Although there is a linear relationship between conductivity and and SAR backscatter, you would have to remove all other contributions to the signal.
If you had two absolute identical areas (same soil type, same roughness, same vegetation cover,…) and one had a higher conductivity than the others you would see a difference in backscatter intensity between them. But as no area is like the other and SAR data additionally contains speckle, you can never know if the backscatter variation results from moisture, roughness, vegetation by looking at the image.
It is good to collect field data on conductivity, so you can relate your measurements to the pixel values, but this will require a well-designed systematic data collection over multiple dates to reduce the impact variations of the other contributing factors (roughness). If there is vegetation in your study area, this is almost impossible, because the backscatter is not coming from the ground but from the leaves and branches.
I see many similarities to the retrieval of soil moisture which has the same challenge: You might want to have a look at these topics, especially johngan’s comments:
