A General Thermal Index for Maize

Abstract

with location and year (Major et al., 1983;Plett, 1992). Most frequently, the GDD concept overestimates the Thermal indices predict and describe development rate more accuheat units required for grain filling (Dwyer et al., 1996). rately than time in days and are commonly used to rate maize (Zea mays L.) for maturity. Separate temperature response functions for This is particularly evident in years with below-normal the vegetative and grain-filling periods predict more accurately time temperatures, when maturity estimates using GDDs to maturity than a single function for the two periods combined. may be several hundred heat units too high (Roth and However, use of two functions requires a priori knowledge of the Yocum, 1997). silking date, which becomes the transition date from the vegetative Recently, separate temperature response functions function to the grain-filling function. The objective of this study was have been developed for the vegetative and grain-filling to evaluate the sensitivity of estimates of silking and maturity dates periods of maize (Stewart et al., 1998). These equations, to the transition date between vegetative and grain-filling functions which were fitted to data from 28 hybrids collected at and to develop a protocol to combine the two temperature response 19 locations ranging from 39Њ to 48Њ N lat over 4 years, functions in a general thermal index (GTI) for maize. Frequencydiffered from those assumed by GDD and CHU and distributions of mean daily air temperatures for five 20-d periods spanning mid-June to late September at 19 locations in the northern also from each other, especially at temperatures below USA and southern Ontario from 1992 to 1995 indicated few days 15ЊC. Use of the fitted response functions reduced stan-(Յ12%) with mean daily air temperatures less than 15؇C before late dard errors in estimating the entire period from plantingAugust. This was significant, as the two response functions diverged to maturity by 50% compared with GDD estimates, significantly at temperatures below 15؇C. Standard errors in estimating with a reduction in the standard errors in estimating the maturity date using different transition dates remained small (Ͻ7.5

Evaluation of the STICS crop growth model with maize cultivar parameters calibrated for Eastern Canada

“…According to the study by Dwyer et al (1999), the estimated duration of the growing season was about 5-8 days longer in Woodstock (southern Ontario, 150 km northeast of Woodslee) than in Ottawa. Most of this increase was due to a longer duration of grain filling.…”

Base Temperatures for Seedling Growth and Their Correlation with Chilling Sensitivity for Warm‐Season Grasses

“…There is, therefore, a need to use different base temperatures for different species and ecotypes, and these were corroborated by chilling sensitivities. Adoption of different base temperatures can only improve the predictive growth equations reported by Sanderson and Wolf (1995b), Mitchell et al (1997), and Sanderson and Moore (1999) It is also conceivable, as in maize (Stewart et al, 1998; Dwyer et al, 1999), that there are different thermal functions for different growth stages. These different stages might require different base temperatures.…”

Climate Warming Trends in the U.S. Midwest Using Four Thermal Models

“…Accumulation of TT in the CHU model begins at 4.4°C with no upper temperature boundary, although high temperatures result in a reduced accumulation of TT. The GTI model has two different equations based on crop developmental stage with silking date as the transition (Stewart et al, 1998; Dwyer et al, 1999a). The vegetative model follows a sigmoidal curve starting below a mean temperature of 5°C and maximum accumulation between mean temperatures of 25 and 30°C.…”