THE EFFECT OF TEMPERATURE, MOISTURE AND NITROGEN ON THE RATE OF DEVELOPMENT OF SPRING WHEAT AS MEASURED BY DEGREE DAYS

Abstract

A phenological index based on meteorological parameters that accurately describes the development of wheat is urgently needed by agricultural researchers. In this study, a biometeorological time scale was proposed. It was developed from data obtained in a growth chamber study in which the effect of temperature, N fertility and soil moisture on spring wheat (T. aestivum L.) development were assessed. The model was then proffed using data from 2 field experiments. A normalized time scale was derived relating phenological development to percent SD, defined as ((number of days to a selected phenological stage)/(number of days to soft dough)) .times. 100. The degree day equation was modified to incorporate this time scale as: .**GRAPHIC**. where K1 is a rate constant having units % SD .cntdot. .degree.C-1 .cntdot. day-1; b0 is a base temperature below which no development occurs with units .degree.C; and Tm is the mean daily temperature between growth stages S1 and S2. This equation was used to derive values for the developmental parameters. In the growth room K = 0.0875 (SE 0.0045) and b0 = 4.6 (SE 0.99). Under field conditions K1 = 0.0935 (SE 0.0123) and b0 = 2.4 (SE 2.213). The growth room and field parameters were not significantly different at the 5% probability level. Temperature was the only environmental parameter which influenced the rate of development under the conditions of this experiment. The number of days to the various developmental stages was inversely and linearly related to mean daily temperature over the 15.degree.-25.degree. C range. The degree day equation was a good index of development. Under field conditions the number of degree days to progress a crop to the flowering stage was 703 (SE 9.4) and to the soft dough stage 1086 (SE 15.4). The small variability in the values of the developmental parameters obtained in the growth room and field experiments were attributed to errors in the determination of phenological dates, and differences between temperature in the crop microclimate and measured temperatures from the standard meteorological site. A further modification to the degree day equation was postulated to account for the influence of day length on wheat development.