PHYSIOLOGICAL FACTORS OPERATIVE IN ICE-SHEET INJURY OF ALFALFA

Abstract

Ice-sheets that contact the surface parts of herbaceous plants for extended periods are among the most injurious of the climatic hazards of many overwintering crops. Under field conditions they occur primarily in low spots which are not well drained. They may, however, cover large areas regardless of topography because sleet storms prevail in latitudes between those regions which are snow-covered for the major portion of the winter and those which, for the most part, are bare. Knowledge of the nature of ice-sheet injury is limited, and the work reported here is quite preliminary. It is an attempt to ascertain under controlled conditions some of the basic physiological factors which cause this type of winter injury. It has been suggested that killing by ice-sheets is due to smothering. The exact meaning or interpretation which that word was intended to convey is not clear. Bugaevskii and Zitnikova (1) have observed that winter wheat plants beneath an ice crust at -Io C. to -9? C. began to decrease in vigor after the twenty-third day and in fifty-four days all were dead. They suggest a lack of oxygen as a possible cause of death. On the other hand, smothering might be construed to mean the absence of a free diffusion of substances from the organism into the pore spaces of the soil and into the air or conversely, from the air to the organism. Whatever the interpretation of the term may be, efforts to break the ice cover and to eliminate its sealing effects by mechanical means such as disking and other types of scarification, have not proven effective in reducing or preventing icesheet injury under field conditions. In 1922, Graber scarified alternate areas of an ice sheet on an alfalfa field in with a weighted disk. Although the scarification occurred within four days after the formation of the ice-sheet the alfalfa was badly killed whether the ice was broken or allowed to remain intact. He further observed that during the first three months of 1937, a sheet of ice, frozen tightly to the soil surface, covered most of the southeastern quarter of Wisconsin. In desperation, many farmers scarified this ice cover with disks and other farm implements. In no case was such treatment reported as being helpful and the losses from winter-killing of alfalfa that year were in excess of 200,000 acres. Only where an interveni Contribution no. 151 from the Department of Agronomy, Wisconsin Agricultural Experiment Station, Madison, Wis. Published with the approval of the Director of the Wisconsin Agricultural Experiment Station.