Foliarly Applied 24-Epibrassinolide Modulates the Electrical Conductivity of the Saturated Rhizospheric Soil Extracts of Soybean under Salinity Stress

The accumulation of salts within the rhizosphere is a common phenomenon in arid and semi-arid regions where irrigation water is high in salts. A previous study established the ameliorative effect of foliarly applied 24-epibrassinolide (BR) on soybean under salinity stress. As a follow-up to that study, this work evaluated the effects of BR on the electrical conductivity of saturated soil extracts (ECses) under soybean exposed to salt stress. Three salinity levels (3.24, 6.06 and 8.63 dS/m) in a factorial combination with six frequencies of BR application—control, seedling, flowering, podding, seedling + flowering and seedling + flowering + podding—were the treatments, and the rhizospheric ECse was monitored from 3 to 10 weeks after the commencement of irrigation with saline water (WAST). The principal component analysis revealed that samples in saline BR treatments clustered together based on the BR application frequencies. There was a significant increase in ECse with increases in salinity and WAST. The frequent application of BR significantly reduced ECse to 5.07 and 4.83 dS/m relative to the control with 6.91 dS/m, respectively, at week 10. At 8.63 dS/m, the application of BR (seedling + flowering + podding) reduced ECse by 31.96% compared with the control. The underlining mechanism is a subject for further investigation.