AN EVALUATION OF THE CORN HEAT UNIT SYSTEM FOR THE SHORT-SEASON GROWING REGIONS ACROSS CANADA

Abstract

A study was conducted at 11 locations across Canada to determine if corn hybrids have different corn heat unit (CHU) requirements in different climates. The study included six hybrids, four each in the three years 1977–1979. Differences in the time between planting and emergence were attributable to slow emergence of two hybrids as well as management and weather factors at different locations. Genotypic differences were expressed mainly in the period between emergence and anthesis. At three locations, 198 CHU more were required than at other locations. In the period from anthesis to 45% ear moisture, two hybrids required more CHU than other hybrids. These extra CHU requirements were not related to hybrid rating, i.e., late-maturing hybrids did not require more CHU to complete the ripening phase. In a comparison of growing degree days (GDD i ) with bases ranging from 5 to 15 °C, no one thermal unit had sufficient advantage over the CHU system to warrant its adoption in Canada. Further, calendar days were the best for predicting the duration of the period from planting to emergence. The period from emergence to 10% anthesis was least variable of all the stages and could be predicted accurately by any of the methods.Key words: Zea mays, temperature, adaptation, thermal units