Sulphur (S) deficiency
The initial symptoms
are the yellowing of the entire leaf including veins
usually starting with the younger leaves. Leaf tips may
yellow and curl downward. Sulfur deficiencies are light
green fruit or younger leaves with a lack of succulence.
Elongated roots and woody stem. Although it's hard to
see in figure 19, the upper stems of this plant are
purple. Although many varieties of cannabis do get
purplish stems, the trait generally extends the entire
length of the plant's stem, and not just near the top as
in this specimen.