Good pics... real simple... early N def & associated die back of lower leaves where they are probably not getting much light as well, though the latter not definite. You can also see some purple starting to come into the stems/leaves, which will be your P or K kicking in. The yellowing & die back of lower leaves is just lack of N. Best brah.

EDIT- in other words, they are hungry... no nutes in 38 days = time to feed a light soil solution.

EDIT, EDIT- "...which will be your P or K [deficiency] kicking in." ) Peace!