Automatic agricultural robot using 8051
What you need, friend is simply a proof of concept.

Step 1- Put down the 8051 and forget about it - go get an off the shelf arduino. You will run out of time building it in and debugging it. Only go back to it if your professor insists that arduino is too easy.

Step 2 - Go build the arduino into a rolling platform. This has been done so many ways, you'll have an easy time finding one - maybe even in a kit. 

Step 3 - Add an off the shelf GSM shield  kit, put in a reliable prepaid sim card, and start debugging that. 

Step 4 - Add LEDs to whatever digital pins you have left. Write code into your controller that makes them flash at defined points in the run. Call it the "fertilizer function". 

Step 5 - Present the heck out of it. Make the presentation a sales pitch and exude confidence. Be able to answer all the questions intelligently - this is more important than actually making the thing turn circles and light up.

Step 6 (optional) - Get serious about this idea, follow up on all the loose ends, find investors and build it until someone buys you out.