The STICS model simulates how a system that includes plant cover and soil (the portion that is occupied by roots) works.

The atmosphere in the vicinity of the system is represented by a set of climate variables that are derived from standard measurements (generally collected by weather stations) and have a forcing function.

In functional terms, STICS uses a dynamic approach with a daily time step to simulate crop growth based on the carbon balance of plant : the radiation intercepted by the photosynthetically active system, characterized by leaf area index, is transformed into biomass partitioned among the various organs.

This partitioning of assimilates depends on source–sink balances.

The STICS model is organized into informatics “modules,” each of which corresponds to a set of ecophysiological processes (phenological development, leaf growth, radiation interception and photosynthesis, yield and quality formation, root growth, water balance, soil nitrogen processes , microclimate, and heat, water and nitrate transfers).

The most strategic information is provided by the development module, because it drives crop growth by organizing, throughout the cycle, the opening and closing of sinks as well as sink strength.

The development module also acts on sources by controlling the establishment of the photosynthetically active system and activating remobilization to the storage organs.

The other information provided is “stress”-type information that is considered in STICS to be constraints on the potential functions of the cover.

For inputs, the model requires climate variables that characterize, for each day in the simulation, the state of the atmosphere in the vicinity of the system: radiation, temperature, rain, etc.

The model also simulates the effect of agricultural practices on the system and thus requires input information such as sowing date (which will in part determine plant emergence), fertilizer types and rates, and irrigation schedule.

Lastly, the permanent features of the system are essential for capturing the specific ecophysiology of the crop under consideration (such as its potential radiation use efficiency) and soil properties (such as its moisture at the wilting point and at field capacity). In addition, the initial state of the system must be described, such as the water and nutrient contents in the soil or the initial state of the plant.

The outputs of STICS reflect the objectives of the model’s creation: outputs of agronomic interest such as the yield or quality of harvested organs (sugar content, oil content, etc.) and outputs appropriate for providing an environmental balance for the crop (amount of nitrate leaching, N₂O emissions, etc.).