HELP!!! nute problem???

hey i got a very nice and for the most part super healthy expet for the very bottom leaves all ways turn a bright yellow the drie out and die, it happend very early so i nuted and that helped for a minute but the it came back could i be over nuting now and how much should i use

P.S. its the same plant as my avatar so you can tell the top is healthy

maybe there not getting enuf Nitrogen same thing happens to me with all my plants but it happens later when there like 1 month old

ya mine is like just over a month old

does any one else think its under N because it happend with my last nutes that were full of N and not a bunch of P and K but now my new stuff is 30 20 20.
N P K