Straw Bale Gardening

[Mrs. Crappie Stalker]

Six weeks in. Plants are doing pretty well. I've had some yellowing of the lower leaves. I know this can happen from overwatering, but are there other causes as well? It has only been on the tomato, pepper and okra plants. The beans, cukes and squash don't have that problem. I have some baby peppers and tomatoes and all of have blooms.