What are you feeding? How much?
If you think it's N def, fish emulsion is good for the soil.
The first picture, the leaves closest to the camera (at the bottom of the pictue) look kind of glossy, buckled and blistered? That makes me think overfeeding, which could cause lockout and n-def. The other leaves don't look like that, however.
The new growth, I see some dark spots (in the last two photos). Is that shadows, or dark spots?