Evaluating the Agricultural Production Systems sIMulator (APSIM) wheat module for California

Context: Computer-based crop simulation models are important tools for agricultural research and management. The Agricultural Production Systems sIMulator (APSIM) is commonly used around the world, but has not been widely validated in North America.

Aims: The objective of this work was to evaluate the reliability of APSIM for simulating wheat production in California, and to identify future research needs, by using pre-existing data from state-wide variety trials.

Methods: Environmental and management data from three seasons of state-wide wheat variety trials, were used to parameterize the APSIM-Wheat module (version 7.10 r4220). Simulated yield and protein data were compared to and actual field data to test the reliability of the APSIM simulations.

Key results: The most reliable simulation of grain yield had a root mean square error of 1040 kg/ha and normalised root mean square error of 16 % relative to actual field data.

Conclusions: The accuracy of the simulations was comparable to other tests of the APSIM-Wheat module in environments where it has not been previously calibrated, but was too low to be considered reliable. The lack of reliability was due to the poor representation of local Californian wheat genotypes, as well as inaccuracy of management and environmental data.

Implications: APSIM could be a valuable tool for wheat research and management in California, but our work shows the current model is unreliable. Further research is needed to generate field data needed for model calibration.