RELATIONSHIP OF DEVELOPMENT RATES OF CORN FROM PLANTING TO SILKING TO AIR AND SOIL TEMPERATURE AND TO ACCUMULATED THERMAL UNITS IN A PRAIRIE ENVIRONMENT
The effect of temperature on the phenological development of corn (Zea mays L.) was studied under field conditions at several locations throughout southeastern Manitoba, an area where the average annual corn heat unit accumulation is in the range 2100–2500. Twelve location years of data were collected from eight sites during 1980–1983. Two early-maturing hybrids, Pioneer 3995 and Northrup King 403 and one medium maturity hybrid, Pride 1108, were used. The duration from planting to emergence (PE) was predominantly controlled by soil temperature (ST). The duration from emergence to stem elongation (ESE) was significantly related to air temperature (AT), but not to ST. For both the PE and ESE growth phases, the thermal models — corn heat units (CHU), growing degree days (GDD) and modified corn heat units (MCHU) — were better estimators of duration than calendar days. The MCHU model, with threshold temperatures of 7 and 15 °C for the response functions to daily minimum and maximum temperature, respectively, estimated the duration of ESE more accurately than did the other thermal models. For the duration from stem elongation to silking (SESI), calendar days were better estimators than the thermal models. From emergence to silking (ESI), the thermal models using air temperature were generally better estimators of ESI duration than calendar days.Key words: Maize, thermal indices