Yellow leaves

I am growing outdoors and have been getting yellow leaves on one of the plants. Have checked the Ph levels and they are good. There is probably 5% of the leaves that have this issue. Does anyone have any ideas what may be causing this?

are these lower leaves ?

yes, but i need more info to be sure. but if the plant is losing its lower leaves, it needs nitrogen.

here these pics will probably help, your plant is probably looking like the plant in pic #1 (aka: N deficiency early stage)

Yes, the leaves are on the bottom. There is still new green leaves growing, and there are a few pale green-yellow leaves. It's Chem Dawg about 13 weeks in the ground.

It's hard say without a pic!
And a few questions~what you growing in, what dirt or wherever your using, what feed'em?