Young plants - Turning Yellow

Hey everyone, was wondering if I could get some help. I had a successful grow last year. Using same method. This time I have 3 plants instead of one.
These new ones are turning yellow on bottom leaves. Nitrogen deficiency? The last two plants I had started this year did the same thing.
I got new soil this time and its still happening. I have not started using my nutrience yet. Just using water and sun light. These are outdoor plants.
The nutrience I use for vegetative stage is stagreen boost packs 24-8-16. Did well last year but I waited a little while to use. Thanks for any advice to keep these things a live. Appreciate it!
 

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