Identifying changes to key APSIM-wheat constants to sensibly simulate high temperature crop response in Pakistan

Wheat production is impacted by increasing temperature at key developmental stages, potentially leading towards crop failure or reduction in yields. Process based crop simulations models can be useful tools for developing adaptation options and strategies for managing high temperature conditions, but the models must firstly be well-tested. The main objective of this study was to test APSIM-wheat under a diverse range of experimental treatments for simulating crop response to high temperature conditions. The APSIM-wheat model was parameterised, calibrated and validated under a diverse range of treatments including multiple factors (4 N rates x 2 sowing dates x 2 agro-climates) in high temperature conditions. The model was unable to adequately simulate crop phenology and production until we modified what are currently key species-specific parameters, not varietal parameters (governing thermal time and leaf senescence) to improve model behaviour in high temperature conditions. The improved model simulated observed crop phenology (days to anthesis and physiological maturity) and production (biomass and grain yield) of our validation datasets with high R2, EF and low RMSEs, RSR values. Subsequently, the model was also able to simulate cropping system performance (a maize-wheat rotation with different N rates and sowing dates) markedly well within the bounds of observed experimental error. We believe this robust improvement and testing approach has made APSIM useful in simulating wheat crop response to high temperature conditions, and therefore for ongoing research into different agronomic management practices (notably crop response to N-rate and sowing date) under prevailing and future climate conditions, however, calls into question the arbitrary split between species and varietal parameters in APSIM-Wheat. The improved version of APSIM-wheat is now a suitable tool for scenario analyses under elevated temperatures (climate change) and subsequent investigations of wheat crop response to N and sowing date under these conditions.