To study the effect of irrigation, plant density and salicylic acid on yield and yield components of Guar (Cyamopsis tetragonoloba L.)

The increasing use of medicinal plants and their products has elevated the importance of these plants in the global economy. The global consumption of these plants is rising rapidly. The guar plant (Cyamopsis tetragonoloba) is an annual herbaceous and medicinal plant. This plant is suitable for arid and semiarid climates, including Iran, due to its short life cycle. This plant's extracts are used in the cosmetics and health industries to create moisturizing creams. In addition, this plant's products are utilized in the medical, food, and petrochemical industries. In Iran's arid and semiarid regions, the optimal use of water in the production of agricultural and pharmaceutical products is one of the foremost concerns of researchers. In Iran's arid and semiarid regions, the optimal use of water in the production of agricultural and pharmaceutical products is one of the foremost concerns of researchers. Utilizing compounds that reduce the effects of stress, such as salicylic acid, is one of the suitable agricultural practices during drought conditions. In these conditions, it is also advised to plant at a suitable density for optimal use of light and other resources, and to avoid interplant competition. This research was conducted to determine the impact of irrigation and salicylic acid at various densities on guar yield and some of its characteristics.

In order to investigate the effect of irrigation, plant density, and salicylic acid on guar, an experiment was conducted in 2018 in Mashhad as a factorial split plot in a randomized complete block design with three replications. The main plot consisted of irrigation levels (25, 50, 75, and 100% evapotranspiration of the reference plant), while the sub-plot consisted of factorial levels of density (4.4, 6.7, and 13.3 plants per square meter) and salicylic acid (non-application and application).

The comparison of means revealed that the application of salicylic acid resulted in a 6.9% increase in plant height. Salicylic acid regulates various physiological processes, such as plant growth and development, through the synthesis of special proteins called protein kinase, which regulates cell division, differentiation, and morphogenesis, and has a significant impact on plant height. The full irrigation treatment produced the highest leaf area index (6.1) and plant density per square meter (13.3) compared to all other treatments. Under conditions of water stress, the decrease in photosynthetic capacity of the plant due to stomatal closure and the decrease in cell turgor and cell division cause the plant to have small and underdeveloped leaves, resulting in a decrease in the leaf area index in the field. Results indicated that providing 100% of the reference plant's evapotranspiration resulted in the highest average grain yield of 937.28 kg ha-1. By decreasing plant density at 100 and 75% of the reference plant's evapotranspiration, seed production in pods increased significantly, whereas increasing plant density decreased grain yield. The highest number of pods per plant, number of pods per square meter, 1000-seed weight, and biological yield were obtained under conditions of providing 100% evapotranspiration and application of salicylic acid. Additionally,, poor irrigation practices in the absence of salicylic acid application decreased guar's biological yield.

Due to limited water resources, it is recommended that this plant receive irrigation equivalent to 75% of the evapotranspiration of the reference plant in Mashhad conditions. In addition, intensive cultivation of this plant is not advised due to the impact of high densities on reproductive processes. Due to the lack of effect of salicylic acid on grain yield, its use in this plant, is not recommended.