Elymus lanceolatus [Scribn. & Smith] Gould). Cold-hardiness of northern wheatgrass tillers was determined following a single mowing to a 5-cm stubble height in late May, June, July, or August in 1992 or 1993 in southwestern Saskatchewan. An unmowed control was also included. Cold-hardiness was determined in early and late winter immediately following mowing by: 1) exposing tillers to controlled temperatures ranging from 3 to o-36oC, or; 2) exposing them to 15oC for 0 to 15 days. The LT50 (temperature at which 50% of tillers died) of northern wheatgrass tillers in early winter ranged from 29.5 to <36.0oC in 1992-93, and averaged 24.0oC in 1993-94. In late winter LT50 ranged from -18.1 to 22.6oC in 1992-1993, and it averaged -22.0oC in 1993-1994. The LDur50 (duration at which 50% of tillers died) of tillers exposed to 15oC for 0 to 15 days ranged from 8.0 to 13.1 days in early winter, and 2.7 to 4.7 days in late winter. Unexpectedly mowed tillers were generally more cold-hardy than those from control. In early winter LT50 was 1.5 to 10oC lower for mowed than control tillers. The hypothesis that defoliation reduces cold-hardiness of northern wheatgrass was rejected. The degree or duration of cold stress in the field is generally insufficient to reduce tiller survival in northern wheatgrass. Late winter through early spring is a critical period for tiller survival of northern wheatgrass because cold-hardiness declines this time of the year. Maintaining insulating cover can moderate soil temperatures and reduce damage to plants from freezing temperatures. |
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Keywords: Agropyron dasystachyum (Hook.) Scribn., cold stress, crown temperatures, Elymus lanceolatus (Scribn. & Smith) Gould, freezing tolerance, grazing, Northern Mixed Prairie, tiller survival |