Got 2 questions: I have some cukes (one vine each in 5 gallon containers), they began very well dark green but since faded to lighter green and lower yellowing of leaves. See pics. It's hard to tell, but the cuke leaves on the left is quite darker than the right. They get lighter by the day. There are yellow specs on the leaves, more pronounced lower on the stem.

I have tomatoes in larger 18 gal (Watermelon beefsteak, Lg Italian plums). Those are also yellowing on lower leaves, some in middle.

Is this a deficiency?
Am I watering too much, too little? Using 1/4 in .5 gallon/ hr emitter irrigation system (cukes have 3 emitters each) with 25 PSI regulator and run for 15 min/ day. Soil seems moist but not wet. The tomatoes have 4-5 emitters per container.