Quoted from: https://www.apsim.info/apsim-model/

The Agricultural Production Systems sIMulator (APSIM) is a comprehensive model developed to simulate biophysical processes in agricultural systems, particularly as it relates to the economic and ecological outcomes of management practices in the face of climate risk. It is also being used to explore options and solutions for the food security, climate change adaptation and mitigation and carbon trading problem domains. From its inception twenty years ago, APSIM has evolved into a framework containing many of the key models required to explore changes in agricultural landscapes with capability ranging from simulation of gene expression through to multi-field farms and beyond.

APSIM is structured around plant, soil and management modules. These modules include a diverse range of crops, pastures and trees, soil processes including water balance, N and P transformations, soil pH, erosion and a full range of management controls. APSIM resulted from a need for tools that provided accurate predictions of crop production in relation to climate, genotype, soil and management factor while addressing the long-term resource management issues.

The APSIM modelling framework is made up of the following components:

• A set of biophysical modules that simulate biological and physical processes in farming systems.
• A set of management modules that allow the user to specify the intended management rules that characterise the scenario being simulated and that control the simulation.
• Various modules to facilitate data input and output to and from the simulation.
• A simulation engine that drives the simulation process and facilitates communication between the independent modules.

In addition to the science and infrastructure elements of the APSIM simulator, the framework also includes:

• Various user interfaces for model construction, testing and application
• Various interfaces and association database tools for visualisation and further analysis of output.
• Various model development, testing and documentation tools.
• A web based user and developer support facility that provides documentation, distribution and defect/change request tracking.

A description of Crop Growth and Development Framework in APSIM Crop Models can be foundhere.

A list of models in release can be found here.

For more information and citation references, please refer to:  APSIM citation

To access APSIM 7:10 documentation, please refer to: APSIM 7:10 

To access APSIM Next Generation documentation, please refer to APSIM Next Gen