EFFETS DE CERTAINS FACTEURS CLIMATIQUES ET EDAPHIQUES SUR LA SURVIE A L’HIVER DE LA LUZERNE AU QUEBEC
A comparative study conducted for the winters of 1973–74 and 1974–75 in three zones of the Province of Quebec permitted us to point out the principal climatic and edaphic factors in the winterkilling of alfalfa fields. Alfalfa plants were sampled on 21 different location–years in order to measure their potential yield index (IRP) and the heaving index (ID) of the tap root. Climatic conditions were suitable for the survival during the winter of 1974–75. Yet, during the winter of 1973–74, alternate freezing and thawing, rainfall and the lack of snow cover gave significant differences between the three zones. The IRP increased from the South (zone I) to the North (zone III) of the province. Partial correlations analysis emphasized the importance of rainfall on soil water (r = 0.58) and on snow depth (r = 0.79). Stepwise regression analysis showed that the change in soil water content during the winter was the variable which had the greatest impact on the IRP and the ID. These field experiments suggest the development, on a national basis, of an agrometeorological and statistical survey system to assess alfalfa crop injury and to recognize regional differences.