An appraisal of cereal crop phenology modelling

Abstract

of phenological development of cereal crops, primarily corn (ka nnys L.), wheat (Triticum aestivum L.) and har:ley (Hordeum vulgare L.), to environmental conditions was conducted. Examples of how these studies have been used to model phenological development on the basis of weather data were given.It was concluded that the develo,pment rate of most species is a sigmoidal rather than a linear function of temperanre. Consequently

A generalized nonlinear tempeature response function for some growth and developmental parameters in kiwifruit (Actinidia deliciosa (A. Chev.) C. F. Liang & A. R. Ferguson)

“…A typical biological response to temperature from T min to T opt follows a logistic curve (SHAYKEWICH, 1995). The response increases slowly as temperature increases from T min , it increases in a linear fashion at intermediate temperatures, and the rate of increase decreases as temperature approaches T opt , where the response is at a maximal.…”

“…Fourthly, the function (eq. 3) describes what is currently accepted in terms of temperature response of biological systems (SHAYKEWICH, 1995). At temperatures close to T min , the response is close to 0, the response increases in a linear fashion at intermediate temperatures, the response reaches a maximum when temperature approaches T opt , and the response decreases afterwards to 0 at T max .…”

“…At high temperatures, the catalytic properties of most enzymes are harmed and the total amount of enzyme present may fall as a result of increased rates of denaturation, and the reaction rate decreases to zero at T max (SHARPE & DeMICHELE, 1977). Therefore, close to T min and T opt , the response of biological processes to temperature is nonlinear (SHAYKEWICH, 1995).…”

“…The response of biological systems to temperature is linear in only a portion of the temperature range that affects biological processes, and is better summarized in terms of three cardinal temperatures, namely the minimum (T min ), optimum (T opt ), and maximum (T max ) temperatures (JONES, 1992;SHAYKEWICH, 1995). In this paper, T min is differentiated from T base to refer to nonlinear and thermal time approaches, respectively.…”

“…These modifications of the original way to calculate thermal time, however, are still not enough to overcome the empiricism of the approach because it is composed of a combination of linear equations, which introduces abrupt changes at the transition points of the response function. The response of plant processes to temperature is smooth and continuous, which can cause a significant departure from the linearity (SHAYKEWICH, 1995). The thermal time approach has also other disadvantages: (i) it is confusing how people implement the calculation of thermal time on a daily basis, i.e., sometimes the average daily temperature is subtracted from T base and sometimes the minimum and maximum temperatures are subtracted from T base and then averaged (McMASTER & WILHELM, 1997); (ii) it lacks generality because either the end points of the function, defined by T base , T opt , and T max , or the total number of °C for completing a given process or developmental phase are often dependent on genotype, and for many genotypes these values are unknown (McMASTER & SMIKA, 1998;KINIRY & BONHOMME, 1991).…”