Introduction, Definition and Classification of Nutrients

Publisher Summary This chapter provides a brief overview of the history of plant nutrition, defines the term “essential mineral element,” and groups these elements according to their biochemical behavior and physiological functions. An element is considered as essential when a plant is unable to complete its lifecycle due to the element's absence, when it is not replaceable by another element, and when it is directly involved in plant metabolism. Based on their biochemical behavior and physiological function, elements can be classified into four groups. The first group includes the major constituents of organic plant material such as C, H, O, N, and S. These are constituents of amino acids, proteins, enzymes, and nucleic acids and the assimilation of all these nutrients by plants is closely linked with oxidation–reduction reactions. The second group includes phosphorus, B, and Si that are taken up from the soil solution as inorganic anions or acids and occur in this form in plant cells or are bound by hydroxyl groups of sugars to form phosphate, borate, and silicate esters. The third group of plant nutrients is made up of K, Na, Ca, Mg, Mn, and Cl, all of which are taken up from the soil solution in the form of their ions. They are present in ionic form, where they have nonspecific functions such as establishing electro-potentials. The fourth group includes Fe, Cu, Zn, and Mo that predominantly present in plants in chelated form and facilitate electron transport by valency change.