Hii Venkatesan!

I would say it's not a right choice. You have studied PCMB subject çombinations in class 12th. So, you need to mark the PCB option in ICAR AIEEA. I don't think opting agriculture in this case is possible. And, you have a disadvantage there. Agriculture is not as easy subject as it seems. You need to know and study agriculture syllabus differently then. So, it's better to go for physics though you find it tough, but atleast have idea of the subject. Whereas in Agriculture, you are completely clueless. This will not serve the purpose.

Hope you understand.

Good luck!