Mineral nutrition refers to how different inorganic substances or minerals are absorbed, distributed, and metabolised by plants for their physiology, structure, and reproductive processes. Van Helmont conducted the initial investigation on inorganic or mineral nutrition in 1648.
Criteria for Essentiality of Elements
The Nutrients or Mineral elements that are necessary for a plant’s proper growth are referred to as Essential Nutrients or Essential Elements. 17 elements are considered vital. The term “essential mineral element” was first proposed by Arnon and Stout in the year 1939. They established that an element must satisfy the following three requirements to be considered essential.
1. Without the mineral element, a plant must be unable to finish its life cycle.
2. No other mineral element may perform the function of the element.
3. The element must be required for a specific metabolic phase, such as an enzymatic reaction, or it must be directly involved in plant metabolism, such as being a part of an enzyme that is an essential plant component.
Beneficial elements are those that promote growth but are not needed for all plant species or may become essential for some species under particular circumstances. Crop plants’ genetic potential cannot be maximised if the agricultural production system does not have advantageous components.
According to the essentiality criterion, mineral elements are required for specific metabolic processes in plants. Therefore, depending on the demand for a nutrient element to generate maximum plant growth, the nutrient is referred to as either Macronutrient or Micronutrient.
The Macronutrients are required in larger quantities and are available in plant tissues in amounts ranging between 0.2 and 4.0 % (on a dry weight basis).
While the amount of micronutrients in plant tissue is less than 0.02% and ranges from 5 to 200 ppm.
According to their needs, the macronutrients are further divided into primary macronutrients, which include nitrogen, phosphorus, and potassium, and secondary macronutrients, which include calcium, sulphur, and magnesium. Another classification of nutrients into metals (K, Ca, Mg, Fe, Mn, Zn, Cu, Mo, Ni) and non-metals is (N, S, P, B, Cl). However, rather than physiochemical characteristics, the most common classification is based on the quantity of mineral element requirements.
Importance of Macro and Microelements
The Macro- and Micronutrient elements can be divided into four groups as shown below (Malik and Srivastava 1982) for ease of understanding.
1. Nitrogen(N) and Sulphur(S) have covalently linked components of biological matter that are present in reduced form
2. Phosphate, borate, and silicate are examples of oxyanions that appear as P, B, and Si.
3: K, Na, Mg, Ca, and Cl play distinct roles in enzyme conformation and catalysis in addition to being engaged in osmoregulation and ionic equilibrium (e.g. metalloprotein complexes)
4: Metalloproteins or structural chelates of Fe, Cu, Mo, and Zn are present and also participate in oxidation-reduction (redox) reactions (first three elements)