Wow....that's a BIG plant! Can you provide any further details on your grow? What kind of lighting, how many watts, what have you been feeding so far, are you using soil, etc.
You'll find a bit more help with a little more info! I'm just going into flowering for the first time with my plants, but I'd imagine you want to feed your plants a balanced fertilizer that actually contains enough nitrogen to keep your leaves as healthy and green as possible until harvest time approaches. Buds feed from the leaves to get bigger so if they are yellowing and dying off, that means less photosynthesis for flowering and thus lower yield! High phosphorus fertilizers are actually more marketing hype than they are helpful to get you large yields; and from what I understand too much phosphorus actually hinders flowering and causes most deficiencies that are common in flowering.
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