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Assessing Thermal Indices for Modeling Grain Corn Phenological Development on the Prairies.

Zhanda, J., Bullock, P.R., Zvomuya, F., Lawley, Y., Reid, L.M., Flaten, D. 2017. Assessing Thermal Indices for Modeling Grain Corn Phenological Development on the Prairies. 70th Northeast Corn Improvement Conference, Ottawa, ON, Feb 21-22, 2017. Oral presentation.


Studies have shown some positive trends in heat unit accumulation in recent decades, increasing the feasibility of grain corn production in cooler regions, such as the Canadian Prairies. Furthermore, producers require a reliable measure for prediction of corn development. A two year field study was initiated in 2015 at six locations in Manitoba and two locations in southern Alberta to quantify heat unit requirements to reach specific developmental stages among five corn hybrids with different maturity ratings. The objective was to identify a thermal index with a consistent accumulation for corn phenological development on the Prairies. The indices assessed included the corn heat unit (CHU), the growing degree day with a base temperature of 10°C (GDD10), the modified growing degree day with a base temperature of 10°C and maximum temperature of 30°C (mGDD10, 30), the General Thermal Index (GTI) and days after planting (DAP). The experiment was laid out as a randomized complete block design with site-year as the block, and therefore a random factor, and corn hybrid as a fixed factor. Daily maximum and minimum air temperatures were obtained from onsite automated weather stations to compute the amount of heat required by corn to reach each phenological stage. Corn development from emergence (VE) to silking (R1) was monitored by time lapse cameras set adjacent to each plot and taking pictures at three-hour intervals. Physiological maturity (R6) was defined by the presence of a black/brown layer at the tip of corn kernels. A non-destructive MT808 Electrophysics moisture meter was used to measure weekly kernel moisture content until physiological maturity. The expectation was that the corn hybrids would have significant differences in heat accumulation, especially at physiological maturity. However, there were no significant differences in heat unit accumulation among the five corn hybrids for reaching all phenological stages of development, regardless of the index used in the evaluation. Overall, the five corn hybrids required more CHU than their ratings to reach physiological maturity. The cumulative values for all thermal indices at R6 had a coefficient of variation < 10% but GTI had the lowest (<5%) regardless of the hybrid. The low CV for GTI indicated that the index may be more consistent than other indices in predicting phenological development of corn. Also, the GTI continued to accumulate late in the season, when air temperatures were low, whereas the other indices stopped accumulating. It was clear that the corn also continued to mature under cool temperatures late in the season. The superior performance of the GTI may be related to its more accurate simulation of late season corn development. Additional site-years, especially for early maturing corn hybrids are needed to delineate statistically significant differences in heat unit accumulation by hybrid. Producers are also interested in further evaluation of commercial corn hybrids to assist in selection of appropriate hybrids for their area of production.

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