Document Type : Research Paper
AgWeatherNet, Washington State University, Prosser, WA 99350-8694, USA.
Department of Crop and Soil Sciences, The University of Georgia, Griffin, GA 30223, USA.
Development of wheat (Triticum spp.) is primary driven by temperature, but is
also affected by other factors such as vernalization and photoperiod. Crop growth
and development are often described in terms of calendar days. However,
determining the development in terms of thermal time or physiological time is
more accurate because it is an accumulation of the caloric energy needed for the
occurrence of phenological stages. The objectives of this study were: (i) to
determine the base temperature for key phenological stages of different winter
wheat cultivars and (ii) to develop a phenological model using the base temperature
for predicting the duration in terms of thermal time for different phenological
stages. Eight wheat cultivars were selected according to their vernalization period
to determine the base temperature for three critical developmental phases, i.e.,
planting to heading, heading to harvest and planting to harvest. For each cultivar,
the base temperature for each critical period was estimated as well as the duration
of the three key phenological stages in terms of thermal time for three locations in
Georgia from 1999 to 2010. The base temperatures and the growing degrees varied
widely depending both on the developmental stage and the cultivar. The estimated
base temperatures for the eight wheat cultivars ranged from 3.1 to 8.1 oC, 10.6 to
18.4 oC and 1.6 to 8.4 oC, for planting to heading, heading to harvest maturity and
planting to harvest maturity. Also, the duration in Growing Degree Days (GDD)
was determined for each season and cultivar. When 0 oC was used as the base
temperature, the GDD between cultivars varied from 1675-1844, 1017-1239 and
2827-2936 oC from planting to heading, heading to harvest maturity and planting to
harvest maturity, respectively. The results from this study provided specific base
temperatures for each developmental stage for each individual cultivar and,
therefore, provided a more accurate estimation of GDD. The variation in base
temperature and GDD accumulation is probably a selective advantage for winter
wheat. Clearly more work is required to estimate the base temperatures and
duration for others phenological stages and further evaluation is required for
additional cultivars and a wider range of environments.
Keywords: Growing degree days; Development; Phenology.