Introduction
Silicon is increasingly recognized as a beneficial element for improving plant growth by enhancing physiological, biochemical, and molecular responses. It plays a role in various plant processes like osmosis, metabolism, stomatal physiology, and phytohormone relationships. Some researchers believe that silicon, as a signaling molecule, reduces damage caused by reactive oxygen species and ionic leakage by increasing the plant's antioxidant defense capacity. silicon plays a significant role in increasing the accumulation of photosynthetic materials in seeds; researchers attribute this increase to the flow of assimilates towards the seed, reduced source limitation, enhanced sink capacity, and improved remobilization of photosynthetic materials. The results indicate that silicon can affect the production and allocation of dry matter and the relationship between source strength and sink size. The consumption of silicon leads to favorable interactions with fertilizer elements such as potassium, thereby enhancing agronomic traits and improving the efficiency of this element to increase yield. Potassium plays a crucial role in osmotic control, enzyme activity, regulating cell pH, maintaining the balance between anions and cations within cells, controlling evaporation and transpiration through stomatal regulation, and aiding in the transport of metabolic materials from photosynthetic activities, ultimately improving yield by increasing leaf area and chlorophyll content. It has been shown that the application of silicon improves biomass, seed yield, and tiller number in several crops. Bitter vetch is a forage plant from the legume family and is native to regions in West and Southwest Asia, cultivated in various countries, including Iran. Bitter vetch is ecologically adaptable to drought and has always been of interest due to its high nutritional value, short growing period, and ability to fix soil nitrogen. The research aims to investigate the effect of silicon as a signaling molecule in nutrient remobilization in bitter vetch to enhance yield.
 
Materials and Methods
In order to investigate the effect of potassium silicate levels (control (distill water), 2/1000, 3/1000, 4/1000 and 5/1000) on bitter vetch plant yield, an experiment was conducted in the form of a randomized complete block design with three replications at the Faculty of Agriculture, Ferdowsi University of Mashhad, Iran. In this study, local seeds from Lorestan province were used. The seeds were manually planted at a depth of two centimeters in the soil in the first half of February 2022. The application of potassium silicate was carried out in two stages as foliar spraying. The first stage took place at the time of pod formation and 10 days after first application. At the end of the growth season, morphological traits including plant height, lowest pod hight, number of secondary branches in five plants, 1000- grain weight and yield traits were were measured and recorded. Statistical analysis was performed using the LSD method.
 
Results and Discussion
The application of potassium silicate significantly affected plant height, leaf canopy height, number of secondary branches, seed weight, seed yield, biomass, and harvest index. Silicon plays a role in strengthening the cell walls of stems and leaves, enhancing their physical strength, which can improve plant growth and light absorption by leaves, thereby stimulating plant growth. The results showed that the highest grain yield and biological yield in the foliar spraying treatment were 5/1000 and 4/1000 potassium silicate, which increased by 28 and 44%, respectively, compared to the control. In addition, the highest plant height, the number of branches and the weight of 1000- grain weight were observed in treatment of 5/1000 potassium silicate. The results showed that grain yield has a positive and significant correlation with the number of sub-branches (r = 0.51^**), 1000- grain weight (r = 0.65^**) and biological yield (r = 0.46^**), respectively. In the present experiment, the positive and significant correlation of seed yield with the weight of 1000- grain weight and biomass shows that the process of transferring and distributing photosynthetic products to the reservoir is directly related to the source. The application of potassium silicate had a positive impact on various physiological processes, leading to increased biomass production and ultimately enhancing seed yield.
 
Conclusion
The application of potassium silicate significantly increased seed yield and had positive effects on various yield components of bitter vetch plants. Silicon application during the formation of sheath and sheath development enhances the translocation of photosynthetic materials to reproductive organs, ultimately improving plant performance.