If I study agriculture from a non ICAR university but the university is UGC approved will I get a govt job of agriculture?

Both ICAR and UGC are two different organizations and both have different roles. UGC plays an important role in traditional education while ICAR plays an important role in agricultural education. 

You can get a government job based on the requirements for that job. If they demand a graduate from any college or university without any special mention for an ICAR affiliated university, then you will be eligible for that job. But if it is clearly mentioned ICAR affiliated universities only, then you won't be able to apply for that job. 

Choosing an ICAR affiliated college will be a better option as it focuses on agriculture specially and it will create new possibilities of getting a better government job and getting more recognition and fame in this field.