MONTHLY CLIMATIC CONTRIBUTION TO THE WINTER INJURY OF ALFALFA

Abstract

A technique was developed to determine the long-term climatic contribution of each month to the winter injury of alfalfa from the start of growth in May to the end of the dormant period in April the next year. The basic hypothesis was that this contribution is proportional to the number of climatic variables (single or combined) showing a significant difference between the years of higher and lower survival, i.e. to the number of variables affecting survival. The variables were related to soil and air temperatures, soil frost depth, hours of sunshine, and rain and snow regimes. Annual curves of the monthly numbers of significant variables for Swift Current and La Pocatière were similar. Converting the number of significant variables into terms of relative winter injury, the critical months at Swift Current were: May, contributing to winter injury by 12%; October (12%); December (19%); March (11%); and April (22%). At La Pocatière, they were: May (12%); November (15%); January (10%); March (10%); and April (33%). The similarity in the relative importance of various months at both sites indicated that alfalfa survival is more particularly influenced by the climate during certain phases of its life cycle.