Strange yellow bottom leaves. Pics included

So i am doing an outdoor grow. The strain i am growing is grape god and i am using botanicare pure blend pro (Foliage) Its 3-2-4. On 2 of my plants there are single completely yellow leaves at the bottom. I feed them nutes regularly and ph is in balance last time i checked. Is this yellowing normal or do i have a nitrogen issue?

pictures:http://imgur.com/a/o54IK

http://imgur.com/a/Q2zJW

http://imgur.com/a/imc8Y

Looks pretty normal to me...just keep an eye on it.

yeah pretty normal

Looks like a P or K deff but its just the bottom 2 on each plant sometimes the plant does that to grow more roots

Awesome thanks alot for the help. I will ad a small increase in fertilizer