soughi habiballah

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.

Determining the exact sowing date is an appropriate tool in controlling the length of the phenological stages for optimizing the climate conditions and minimizing the effects of terminal heat and drought stresses. The agro-climatic indices are used to study of plant phenology and its relationship with grain yield. Agro-climatic indices are changed under climate change conditions. The response of crops to climatic conditions can be assessed at the plant phenological stages by monitoring these indices. The aim of this study was to investigate the grain yield of new wheat cultivars related to northern warm and humid agro-climatic zone (Iran) under different sowing dates based on agro-climatic indices in Gonbad area.

This experiment was conducted in Gonbad agricultural research station, Gonbad, Iran, during two cropping seasons (2017-2019) as split plot based on randomized complete block design (RCBD) with four replications. Five sowing dates of 1 November, 16 November, 1 December, 16 December and 31 December were placed in main plots and four spring wheat cultivars including Ehsan, Tirgan, Meraj and Kalateh were placed as subplots. In each phenological stage, agro-climatic indices were calculated which includes total day length (DL), photoperiod (PPD), growth day degree (GDD), photo-thermal unit (PTU), helio-thermal unit (HTU), hydro-thermal unit (HYTU), heat use efficiency (HUE), helio-thermal use efficiency (HTUE), photo-thermal use efficiency (PTUE) and hydro-thermal use efficiency (HYTUE).

The results showed that no significant differences were observed in grain yield of second (25 November) and third (10 December) sowing dates (5708.3 and 5626.4 kg ha-1, respectively) and their grain yield was significantly greater than other sowing dates. The grian filling period, number of spike per square meter and number of grain per spike were not significantly different in three primary sowing dates. The third sowing date had the highest values in terms of agro-climatic indices including growing degree days (GDD), day length (DL), photo-thermal units (PTU), hydro-thermal units (HYTU), during grain filling period. While, the second sowing date had maximum heat use efficiency (HUE), helio-thermal use efficiency (HTUE), photo-thermal use efficiency (PTUE) and hydro-thermal use efficiency (HYTUE). Grain yield (5269.8 kg ha-1) and number of spike per square meter (330.17) of Kalateh cultivar were significantly greater than other cultivars (Tirgan, Meraj and Ehsan).

The second and third sowing dates provided suitable conditions for plant height and resistance to lodging in different cultivars. Also, the two mentioned sowing dates were provided optimum conditions for different cultivars in terms of climatic parameters including temperature, day length, relative humidity and energy use efficiency, during grain filling period. The grain yield decreased due to severe plant lodging in the first sowing date and exposure to terminal heat and drought stresses and reduced the grain filling period duration in the fourth and fifth sowing dates. The growth period of Kalateh cultivar was shorter than other cultivars (no difference during grain filling period), which caused the plant to escape terminal heat and drought stresses, increasing energy use efficiency and consequently increasing grain yield compared to other cultivars. Therefore, Kalateh cultivar is very suitable and advisable for cultivation in low rainfall areas in northern Golestan province in the second and third sowing dates.