Modeling Phenological Development of Corn: Do Corn Heat Units Work in the Prairies?.

Corn (Zea mays) is a warm and long season crop that requires adequate heat for growth and development. Recent positive trends in heat unit accumulation over the last several decades in western Canada may increase corn production potential in cooler regions such as the Canadian Prairies. A two-year field study was initiated in 2015 at six locations in Manitoba and two locations in southern Alberta to determine if corn heat unit (CHU) accumulation is consistent by location for a defined set of phenological stages and corn hybrids with different CHU ratings. A second objective is to evaluate the influence of low temperatures on leaf tip appearance, hence phenological development of corn. The experiment was laid out as a randomized complete block design with site as the blocking factor and corn hybrid as a fixed factor. Daily heat unit accumulation from an automated weather station at each location was used to determine the amount of CHU accumulated by each corn hybrid at each phenological stage. Corn development was monitored by time lapse cameras set adjacent to each plot and taking pictures at three hour intervals. Physiological maturity was considered attained when kernel moisture content reached 31-35 % (which coincides with black layer formation), as determined with an MT808 Electrophysics moisture meter. Results from 2015 showed no significant differences in CHU accumulation among three hybrids with similar CHU ratings (2550, 2600, 2700) at all phenological stages, except at the tassel stage for which hybrid 2700 accumulated significantly more CHU (1476 ± 90) than hybrid 2550 (1307 ± 80 CHU). There was a positive correlation (r = 0.53) between weekly leaf tip appearance and CHU. However, leaf tip appearance did not differ significantly (P = 0.06) among the three corn hybrids in 2015. For 2016, two additional hybrids with CHU ratings of 2200 and 2350 are being added to the study at the same locations to provide a wider range of corn hybrid CHU ratings in the evaluation. CHU index will also be evaluated with growing degree days, general thermal time index and thermal leaf units to determine if it is a more accurate predictor of phenological development of corn in the Prairies. An accurate and reliable measure of corn phenological development in cool growing regions such as western Canada would help producers to reduce risk in selecting hybrids best adapted for grain production at their particular locations.

 Keywords: Zea mays L., corn, phenology, corn heat units, modeling, leaf tip appearance, growing degree days, general thermal time index, thermal leaf units