Yellowing and browning leaves - what is wrong/ how do I fix it?

I am a beginner grower. I have Northern Lights and Indica mix pack seeds from ILGM.

A few days ago a few of my plants, not all of them, began looking unhealthy, with yellow leaves at the bottom, then edges turning brown. So far the top of the plant still looks ok.

Located in Virginia, we’re growing outdoors. Plants are about 30 days old ,6 inches high and I transplanted them into larger 1/2 gallon pots last week.

PH of soil in healthy plants is around 7.5, PH of soil in unhealthy plants closer to 6.5. Moisture levels seem ok (“moist” reading). The soil itself is a mix of potting soil, peat moss and river bank soil which I use for my vegetable garden (and things really grow well in it!). I am using Jobes organic granule plant fertilizer with NPK of 2-5-3.

I know I need to transfer to 5 gallon pots soon but would like to better understand what is going on with the yellow/brown leaves at the bottom / mid of the plant before I do.

I suspect nitrogen deficiency. Please advise!!!

Hey welcome,looks like a nitrogen or some other deficiency for sure but more experienced guys like@mrpeat or @ blackthumbbetty would know.Tag a more experienced grower that you see on the forum.