It does look like a nutrient deficiency. I used to know what it was by the look of those leaves, but I've forgotten. (Been over 29 years since I've had that problem).

I wouldn't be too worried as long as the plants are growing and producing. But I would consider side dressing with a good compost. It's easier to prevent the problem than to fix it, in my opinion. Simply make and use compost. This will buffer the soil and enable the plants to use available nutrients.

George
Tahlequah, OK