Plant can tolerate a specific amount of micronutrients. A lesser amount of micro- nutrient can cause deficiency symptoms and higher amount can cause toxicity. The concentration of mineral ion 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., $\mathrm{Mn}^{2+}$ is toxic beyond $600 \mathrm{mgg}^{-1}$; (for soyabean) and (for sunflower) and beyond $5300 \mu \mathrm{gg}^{-1}$. 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 the element.