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 (GDDi) 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

Ecophysiological Yield Components of Maize Hybrids with Contrasting Maturity

“…The evaluated hybrids showed different duration of the emergence–flowering and flowering–physiological maturity stages. These results differ from those observed by Derieux and Bonhomme (1982a, 1982b) for the North region of Europe and by Major et al (1983) in Canada, who found that the differences in the hybrid cycle were mainly explained by changes in the duration of the period from emergence to flowering. Differences in durations of the grain‐filling period among hybrids were also found by Maddonni et al (1998)…”

Delayed Planting Effects on Flowering and Grain Maturation of Dent Corn

“…For example, the correlation coefficient between mean daily maximum temperatures (May through September) and the GDDAP‐R6 intervals for the hybrid 3394 was equal to 0.82 (12 environments). Several previous researchers (Aspiazu and Shaw, 1972; Major et al, 1983; Sutton and Stucker, 1974) have reported similar relationships. Thus, the hybrids appear to have the capacity to adapt to shorter‐season environments.…”

Phenological Temperature Response of Maize

“…The reproductive period (silking to physiological maturity), measured in days, is less variable than the vegetative period (Derieux and Bonhomme, 1982b); therefore, temperature response studies have focused on the vegetative period (e.g., Bonhomme et al, 1994). However, thermal-time concepts, such as the GDD and CHU, have been less useful for the reproductive period, because thermal time required for specific genotypes to reach maturity has been found to vary with the thermal environment (represented by mean daily air temperature) (Major et al, 1983;Plett, 1992).…”