Too many people go out of their way to cut out N while in flower when the plant still needs N in flower. Without nitrogen the plant can't produce chlorophyll which is required for the process of photosynthesis to occur. It also is used for nutrient uptake and believe it or not is used in the production of flowers. The fade with yellow leaves at harvest that some people think is is normal is actually a plant that has been starved of what it needs to reach maximum yield.