Introduction

Plants also utilize gaseous elements (C, H and O) taken directly from the atmosphere.

• Woodward (1699) : Plants obtain minerals from soil through root system.
• Liebig (1840) : Source of carbon in the plant is CO₂ obtained from the atmosphere.
• Arnon and Stout (1939) : Criteria for essentiality of elements
• The plant is unable to grow normally and complete its life cycle, in the absence of the elements.
• The element is specific and cannot be replaced by another element.
• The element plays a direct role in the metabolism of the plant.
• Plant ash (obtained heating the dry plant part at 600°C) contains oxides and carbonates of elements.
• About 92 mineral elements present in different plants; 30 in each and every plant.
• Of these 30 elements, 16 elements are necessary for plant growth and are called essential elements, rest nonessential elements.