GENERATION OF MECHANISTIC VARIABILITY IN A PROCESS-BASED OBJECT-ORIENTED PLANT-MODEL

A cotton crop model based on individual plant developmental behavior a nd variability was developed. Object-oriented simulation (OOS) provide d the conceptual basis for the new model structure. The procedural mod el, COTSIM, provided the theoretical background for cotton plant devel opment. Data collected during 1987 from field-grown cotton were used f or model development and verification, and data from 1988 were used fo r model validation. The model predicted mass accretion and production of organs within the patterns and magnitudes observed in the field. Th e model also predicted crop development aspects that had not previousl y been described by procedural models. Age and size of leaves and frui t and associated developmental variability were included in the model through representation of objects and their variable behavior defined by their position on the plant and how this constrains their growth. O bserved variability was the result of the aggregate behavior of compon ents. Variability in our OOS model is an output as opposed to being an input in most procedural plant models. The model has recreated both r ealistic plants and populations in a mechanistic simulation. Object-or iented models are an important step towards common structures and lang uages for model design and the development of simulations. It was note d that increased mechanistic detail resulted in an increase of procedu re calls (messages) and a five-fold increase in model run time.