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A field study was conducted to determine the effect of soil moisture on the survival of three winter cereal species. Treatments were applied by watering and weighing the soil to the desired water content. Plants were overwintered in a plastic greenhouse in 1988 and in 1989, in which the air was not heated, but the soil was slightly heated on cold days to avoid very low temperatures. Soil temperature did not fall below −16 °C. Soil temperature rate of change was dependent on moisture content. Puma winter rye and Otrastajuskaja 38 winter wheat were the hardiest, followed by Wintri winter triticale and Norstar winter wheat. Harus winter wheat was less hardy, and Champlein winter wheat was totally winter killed. The highest survival rate was obtained at moderate to high soil moisture content. The soil contained 44% water at field capacity and 19% at the wilting point. The drier the soil in the range 13–23%, the greater the mortality indicating a negative effect of long-term drought on plant survival. By contrast, the wettest treatments: 58% and partial ice encasement, did not reduce survival. However, total ice encasement killed 50–75% of the plants depending on the cultivar. There was an interaction between cultivar and moisture treatment. The data suggest that a moisture level intermediate between the wilting point and field capacity should be sought in studies of cold hardiness.Key words: Moisture, winterkill, ice encasement, wheat, rye, triticale

To determine how long hardened alfalfa (Medicago media Pers.) can survive in frozen potting mixture of various moisture contents, plants from two cultivars, the very hardy Rambler and hardy Apica, were hardened at 2.0 ± 1.5 °C for 3 wk. They were then frozer at −8 or −10 °C in potting mixtures of different moisture contents, for various time periods. In a first experiment with Rambler, the freezing time at which 50% of the plants survived (DGS50) in a potting mixture containing 40% moisture was 94.4 h at −8 °C and 17.6 h at −10 °C. In saturated (65% moisture) and flooded (85% moisture) mixtures, the DGS50 were 33.3 and 18.9 h at −8 °C, and 8.8 and 8.4 h at −10 °C, respectively. In a second experiment, both cultivars, Rambler and Apica, showed the same trends; the survival rate decreased more rapidly in wet potting mixture and at lower freezing temperature. DGS50 for Apica were shorter than those for Rambler. In freezing tests used to determine plant frost tolerance, not only are temperature and soil moisture important factors, but they also interact with freezing time to affect plant survival rates.Key words: Alfalfa, soil moisture, freezing, freezing duration, frost tolerance, frost survival