MODWht3: A development-driven wheat growth simulation

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.