Modeling Preemergent Maize Shoot Growth: I. Physiological Temperature Conditions

Abstract

Prediction of seedling emergence is an important first step in predicting crop establishment. There are numerous models that, under nonlimiting seedbed physical conditions, can adequately predict time to emergence using heat sums based on average daily temperatures. Under more adverse seedbed physical conditions, however, such as occur in the semiarid tropics, use of such coarse indices will tend to obscure the strong influence that even temporary extremes in soil temperature or strength can have on the time and extent of emergence, yet it is in these situations that final crop establishment and ultimately yield will be particularly sensitive to emergence predictions. One way to quantify the effect that temporary extremes in seedbed conditions have on emergence is to model the emergence process (namely, preemergent shoot growth). In this paper, we model preemergent maize (Zea mays L.) shoot growth as a first step in characterizing seedling response to a high soil temperature and strength environment. The model, developed from shoot length data obtained under constant temperature conditions ranging from 20 to 40°C, uses an exponential function that predicts coleoptile and first internode growth rates as a function of temperature and sums the output to predict shoot length. Comparison of model predictions with independent measurements carried out in the 20 to 40°C range show that the model is capable of accurately simulating preemergent shoot growth under conditions where (i) temperatures are constant with time, (ii) temperatures of the whole seedbed vary diurnally, and (iii) temperatures within the seedbed vary with time and depth in the seedbed. However, the model was unable to predict shoot growth in situations where seedlings had been exposed to temperatures in excess of 40°C, indicating that further work is needed to assist modeling within the high temperature range.

Sink-pulled simulation of the maize crop

“…Maize-S simulates seedling emergence according to the method of Weaich et al (1996), leaf area growth according to the method of CERES-Maize (Jones and Kiniry, 1986), gross photosynthesis according to the method of Goudriaan and van Laar (1978). This method was modified to account for the effect of temperature on ma.ximum leaf photosynthesis according to the method that is used in MACROS (Penning de Vries et al.…”

“…In addition, high temperature causes pollen sterility (Saini and Aspinall, 1982) and might causes asynchronous silking of the ears relative to pollen shed (Jacobs and Pearson, 1991). Weaich et al (1996) developed a model to predict maize seedling emergence by using an exponential function to predict coleoptile and first intemode growth rates as a function of temperature, and summing the output to predict shoot length. CEEIES-Maize predicts seedling emergence and the subsequent phenological stages using growing degree days (the sum of average daily temperature above base temperature) because of the effect of temperature on developmental stages in maize.…”

“…Moreover, the model responds to temperature stress. In summary, the developed model simulates seedling emergence using the method of Weaich et al, (1996). During vegetative growth, the model uses heat sums based on die average daily temperature and base temperature (lowest temperature under which growth occurs) to determine the time of each development stage.…”

“…Emergence is attained by rapid mesocotyl (first intemode) elongation, which pushes the growing coleoptile to the soil surface (Ritchie et al, 1993). Prediction of seedling emergence is an important first step in predicting crop establishment (Weaich et al, 1996). CERES-Maize predicts seedling emergence using heat sums and planting depth.…”

“…Moreover, the previous method does not simulate germination of maize seed; it only predicts emergence date. Weaich et al (1996) developed a model to simulate maize germination by predicting coleoptile and first intemode growth rates as a function of temperature, and sums the output to predict shoot length. For more realistic simulation of germination, I decided to use this second method in Maize-S. To determine the time of seedling emergence, both coleoptile length and first intemode length are calculated and summed.…”