Agronomic and Physiological Characteristics of Forage Sorghum (Sorghum bicolor L.) under Water Deficit Stress and Silicon Fertilizer

The quantity and quality of forage plants are beneficial and useful due to their role in animal husbandry, reproduction and other livestock products. Due to the limitation of water resources, water-deficit as a significant biotic stress is the most severe threat to world food security and is responsible for many yield losses. Plants constantly modify their physiological processes in response to various biotic and abiotic stress to regulate the balance between plant growth and defense response. Many researchers have documented that plant nutrients are involved in biological processes of plants. It has been stated that the use of silicon by increasing the ability to absorb water can be useful to improve drought tolerance of sorghum, sorghum can with the help of silicon extract more water from dry soil and maintain more stomatal conductance.

order to evaluate the effect of silicon fertilizer on the quantitative and qualitative yield of forage sorghum (Sorghum bicolor L.) under water-deficit stress, a split-plot experiment was performed in a randomized complete block design in at the research farm of Varamin, Iran in 2017-2018. The treatments included irrigation in three levels irrigation in field capacity and irrigation at 60% and 45% of field capacity (which were named as full irrigation, moderate and severe water-deficit stress, respectively) as the main plot and silicon fertilizer (Potassium Silicate) in three levels, non-use (control), silicon foliar spraying (three per thousand), and silicon fertigation (10 L ha-1) as the subplot. Silicon spraying with a ratio of three per thousand and silicon irrigation fertilizer at the rate of 10 liters per hectare were considered in three stages.

The highest (4.51) and lowest (2.88) leaf area index were achieved in silicon fertigation treatment under full irrigation and none fertilizer treatment and severe water-deficit conditions, respectively. Based on the obtained results, the highest total chlorophyll content (1.73 mg g-1 FW), relative water content of leave (88.08%), stomatal conductance (2.46 cm s-1) were achieved in fertigation treatment under full irrigation conditions. The results show that the amount of electrolyte leakage increased due to water-deficit stress, but silicon fertilizer decreased the adverse effect of stress conditions. The lowest level of electrolyte leakage (341.3 µS cm-1) was obtained from the full irrigation and fertigation treatment. The highest crude protein (11.41%) which was higher than full irrigation condition by 1.39% related to severe water-deficit stress. Water-deficit stress caused the increase of cyanuric acid in shoot and increased the content of cyanuric acid by 41.8% compared to full irrigation conditions. Silicon fertilizer led to a decrease in digestible dry matter under water stress conditions, but on the other hand, it led to an increase in the amount of crude protein and also a decrease in the amount of toxic cyanide acid in the shoot production. The results of this study show that the use of silicon fertilizer in all irrigation regimes increased the auxin content compared to the non-use of silicon fertilizer. The highest content of auxin was achieved in the conditions of full irrigation and fertigation treatment (131.4 nmol g-1 of protein) followed by foliar fertilizer treatment (128.2 nmol g-1 of protein). The highest sorghum dry matter production was obtained from the full irrigation treatment with an average of 23.7 ton ha-1, which was 20 and 54% higher than the treatment of moderate and severe water-deficit treatment, respectively.

general, it can be concluded that silicon fertilizer in the form of foliar spraying should be considered by farmers to maintain the natural growth and development of sorghum plant, especially in areas arid and semi-arid. However, its widespread use in other farm crops needs to be investigated.