A dual degree course is sometimes beneficial than a simple B.Tech course because it can save a year of yours. A simple B.Tech degree taken 4 years,  and a M.tech takes 2 years,  but a dual degree B. Tech + M. Tech course takes only 5 years.
So,  I would suggest you to go for a dual degree course.

Hope I am clear.

Hii Ravi, 

I understand your situation I have myself been into this situation. So I will suggest you to go for simple Btech course if you have to settle soon in your life. 

If you want to study more, explore more and raise your academic standards go for mtech dual degree. Btech agriculture now totally depends on your interests like do you like this field, will you be comfortable will it and especially job opportunities. 

So yes I cleared you the fields the final choice depends on you. 

All the best for your future endeavors