New leaf is yellow!

Hi everyone,

I'm growing my plant in the backyard and lately the new leaf turns yellow.. pale as you can see in the picture.

I've read and found this

"Sulfur: Young leaves turn pale green, while the older leaves remain green; plant is stunted and spindly..."

Is it the same problem that I'have or could it be some other problem? please advice.

Thanks a lot!

magneseum def i think