A re-evaluation of crop heat units in the maritime provinces of Canada

Crop heat units (CHU) are commonly used to rate suitability of corn (Zea mays L.) hybrids and soybean [Glycine max (L.) Merrill] varieties for production in various regions of Canada. The CHU map presently in use for the Maritime provinces is based on climate data from the period 1956 to 1985. This paper presents an updated CHU map for the region using the latest available climate normals (1971 to 2000) and up-to-date interpolation and mapping procedures. Decadal time trends of CHU and water deficits are also examined for seven selected climate stations in the region. Average CHU ratings often increased by 100 units or more for the most recent period, with some exceptions. Station decadal trends from 1955 to 2004 confirmed the warming trend, with an average increase of 86 CHU per decade. Increased CHU have promoted higher potential yields in corn and soybean in the region, although this potential was not likely met during the last decade due to frequent droughts in some areas. However, there is presently little evidence to suggest that higher yield potential will be significantly limited by changing water deficits as a result of greenhouse-gas induced global warming in this century.