Evaluation of the CropSyst Model during Wheat-Maize Rotations on the North China Plain for Identifying Soil...

The North China Plain (NCP) is a major grain production zone that plays a critical role in ensuring China's food supply. Irrigation is commonly used during grain production; however, the high annual water deficit [precipitation (P) minus evapotranspiration (ET)] in typical irrigated cropland does not support double cropping systems (such as maize and wheat) and this has resulted in the steep decline in the water table (~0.8 m year^-1 at the Luancheng station) that has taken place since the 1970s. The current study aimed to adapt and check the ability of the CropSyst model (Suite-4) to simulate actual evapotranspiration (ET_a), biomass, and grain yield, and to identify major evaporation (E) losses from winter wheat (WW) and summer maize (SM) rotations. Field experiments were conducted at the Luancheng Agro-ecosystem station, NCP, in 2010-2011 to 2012-2013. The CropSyst model was calibrated on wheat/maize (from weekly leaf area/biomass data available for 2012-2013) and validated onto measured ET_a, biomass, and grain yield at the experimental station from 2010-2011 to 2011-2012, by using model calibration parameters. The revalidation was performed with the ET_a, biomass, grain yield, and simulated ET_a partition for 2008-2009 WW [ET_a partition was measured by the Micro-lysimeter (MLM) and isotopes approach available for this year]. For the WW crop, E was 30% of total ET_a; but from 2010-11 to 2013, the annual average E was ~40% of ET_a for the WW and SM rotation. Furthermore, the WW and SM rotation from 2010-2011 to 2012-2013 was divided into three growth periods; (i) pre-sowing irrigation (PSI; sowing at field capacity) to emergence period (EP), (ii) EP to canopy cover period (CC) and (iii) CC to harvesting period (HP), and E from each growth period was ~10, 60, and 30%, respectively. In general, error statistics such as RMSE, Willmott's d, and NRMSE in the model evaluation for wheat ET_a (maize ET_a) were 38.3 mm, 0.81, and 9.24% (31.74 mm, 0.73, and 11.89%); for wheat biomass (maize biomass) they were 1.25 Mg ha^-1, 0.83, and 9.64% (0.78 Mg ha^-1, 0.96, and 7.96%); and for wheat grain yield (maize grain yield) they were 0.65 Mg ha^-1, 0.82, and 9.87% (0.2 Mg ha^-1, 0.99, and 3.79%). The results showed that CropSyst is a valid model that can be use with a reliable degree of accuracy for optimizing WW and SM grain yield production and water requirement on the NCP.