Plant analysis using modern techniques reveals that plant body contains about 30 elements and in some cases as many as 60 elements. The presence of several elements in plant does not mean that all these are essential for plants. For an element to be considered an essential plant nutrient, the following three criteria as proposed by Arnon and Stout (1938) and again refined by Arnon (1954) must be satisfied. These are:
1The plant cannot grow or complete its life cycle in absence of the element.
2.The element is very specific and cannot be replaced by another elements.
3. The element plays a direct role in metabolism.