Simulation of Yield and Water Productivity in New Bread Wheat Cultivars Using DSSAT-Nwheat Model

Crop simulation models are widely used in the analysis of cropping systems, climate change and crop management methods. It is a good tool for completing and developing the results of field trials to evaluate new cultivars and new management systems. The aim of this research was to simulate the phenological stages and yield of different bread wheat cultivars in climatic conditions of Gorgan city using DSSAT-Nwheat model.

In this study, in order to evaluate the performance of the DSSAT-Nwheat model, the data drived from a two-year experiment (Growing seasons 2019-2020 and 2021-2020), in which four new bread wheat cultivars were studied under seven sowing dates as split plot based on randomized complete block design (RCBD). Seven sowing dates (from 1 November to 31 December, 10-day intervals) were placed in main plots and four bread wheat genotypes (including Arman, Araz, Taktaz and N-93-9) were placed as subplots. The data derived from the first year and the second year were used for calibration and validation of the model, respectively. In addition to field data, daily meteorological data, management events, soil characteristics and geographical coordinates were provided to DSSAT 4.7 software. After determining the genetic coefficients of each genotype, the model was calibrated for different traits and subsequently the same coefficients were used to validate the model. Using statistical indices, the simulated values of the model were tested with the observed values.

The results showed that the phenological stages including day to anthesis and day to maturity were simulated with root mean squared error (RMSE) equal to four days, and normalized root mean square error (nRMSE) less than 3%. RMSE for grain yield and biological yield were 416 kg ha-1 and 1000 kg ha-1, respectively, and nRMSE values were between 7-8%. In water productivity based on grain yield and biological yield, nRMSE values were 6.21% and 7.53%, respectively, and RMSE values were 0.93 kg ha-1 mm-1 and 2.91 kg ha-1 mm-1, respectively. In all the simulated traits, the Willmott's agreement indices (d) and the coefficient of determination (R2) were in the acceptable range, which showed the proper performance of the DSSAT-Nwheat model for simulating these traits in different bread wheat cultivars.

The results of this study showed that the DSSAT-Nwheat model had proper performance for simulating phenological stages, grain yield, biological yield and water productivity in four cultivars including Araz, Arman, Taktaz and N-93-9. The nRMSE values for all studied traits were between 6-8%. The cultivars studied in this study are the latest cultivars released for the northern warm and humid agro-climatic zone, Iran, in the next few years, they will occupy a large area of wheat cultivation in Golestan province. Therefore, it seems that the results of this study can be used in the decisions of wheat cultivation systems, different effects of agricultural management and current and future climate change in Golestan province.