• DSSAT CSM-CROPGRO was adapted for perennial tree phenology modeling, the TreeGRO. • TreeGRO was applied to sweet orange, with four cultivars created. • Code changes comprised the first flower induction model within DSSAT framework. • The flowering model presented a MAE of 15 days. DSSAT is a widely recognized tool for crop modeling that has been utilized worldwide. However, the system currently lacks a model for perennial fruit trees. Sweet orange cultivation is of great importance to many countries, including both Brazil and the USA, and a process-based model could provide invaluable support for planning and decision-making. Hence, the goal of this study was to adapt the CSM-CROPGRO module in DSSAT for sweet oranges, potentially enhancing its representation for the simulation of tree fruit phenology. Model adaptation was divided into three phases: (i) literature search for basic physiological data, along with experimental data and observations for calibration; (ii) model development and adaptation through modifications of TreeGRO, a first version of a model for sweet orange, and (iii) a sensitivity analysis of the critical parameters that define phenology. Model adaptations were made in (1) model code for season initialization, (2) cardinal temperatures for development processes, and (3) model code for flower induction. TreeGRO has been incorporated into the CSM-CROPGRO Version 4.8.5 of DSSAT showing promising results after phenology and perennial representation improvements. There was a good simulation of anthesis (MAE of 14 days), which is consistent with the natural variability of citrus flowering that typically occurs over a multi-day to multi-week window within field orchards. Additionally, the sensitivity analysis demonstrated coherent and site-specific responses of simulated anthesis dates to changes in minimum air temperature and the precipitation threshold. However, maturity simulation still requires further refinement, as this phenological phase is characterized by a prolonged harvest window rather than a discrete phenological event. This limitation is further intensified by the scarcity of complete citrus phenological datasets and by the data requirements of process-based models such as CROPGRO, which relies on detailed physiological and environmental observations for robust calibration. Future work should seek detailed high-quality data for model improvement and further evaluation with data representing different production environments and cultivars for growth and yield estimation. The CSM-TreeGRO is a promising, robust, and ready-to-use tool for simulating sweet orange development within the open-source DSSAT framework.
Rasera et al. (Wed,) studied this question.