That isn't N deficiency, it affects the lower leaves first. I think it is a micro nutrient deficiency, and I think it is Zinc but I wouldn't swear to it. Regardless, you are far enough along that you could have been feeding some time ago. Make sure your ph in the soil is proper, like 6.5-6.8 and give her a good dose of nutrients. Do you have micro nutrients as well? If not, check the back of your nutrient bottles and see if any contain chelated zinc. If so, see if they give instructions on foliar feeding. That will get the nutrients to the plant the quickest. Don't foliar feed only, also feed the soil but do both. Shoot me a pm if you need any more help and I will come back to your thread.