That's not just Nitrogen fade, it starts at the base and center and moves outwards to the tips. That's sulfur deficiency, which is completely normal if you're near the end of flower, but if you're all organic and want to take care of it, some worm castings top dressed andn water in well should take care of it, or a worm castings tea brew watering, which either wont affect taste or anything at harvest. Sulfur is an important element for growth.