LEARNING OBJECTIVES
By the end of this topic, you should be able to:
Plants must have specific elements or compounds called plant essential nutrients to be able to grow, develop, and produce at their best. Plants that lack an essential nutrient cannot complete their life cycle, for example, they will not be able to develop roots properly, the seed will not germinate, the leaves or the flowers might not be developed as they should be. These elements cannot be substituted. Similarly if there is an excessive amount of these elements, the plant may have development issues or even die.
Essential plant elements are put into two categories, namely:
MACRO-NUTRIENTS
These are nutrients required by plants in large quantities. They include nitrogen, phosphorous, carbon, potassium, oxygen, hydrogen, magnesium, calcium, and sulphur. Macro-nutrients are further put into three categories, namely:
Below, we discuss the main macro-nutrients, their functions and symptoms of their deficiency.
Nitrogen. It plays the following roles in plant growth; synthesis of proteins, essential in vegetative growth, formation of chlorophyll, increases the size of cereal grains and regulates the availability of phosphorous and potassium. Its deficiency symptoms include; premature leaf fall, stunted growth, production of pigments other than chlorophyll and leaf chlorosis or yellowish-green coloration.
Phosphorous. It plays the following roles in plant growth; stimulates nodulation, development of roots, essential in cell division, hastens crop maturation, strengthens plant stem and imparts disease resistance in crops. Its deficiency symptoms in plants include; stunted growth, poor root development, purple color on the leaves, dormancy of lateral buds, premature leaf fall, production of small tubers in tuber crops and lodging.
Potassium. Its roles in plant growth include; protein synthesis, aids in translocation, essential in chlorophyll formation, aids in cell division, imparts disease resistance in crops, neutralizes organic acids in plants and promotes root development. Deficiency symptoms of potassium include; leaf curling, premature leaf fall, chlorosis at margins and tips of leaves, lodging due to weak stems, poorly-developed roots and tubers and leaf mottling (brown spots on leaves).
Magnesium. It plays the following roles in plant growth; promotes nitrogen fixation, component of chlorophyll molecule, activates enzymes and in the synthesis of oil in oil crops. Its deficiency symptoms include; weak and slender stalks, interveinal chlorosis, lack of branching in roots, anthocyanin pigments on leaves and death of plant tissues.
Sulphur. Its roles in plant growth include; protein synthesis, activation of certain enzymes, increases the oil content of oil crops, chlorophyll formation and formation of vitamins. Its deficiency symptoms include; thin stems, leaf chlorosis, reduced nodulation, stunted growth and delayed maturity.
Calcium. It has the following roles in plant growth; protein synthesis, elongation of plant apical meristems and root tips, strengthening of plant cell walls and formation of the middle lamellae. Its deficiency symptoms include; leaf chlorosis, leaves may curl up, poor growth of terminal and root tips, weak stems, blossom end rot in tomatoes and premature shedding of flowers and buds.
Carbon. Its roles in plant growth include; formation of plant biomolecules like cellulose and starch and storage and transport of energy in the plant. Its deficiency symptoms include; stunted growth and leaf chlorosis.
Hydrogen. It plays the following roles in plant growth; building sugars, building the plant and helps to drive the electron transport chain. The deficiency symptoms of hydrogen include; leaf chlorosis, poor growth and weak stalks.
Oxygen. Its main role in plant growth is that it is a component of organic and inorganic components. Its deficiency symptoms include; stunted growth and root injuries.
MICRO-NUTRIENTS
Let's look at plant micronutrients. Plant micronutrients are required in small amounts. They are also called trace elements. They include boron, zinc, iron, manganese, copper, chlorine, and molybdenum. They constitute less than 1% of the total dry weight of most plants.
Boron. Boron has multiple functions in a plant. It affects processes like flowering and fruiting, active salt absorption, pollen germination, and cell division. Boron also affects the metabolism of calcium, water, carbohydrates, amino acids and proteins. Many of these functions are achieved through its function in moving highly polar sugars through membranes- by reducing the energy needed to pass the sugar. The fastest-growing parts of a plant die when sugar doesn't get to them rapidly. Boron deficiency also inhibits the uptake of calcium.
Iron. Iron is important for photosynthesis and it is also an enzyme cofactor in plants. Even though Iron is not a structural part of chlorophyll, it plays an important role in its synthesis. The deficiency of iron can cause interveinal chlorosis and necrosis.
Copper. Copper is very important for photosynthesis. It helps in the transport of plant electrons. It plays a part in multiple enzyme processes, necessary for photosynthesis. For example, it is involved in the manufacture of cell walls (lignin). It is hard to find copper in some soils. One of the major deficiency symptoms of copper in plants is chlorosis. The deficiency of copper can cause iron deficiency.
Molybdenum. Molybdenum acts as a cofactor for enzymes required in building amino acids and is also involved in the metabolism of nitrogen. It helps bacteria and other soil organisms to convert nitrogen in the air into soluble nitrogen in the soil. Molybdenum deficiency can be reduced by adding, sodium molybdate, or molybdenum trioxide.
Manganese. Manganese is important for photosynthesis. It is involved in the building of chloroplasts. The deficiency of manganese may cause coloration abnormalities like discolored spots on the foliage. It is often found in toxic amounts in acidic soils.
Zinc. Zinc is required by many enzymes and is important in DNA transcription. A major symptom of zinc deficiency in plants is stunted leaves, also known as "little leaf". It is caused by oxidative degradation of the growth hormone auxin.
Chlorine. It is used by plants as compounded chloride. It is important for osmosis and ionic balance. Chlorine also plays role in photosynthesis.
These are not all plant nutrients. Other plant nutrients include silicon, selenium, cobalt, nickel, and sodium.
Note that plants may require different amounts of nutrients in different stages of growth. For example, during planting and transplanting, plants require relatively higher amounts of phosphorous. Phosphorous facilitates rooting. During the vegetative stage of most plants, nitrogen is required as it supports vegetative growth. Potassium demand is relatively higher during fruiting. For your plants to grow optimally, ensure they have all the essential plant nutrients at the right time and incorrect amounts. Too little causes deficiency and too high may lead to toxicity. Both macronutrients and micronutrients are important to plants.
SUMMARY
We've learnt that;
