Plant Nutrition

Introduction

     The plants upon which we depend for the food we eat, and for the oxygen we breathe, depend in turn upon the soil. A good soil supplies the plants with the mineral elements they use. Vigorous, highly productive plants can be grown in solutions of fertilizer minerals in the absence of soil.

Modes of Nutrition in Plants

     Nutrition can be defined as the process by which an organism obtains food which is used to provide energy and materials for its life sustaining activities.

Mineral Content Of Plants

     Almost all the elements present in the soil can enter the plant. About sixty elements have been so far detected to occur in plants. The mineral content of a plant is determined by the analysis of plant ash.

Functional Elements

     The elements, which take part in the metabolic activities of plants, whether essential or non-essential are named as functional elements.

Deficiency Symptoms Of Elements

     The absence or deficiency (not present in the required amount) of any of the essential elements leads to deficiency symptoms. The symptoms develop as hunger signs in the plants and can be studied by hydroponics or water culture or soil-less culture.

Passive Absorption

     It is the absorption of minerals without direct expenditure of metabolic energy. Passive absorption of ions by root system was demonstrated by Briggs and Robertson (1957).

Active Absorption

     Movement of ions from the outer space of the cell to the inner space is generally against the concentration gradient and hence requires energy. This energy is obtained through metabolism either directly or indirectly. Various evidences indicate the active uptake of ions by carrier mechanism.

Nitrogen Metabolism in Plants

     Nitrogen is one of the important elements found in living organisms. Supply of nitrogen from the atmosphere is maintained. Nitrogen is an essential constituent of amino acids and hence the proteins cannot be absorbed by the plants directly from the atmosphere though it contains 79% of nitrogen. Plants can only absorb nitrogen in the form of salts of nitrogen.

Interesting Activities - 1

     Remove the chlorophyll of a few leaves by keeping them in warm alcohol for some time. Wash in distilled water and cut thin sections.

Interesting Activities - 2

     Take a herbaceous plant and cut it into small pieces. Place them in a porcelain crucible in an oven at 100^oC and dry overnight. The dried plant material is then heated to approximately 600^oC in a muffle furnace or over a burner till it is changed to a greyish white ash. Cool the ash. Dissolve it in 20-50 ml of 2-5% acetic acid or HCl. The solution may be heated if needed. Small quantities of ash solution (a few drops or 1 ml) are taken for testing the elements.

Summary

     All plants whether autotrophic or heterotrophic require mineral nutrition for growth and metabolism.