Question

Why is that in certain plants deficiency symptoms appear first in younger parts of the plants while in others they do so in mature organ ?

Answer 1

The mobility of elements plays an important role to determine that deficiency symptoms appear first in younger or older parts of plants. Some elements like N, and K are highly mobile and moves from older parts to younger parts of plants or where they are most needed, so the symptom deficiencies of these elements first appear in older parts of the plants. And another side some elements like as Ca and S are immobile these elements are not transported from the older parts of plants so the symptoms of deficiencies have first appeared in younger parts of the plant.