Dear Radha,
It is true that SAR data can be used for agricultural modelling and related goals. And yet I am afraid that we do not have a specific process for agricultural mapping or yield estimation that we can outline for you. I am told that we will have a webinar coming up soon (not yet scheduled) that will discuss some issues around agricultural monitoring, among other topics. Perhaps that webinar will be helpful for you.
There is a brief discussion of using SAR data for agricultural monitoring in the SAR Guidebook available from
http://www.sarmap.ch/pdf/SAR-Guidebook.pdf. Look for section 3.1.
Best,
Peg Shippert