Factors affecting cold resistance in winter wheat

All studies dealing with factors affecting cold resistance in winter wheats were conducted with field-hardened plants. Varieties of wheat, varying widely in winterhardiness, were grown in 4-inch pots or flats in the field and were subjected to controlled freezing tests at regular intervals throughout the winter months. Continuous soil and air temperatures under field conditions were recorded. A good agreement was found between results of artificial freezing and field tests. The temperature of the soil under a layer of ice was found to be closely associated with atmospheric temperatures. Soil protected with 3 to 5 inches of snow showed small changes in temperatures. A spread of 44 degrees F was recorded between the temperatures of the air and snow-covered soil. Ice-covered soil reached lower temperatures than that covered with a layer of snow. Wheat plants repeatedly acquire and lose their hardiness, depending upon the atmospheric temperatures during the winter months. Variations in level of hardiness were found from week to week, season to season, and among varieties. Wheats vary in their degree of cold resistance, ability to accumulate hardiness, and to acquire the hardened condition earlier in the fall and retain it later in the spring. Wheat seedlings possessing from 5 to 15 leaves per plant were the most cold resistant. Germinated seed to seedlings with two to four leaves and plants 10 to 12 inches tall were quite susceptible to cold. Under the conditions of these experiments, wheat seedlings grown on low and medium levels of fertility differ little in their cold resistance. The seedlings grown on high levels were large and succulent and showed the greatest injury. Since soil fertility greatly influences plant development, which in turn affects cold resistance, it appears that the fertility of the soil has an indirect effect on cold resistance. Wheat plants of five varieties infested with hessian fly were more susceptible to freezing temperatures than non-infested plants.