How well does APSIM NextGen simulate wheat yields across Australia using gridded input data? Validating Continental-Scale Crop Model Simulations

Processed-based models are increasingly being used with gridded soil and weather data; however, their validation is often on small, sampled datasets, calling into question their accuracy when extrapolated to larger scales with more uncertain input data. Here, we benchmarked the accuracy of the APSIM Next Generation (APSIM-NG) crop model for wheat yield predictions on multiple trials from 2005 to 2022 using data from the largest independently coordinated national trial network in the world (Australia’s Grain Research and Development Corporation’s National Variety Trials). This gauged the validity of APSIM application with gridded soil and weather data across the 60 million ha of the Australian grain belt over time. Overall, results indicated that APSIM-NG can track the spatial-temporal changes in wheat yields from the studied period at the national, state, or agroecological level – nationally: R2 = 0.5, d = 0.83, a bias of 6.9%, non-significant monotonic trend (p>0.05), and significant Genetic X Environment effect (p