Earlier sowing combined with nitrogen fertilization to adapt to climate change effects on yield of winter wheat in arid environments: Results from a field and modeling study

Climate change effects on crop production are of high concern in arid regions that are suffering from increased drought. We parameterized the APSIM-Wheat (The Agricultural Production Systems sIMulator) model using data of two field experiments conducted in 2017 at two locations (Karaj and Khomein) in Iran differing in temperature and precipitation. The experiment was a split plot with four replications. Main plots measured 17 m by 5 m with four irrigation regimes of full irrigation (I-1), deficit irrigation from grain filling (I-2,), from beginning of flowering (I-2), and during the whole growth period (I-4). Sub-plots measured 3 m by 5 m with nitrogen (N) levels of 200 (N-1), 100 (N-2) and 50 (N-3) kg/ha of urea (46 % N). N-1 resulted in highest wheat biomass, grain yield, harvesting index and leaf area index (LAI), with the differences between the N levels decreasing with increasing water deficit period. The model was parameterized for both localities with data of treatment I-1 +N-1, then evaluated over 11 combinations of irrigation and nitrogen rates. Root mean square of errors (RMSE) were 0.3 and 0.15 t/ha for wheat biomass and grain yield, and 3.54 days for wheat phenology and 0.28 for LAI simulations. After model calibration, we ran the model with 20 general circulation models (GCMs) under two representative concentration pathways (RCP 4.5 and RCP 8.5), and crop production was projected for three future time periods. For 2010-2039, models simulate a marginal increase in wheat yield, however, with 2040-2069 and 2070-2099, most models simulate a decreased growing season length and grain yield. Nitrogen application was found to decrease the drought impact. Additionally, model simulation suggests that earlier sowing time and excessive irrigation are of benefit in adapting to climate change impact. Thus, in arid environments where additional irrigation is not an option, increased nitrogen application in combination with an earlier sowing time could be an effective adaptation strategy for future wheat production.