Premature leaf fall is caused due to the deficiency of

The concentration of an essential element below which plant growth is retarded is termed as .......

Absence of $Mg^{++}$ ions from plant tissue results in

What is the effect of manganese toxicity on other elements in plants?

It is observed that the deficiency of a particular element shows its symptoms initially in older leaves and then in younger leaves. Does it indicate that the element is actively mobilized or relatively immobile?

Which of the following is $NOT$ a deficiency symptom of mineral nutrition?