Would this be a zinc or a sulfur deficiency?

[Bigdylan04]

Hello 2 questions, can someone tell me why my bottom leaves are yellowing ? And also the front right plants top leaves are a lighter green than the other plant can someone explain why? Thanks in advance

 

[HempKat]

Of the two choices I would tend to go more with zinc then sulfur because with a sulfur deficiency the veins are usually paler then the rest of the leaf but in your pictures your leaf veins appear darker then the rest of the leaf. Still without a more thorough history of what the plants have been going thru it's kind of hard to be certain what's going on. It could be that the ph is too high or it could be there is too much phosphorous in the soil and/or not enough nitrogen or it could be a lack of organic material in the soil.

I think I've posted this image before in another thread of yours but in case I haven't I'll post it again here. It's a chart that list the signs of various deficiencies and the most common causes.

As for what's causing the top leaves of the front right plant to be lighter, that could also be a sign of a slight nitrogen deficiency which can also result from a ph that's too low. Whatever is going on it doesn't look like to major a problem at the moment. Maybe do the next watering of two with just plain water and if you can make sure the ph is right around 6.5.