INFLUENCE DE L’HUMIDITÉ DU SOL, DE LA TEMPÉRATURE ET DE LA DURÉE DU GEL SUR LA SURVIE DE LA LUZERNE

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 moist...