Simulation of Sugar Beet (Beta vulgaris L.) Root Yield and Water Productivity in Response to Different Sowing Date and Irrigation Treatments using SUCROS Model

 Water is considered as one of the main factor driving agricultural activities. It is predicted more than 67% of the world's population will suffer from water shortages in their habitats that by 2050. Therefore, maximizing water efficiency is the best solution to deal with the problem. Water productivity is an important factor in evaluating the efficiency of irrigated and rainfed systems. Sugar beet is one of the strategic crops in Iran which its area under cultivation has been decreased in the last two decades, especially in Khorasan Razavi Province. The high water requirement of sugar beet and the problem of water shortage during spring and summer are the most important reasons for the decrease in the area under cultivation of this crop. Given the crisis in water supply for crop production, increasing water productivity in irrigated agroecosystems can be considered as a suitable strategy to increase the area under cultivation and yield of crops. In recent years, different studies have been conducted to increase the water productivity of different crops using simulation models.

 In this study, root yield and water productivity of sugar beet were evaluated in response to three different sowing date treatments (20 February, 21 March, and 21 April) and four irrigation interval treatments (10 days, 12 days, 14 days and treatment with model according to the crop water demand) in Neyshabur, Sabzevar, Quchan, and Torbat Jam locations. For this purpose, the SUCROS simulation model and long-term meteorological data were used to estimate the growth and production of sugar beet. In addition, the trend of sugar beet daily water demand as well as changes in soil water in different treatments during the growing season was extracted and analyzed.

 The results showed that the highest yield of sugar beet (63.80 t ha-1) was obtained in Sabzevar by sowing on 20 February and irrigation with 10 days intervals while in Torbat Jam, Neyshabur, and Quchan, the maximum root yield (66.44, 109.38 and 112.15 t ha-1, respectively) was achieved by sowing on 20 February and irrigation based on crop water demand.  In contrast, sowing sugar beet on 21 April with 14 days of irrigation intervals in all studied locations resulted in the lowest yield among different treatments. Water productivity comparison in different locations showed that in Sabzevar, Torbat Jam, and Neyshabur, the treatment of the 20 February sowing date and irrigation based on crop water demand resulted in maximum water productivity (4.08, 4.52, and 8.10 kg m-3, respectively) and in Quchan, the treatment of 20 February sowing date and 14 days irrigation interval with 7.70 kg m-3 led to the maximum water productivity. The results also indicated that in Sabzevar, the lowest water productivity was obtained by sowing sugar beet on 21 April and irrigation with 14 days intervals, and in Torbat Jam, Neyshabur and Quchan, the minimum water productivity was simulated by sowing date of 21 April and 10 days irrigation intervals. Evaluation of the relationship between the length of growth season (as a criterion of sowing date) with sugar beet yield and water productivity in all locations showed that there were significant relationships among these variables and the length of growth season at 1% of probability level, which indicated the importance of early cultivation in increasing the sugar beet production and water productivity in Razavi Khorasan Province.

The findings of this study suggest that modifying the sowing date, in comparison to adjusting irrigation intervals, may have a more significant impact on enhancing sugar beet yield and water productivity. Additionally, in warmer locations like Sabzevar and Torbat Jam, exploring alternative options such as autumn sugar beet cultivation is advisable. In light of the constraints posed by limited water resources, it is recommended that researchers prioritize investigations into water productivity rather than solely focusing on maximizing crop yield.

Acknowledgments:

The authors are grateful to Dr. Reza Deihimfard from Shahid Beheshti University, Iran for providing valuable comments and his advice on methodology.