The APSIM-Barley module simulates the growth and development of a barley crop in a daily time-step on an area basis (per square meter, not single plant). Barley growth and development in this module respond to weather (radiation, temperature), soil water and soil nitrogen. The barley module returns information on its soil water and nitrogen uptake to the soil water and nitrogen modules on a daily basis for reset of these systems. Information on crop cover is also provided to the water balance module for calculation of evaporation rates and runoff. Barley stover and root residues are ‘passed’ from barley to the surface residue and soil nitrogen modules respectively at harvest of the barley crop.

Approaches used in modelling crop processes balance the need for comprehensive description of the observed variation in crop performance over diverse production environments and the need to avoid reductionist approaches of ever-greater complexity with large numbers of parameters that are difficult to measure.