Development, calibration and validation of a greenhouse tomato model: 1. Description of the model.

A dynamic crop growth model, TOMGRO, for an indeterminate tomato variety is presented. The model describes the phenological development and increase in dry weight of various organs (roots, stem nodes, leaves and fruits) from planting till maturity under variable environmental conditions. Phenological development is governed by genetic plant properties and environmental conditions (e.g. air temperature and CO2 level) and expressed in a plastochron index, i.e. the current stem node number. Total dry matter accumulation is based on a quantitative description of the carbon balance, including gross CO2 assimilation, maintenance respiration and growth respiration. Partitioning of dry matter increase over the various organs is governed by their relative sink strengh, defined on the basis of a genetically determined ‘potential’ growth rate, achieved under non-limiting carbohydrate supply. The model is both schematic and modular in set-up. This means it can be adapted easily and most of its subroutines can be replaced easily by others if better descriptions become available. It can also be combined with a more comprehensive model describing greenhouse climate and appears robust for use in procedures of economic optimization of climate conditions in greenhouses or for management purposes.