John I didn't even say that it was a lack of nitrogen, but that it is normal for the plant to draw out a lot of nitrogen during stretching before pre-flowering and in pre-flowering itself, and because of that the lower leaves turn yellow, and some of the larger ones around the edges, and that is normal, it has to happen.
Of course, she does not need nitrogen now in flowering, except in case, if a deficiency appears, then add a milder dose, but now what is important is to give her sufficient amounts of potassium and in the second half of flowering, a lot of phosphorus, because the plants then consume abnormal amounts of phosphorus.
I don't think it's a lack of potassium, if it is, it's easy to determine, the leaves will be yellow, similar to the lack of nitrogen, only not all the way and not whole, and the edges will be brown-golden in color...eltoto45 the easiest thing is to find a table with pictures of deficiencies and excess, and by that you can easily recognize what the plant lacks or what it has more of, after a while you won't even have to look at the pictures