A farmer adds/supplies Na, Ca, Mg and Fe regularly to his field and yet he observes that the plants show deficiency of Ca, Mg and Fe. Give a valid reason and suggest a way to help the farmer improve the growth of plants.

Explanation

Plant can tolerate a specific amount of micronutrients. A slight lesser amount of it can cause deficiency symptoms and a slight higher amount can cause toxicity. The mineral ion concentration which reduces the dry weight of the tissues by 10% is called toxic concentration.
This concentration is different for different micronutrients as well as for different plants, e.g. , `Mn^(2+)` is toxic beyond 600 `mu g g^(-1)` for soyabean and beyond `5300 mu g g^(-1)` for sunflower.
It has also been observed that the toxicity of one micronutrient causes the deficiency of other nutrients. To overcome such problems, farmers should use these nutrients in prescribed concentration so that the excess uptake of one element do not reduce the uptake of other element.