What are the 12th cutoff marks required for TNAU Coimbatore?

Clearly, your cut-off depends upon the category you belong from, as is for most of the universities. Generally, a higher cutoff is essential for the main campus, i.e. CBE. 

Now, in case you are talking about B.Sc Agriculture in the main campus, then your marks should at least be above 198 (including biology, mathematics, chemistry, and physics), given that you belong from the general category.

However, TNAU has other courses like horticulture, bioinformatics, agriculture information technology, and others which require a lower cutoff in the range of 190. These courses are quite good, in case you want to pursue research later.