Q:

One more Riley Riddle

For mandatory exercise does my prefix stand
  Watch out for always in the grass I land
  My suffix able of anything it desires
  or to withstand pressure and times 

What am I?  
hint:  

 In the orchestrated land I lie
 Now it's time for some delicious pie

hint 2:

 Add a two-letter infix and for a bird you'll confuse me
 We are the Lights who say: ...?

A:

You are

 pecan

For mandatory exercise does my prefix stand

 PE (physical education)

Watch out for always in the grass I land

 Pecan nuts fall from the tree into the grass

My suffix able of anything it desires
or to withstand pressure and times 

 can / canned food

Hint: In the orchestrated land I lie
Now it's time for some delicious pie

 Pecan pie is a thing

Hint: Add a two-letter infix and for a bird you'll confuse me
We are the Lights who say: ...?

 Lights who say "Li!" -> Pe(li)can

