Investigating the effect of different levels of dehydration stress on morphological characteristics, yield and yield components Soybean cultivars (Glycine max L.)

Introduction:
Soybean, with the practical name Glycine max L., is an annual plant with high economic value, which has about 20% oil and 40% protein among oilseeds in the world, and has the largest cultivated area (120 million hectares). (FAO, 2019). Water deficiency is one of the limiting factors for soybean growth (Aminifar et al., 2013). The most important stage in which soybean is affected by drought stress is the reproductive stage (Asmail Khani et al., 2011). One of the methods that can be used to expand the area under soybean cultivation in such conditions and save on irrigation water consumption is to use the low irrigation method and promote drought tolerant cultivars.
This research was conducted with the aim of investigating the effect of different levels of insufficient irrigation on the growth characteristics, yield and yield components of some soybean cultivars under the climatic conditions of Jiroft city, Kerman province as an arid and semi-arid region.
Materials and Methods:
In order to investigate the effect of different levels of drought stress on the morphological characteristics, yield and yield components of soybean cultivars in Jiroft region, this experiment was carried out in the form of split plots in the form of a randomized complete block design with 18 treatments and 3 replications per year. 2017-2018 and 2018-2019 crops (for two consecutive crop seasons) were implemented in Jiroft Agricultural Research Center. The main factor was lack of irrigation at three levels of 90, 70 and 50 percent of water requirement and the secondary factor was six soybean varieties including Sari, Sahar, 504 Dezful, Tekavar, Telar and Zan. The distance between the rows and between the bushes on the row was 50 and 5 cm, respectively, and the amount of seed used per hectare was 70 kg. In order to prevent water leakage, the distance between the main and secondary plots was considered to be three meters. Before data analysis, data normality test and Bartlett's test were performed and normal data were analyzed using SAS software (ver. 9.2) and F test was performed for the sources of said change based on mathematical expectation of mean square. (EMS) was carried out assuming the randomness of the effect of year and the repetition and constant of the effects of other factors .Then variance analysis of the data for two years was done separately and the averages were compared with the LSD test at the five percent probability level. Finally, shapes were drawn using Microsoft Excel software and tables were made using Microsoft Word software and compared with each other
Results and Discussion:
The results showed that the effect of year was not significant on the studied growth and yield characteristics (except for the number of leaves and seeds per plant). In contrast, drought stress caused a significant decrease in growth and yield characteristics. So that, severe drought caused a decrease of 21.31 and 68.08% in plant height and seed yield compared to the control. The results showed that cultivar 504 Dezful had the highest growth characteristics and seed yield under the conditions of 90% filed capacity. The highest seed oil yield (916.41 kg/ha), protein percentage (36.06 %) and protein yield (1351.53 kg/ha) were observed in 504 Dezful variety under normal condition (90% FC). Also, this cultivar was higher yield (1281.06 kg/ha) to other cultivars under drought stress treatment.
Conclusion:
In general, 504 Dezful and then Sahar were identified as the drought-tolerant cultivar which can be used as a management strategy to improve soybean yield in arid and semi-arid regions.
Keywords: Cultivar, Drought stress, Soybean, Seed yield, Deficit irrigation, Harvest index.

Reference:
Aminifar, C., G.R. Mohsen Abadi., M.H. Beiglooei. and H.A. Smizadeh. 2013. The effect of irrigation on yield, yield components and water efficiency T.215 soybean varieties. Journal of Irrigation and Water Engineering. 3 (11): 24-34 (In Persian with English Summary).
Asmail Khani behben, H., AS. Nkhzry Mqadm, and M.R. Dadash. 2011. The effects of irrigation and nitrogen application on grain yield and reproductive traits of soy road. Journal of Crop Sciences. 4 (14): 80-67.
FAO. 2019. The FAO statistical yearbook, Food and Agriculture Organization of the United Nations. available at: http://www.fao.org/faostat/en/#data