SCALES: A Computer Program to Convert among Three Developmental Stage Scales for Wheat

The Haun, Feekes, and Zadoks-ChanpKonzak developmental stage scales are often used to report phenological information for wheat (Triticum aestivum L.) development. Agronomists familiar with one of these scales may have only a passing acquaintance with developmental scales other than the one they consider most appropriate for their purposes. This makes review and interpretation of the literature more difficult. Although wheat development models often report phenological results, they generally use no more than one scale. For these reasons, and because there is not a simple numeric correspondence among the three scales, a computer program to convert among them is a useful tool. SCALES is a three-module FORTRAN program that relates the three scales based on published descriptions. The interactive user interface module requests an input scale value and minimal additional information, which the conversion module uses to determine values for the remaining two scales via a dichotomous key. The output module writes the conversion results to the monitor. SCALES may be used independently for comparing phenological data based on different developmental scales, or the conversion module may be incorporated into computer models to provide output of developmental stage information for the simulation. D EVELOPMENTAL STAGE SCALES are widely used to report the phenology of wheat. These scales provide an easily understood means of assessing developmental progress and are useful in comparing the effects of different management practices and environmental conditions. The timing of management practices, such as herbicide application, is often based on the stage of crop development. Agronomists use different scales, making the review and interpretation of the literature difficult because the reader must convert results to a familiar scale for comparison. Wheat simulation models often incorporate at least part of existing phenological development stage scales into their programs. Scale values are helpful in evaluating the effects of changes in crop and environmental parameters. They may also be used in model validation and in comparing results of different models. Attaching a developmental scale stage to a modeled canopy provides a convenient way for the model user to visualize the "crop" which exists only in computer memory. In many models, such as CERES-Wheat (Ritchie, 1985; Godwin and Vlek, 1985), WINTERWHEAT (Baker et al., 1985), and TAMW (Maas and Arkin, 1980), phenological status is reported by identifying D.M. Harrell, Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583; W.W. Wilhelm, USDA-ARS, De . of Agronomy, Univ. of Nebraska, Lincoln, NE 68583; G.S. h fc~as te r , USDAARS, Great Plains Systems Res., P.O. Box E, Fort Collins, CO 80522. Joint contribution of USDA-ARS and Nebraska Agric. Res. Div. Published as Journal Series no. 9961, Agric. Res. Div., Univ. of Nebraska. Received 21 May 1992. *Corresponding author. Published in Agron. J. 85:758-763 (1993). major developmental stages (e-g., tillering, jointing, booting) rather than calculating a numerical scale value. Other models, such as ARCWHEAT (Weir et al., 1984), report development on a single scale, Haun (Haun, 1973) in this case. Few models report more than one scale; however, SHOOTGRO 2.0 (Wilhelm et al., 1990) and MODWHT (Waldman et al., 1990) report phenological results using the Haun, Feekes (Large, 1954), and Zadoks-Chang-Konzak (ZCK; Zadoks et al., 1974) scales. The Feekes, Haun, and ZCK scales are the most widely used for wheat. The Feekes and ZCK scales are descriptive, nonlinear scales based on irregularly spaced phenological events from planting (ZCK) or emergence (Feekes) to plant maturity. The ZCK scale is essentially an expansion of the Feekes scale to provide more detail and wider geographic applicability. In contrast, the Haun scale is continuous and approximately linear in time and thermal units. It extends from emergence to anthesis. The Haun value at each phenological stage is not fixed but reflects the number of leaves ~roduced on the main stem prior to the current time; thus it is strongly influenced by cultivar, planting date, management, and environmental conditions. These differences prevent a simple numeric correspondence among the three scales, particularly between the Haun scale and the other two. For this reason, conversion between scales requires knowledge of wheat phenological development and the scales themselves. The three scales differ in approach to stage designation and in level of detail. Consequently, they differ also in the applications to which they are best suited. Hence, it is likely that all three will continue in use and there is benefit in developing ways to convert and correlate the scales. Because many agronomists may have only a passing acquaintance with developmental scales other than the one they consider most appropriate for their purposes, and wheat development models generally report results using no more than one scale, we identified a need for a computer program to aid in the conversion between developmental scales. Such a program could make it easier to interpret experimental and simulation results reported on an unfamiliar scale and to report results using more than one scale. The purpose of this paper is to describe the computer program, named SCALES, constructed to convert information on wheat development from emergence to maturity, among the Feekes, Haun, and ZCK scales. PROGRAM DESCRIPTION AND EXECUTION