Classification of Plants Mineral Nutrition

Classification of minerals

1. Classification of minerals based on their quantity

Essential elements are classified as Macronutrients, Micronutrients and Unclassified minerals based on their requirements. Essential minerals which are required in higher concentration are called Macronutrients. Essential minerals which are required in less concentration called are as Micronutrients.

Historical events in mineral nutrition

Van Helmont (1648) – made first observation of mineral nutrition, noticed over a period of 5 years soil lost only 56 g in nourishing a seedling into tree. Increase in organic substance comes from water alone.

Wood word (1699) – Soil provides mineral nutrients required for their growth.

De Saussure (1804) – plant growth depends on nitrogen and other elements absorbed by roots from soil.

Liebig     (1840) – gave the “law of minimum” which states that productivity of soil depends on amount of essential elements present in minimum quantity.

Julius Von Sachs (1860) – Demon-strated growing a plant in a defined nutrient solution.

William Frederick Goerick (1940) – Gave the term Hydroponics and com-mercial technique.

Minerals like Sodium, Silicon, Cobalt and Selenium are not included in the list of essential nutrients but are required by some plants, these minerals are placed in the list of unclassified minerals. These minerals play specific roles for example, Silicon is essential for pest resistance, prevent water lodging and aids cell wall formation in Equisetaceae (Equisetum), Cyperaceae and Gramineae (Table 12. 1).

2. Classification of minerals based on mobility

If you observe where the deficiency symptoms appear first, you can notice differences in old and younger leaves. It is mainly due to mobility of minerals. Based on this, they are classified into 1. Actively mobile minerals and 2. Relatively immobile minerals (Figure 12.1).

a.  Actively mobile minerals

Nitrogen, Phosphorus, Potassium, Magnesium, Chlorine, Sodium, Zinc and Molybdenum.

Deficiency symptoms first appear on old and senescent leaves due to active movement of minerals to younger leaves.

b.  Relatively immobile minerals

Calcium, Sulphur, Iron, Boron and Copper shows deficiency symptoms first that appear on young leaves due to the immobile nature of minerals.

3. Classification of minerals based on their functions

a.  Structural component minerals: Minerals like Carbon, Hydrogen, Oxygen and Nitrogen

b.    Enzyme function: Molybdenum (Mo) is essential for nitrogenase enzyme during reduction of atmospheric nitrogen into ammonia. Zinc (Zn) is an important activator for alcohol dehydrogenase and carbonic anhydrase. Magnesium (Mg) is the activator for RUBP carboxylase-oxygenase and PEP carboxylase.

Nickel (Ni) is a constituent of urease and hydrogenase.

c.     Osmotic Potential: Potassium (K) plays a key role in maintaining osmotic potential of the cell. The absorption of water, movement of stomata and turgidity are due to osmotic potential.

d.    Energy components: Magnesium (Mg) in chlorophyll and phosphorous (P) in ATP.