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Crop growth simulations are needed to help organize our knowledge of plant response to the environment for the purpose of assisting growers in management decisions, predicting impacts of land use decisions, and predicting the consequences of probable climatic variation. This paper describes the derivation, combination, and (where necessary) calibration of the models required to produce a simulation of the seasonal development and growth of winter wheat. The simulation provides appearance time and size estimates for each aboveground plant part (leaves, stems, spikes, and kernels), length and mass of roots with depth, time of occurrence of phenological events (germination, emergence, tillering, single ridge, double ridge, jointing, boot, heading, anthesis, soft dough, mature, and harvest ripe), rate and amount of water evaporated and transpired, uptake of N from the soil profile, and estimates of daily net photosynthesis. Strengths of the simulation include that it predicts dates for all crop phenological stages, it estimates sizes for all plant parts on a daily basis for comparisons with almost any observed field data, it is organized according to the natural structure of the system being simulated, and it is designed to be changed. Weaknesses include current lack of ranges for parameter values for different cultivars, a simplistic soil water budget, and limitations in specifying nutrient distribution among plant organs. No weed, pathogen, or insect models are incorporated; however, the program that implements the simulation is specifically designed to be easily modified, so pest models could be added.

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Dynamic crop simulations are used more and more frequently as research and education tools and to assist in making management decisions. MODCROP is an interface framework for controlling a dynamic simulation that simplifies applying the simulation. The program operates under DOS on an IBM‐compatible microcomputer (PC) with 640k of RAM and a hard disk drive. Although a math coprocessor is desirable, it is not required. It is constructed from modules written in Quick‐BASIC. Most of the modules can be reused without modification to provide user interface, data input, and data output services to compatible simulations. The framework allows data input or output in either metric or English units. Any parameter within a simulation under its control can be selected for output, depending on the wishes of the user. A simulation can be customized by interactive access to all initial parameter values and it can be operated in batch mode to determine patterns of predicted results. The framework is supplied with MODWht3, a daily simulation of organ‐by‐organ development and growth of winter wheat. MODCROP provides ease of use and simulation control features that are not always available in other simulation interfaces.

Timely field sampling of a developing crop requires careful organization of laboratory space, equipment, and personnel to maximize efficiency. This paper demonstrates how historical temperature data sets, planting dates, and plot site elevation and location can be used to project expected developmental stage for winter wheat (Triticum aestivum L.) plants at any site in the Pacific Northwest dryland wheat‐growing areas. Historical average temperature data from long‐term weather station records for over 50 sites in the Oregon‐Washington‐Idaho dryland cereal production areas are stored on a computer. A program selects the weather station site nearest to the plot site on the basis of latitude, longitude, and altitude. Average daily maximum and minimum temperatures from the weather station are used to generate daily growing degree days for the plot site. Growing degree days are used to predict crop development. Projections can be made of either the expected date for a particular developmental stage or the expected degree days for any given date. Projections are used to schedule sample dates.