Fertilizers - Types and their applications

-Huma Naz
humanaz83@gmail.com

Plants, like all other living things need food for their development and growth, and they require 16 essential elements. Hydrogen, carbon and oxygen are derived from the atmosphere and water soil. The remaining 13 essential elements (manganese, nitrogen, calcium, phosphorus, potassium, zinc, magnesium, sulfur, iron, copper, boron, molybdenum, and chlorine) are supplied either from soil minerals and soil organic matter or by inorganic or organic fertilizers. Bio-fertilizers add nutrients through the natural processes of nitrogen fixation, solubilizing phosphorus, and stimulating plant growth through the synthesis of growth-promoting substances. Plants, like all other living things need food for their development and growth, and they require 16 essential elements. Hydrogen, carbon and oxygen are derived from the atmosphere and water soil. Therefore, they are extremely advantageous in enriching soil fertility and fulfilling plant nutrient requirements by supplying the organic nutrients through microorganism and their byproducts. Hence, bio-fertilizers do not contain any chemicals which are harmful to the living soil.

INTRODUCTION 

Plants, like all other living things need food for their development and growth, and they require 16 essential elements. Hydrogen, carbon and oxygen are derived from the atmosphere and water soil. The remaining 13 essential elements (manganese, nitrogen, calcium, phosphorus, potassium, zinc, magnesium, sulfur, iron, copper, boron, molybdenum, and chlorine) are supplied either from soil minerals and soil organic matter or by inorganic or organic fertilizers. The microorganisms in bio-fertilizers restore the soil's natural nutrient cycle and build soil organic matter. Through the use of bio-fertilizers, healthy plants can be grown, while enhancing the sustainability and the health of the soil. Since they play several roles, a preferred scientific term for such beneficial bacteria is "plant-growth promoting rhizobacteria" (PGPR). Therefore, they are extremely advantageous in enriching soil fertility and fulfilling plant nutrient requirements by supplying the organic nutrients through microorganism and their byproducts. Hence, bio-fertilizers do not contain any chemicals which are harmful to the living soil.

1) PLANT NUTRIENTS

1.1 Primary Macronutrients required for Plants

This is in accordance with Justus von Liebig's law of the minimum.^[1] The essential plant nutrients include carbon, oxygen and hydrogen which are absorbed from the air, whereas other nutrients including nitrogen are typically obtained from the soil (exceptions include some parasitic or carnivorous plants).

There are 17 most important nutrients for plants. Plants must obtain the following mineral nutrients from their growing medium:-^[2]

• The macronutrients: 
• nitrogen(N), phosphorus (P), potassium (K), calcium (Ca), sulfur (S), magnesium (Mg), carbon (C), oxygen(O), hydrogen (H)
• the micronutrients (or trace minerals): 
• iron(Fe), boron (B), chlorine (Cl), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), nickel (Ni)

These elements stay beneath soil as salt. So plants consume these elements as ion. The macronutrients are consumed in larger quantities; hydrogen, oxygen, nitrogen and carbon contribute to over 95% of a plants' entire biomass on a dry matter weight basis. Micronutrients are present in plant tissue in quantities measured in parts per million, ranging from 0.1^[3] to 200 ppm, or less than 0.02% dry weight.^[4]

1.1.1 Nitrogen

Although Earth’s atmosphere contains 78% nitrogen gas (N₂), most organism cannot directly use this resource due to the stability of the compound.

Nitrogen is a major constituent of several of the most important plant substances. For example, nitrogen compounds comprise 40% to 50% of the dry matter of protoplasm, and it is a constituent of amino acids, the building blocks of proteins.^[5] All organisms use the ammonia (NH₃) form of nitrogen to manufacture amino acids, proteins, nucleic acids and other nitrogen-containing components necessary for life.

Nitrogen is required for cellular synthesis of enzymes, proteins, chlorophyll, DNA and RNA, and is therefore important in plant growth and production of food and feed. It typically makes up around 4% of the dry weight of plant matter. Inadequate supply of available N frequently results in plants that have slow growth, depressed protein levels, poor yield of low quality produce, and inefficient water use. The sources of nitrogen used in fertilizers are many, including ammonia (NH₃), diammonium phosphate ((NH₄)₂HPO₄), ammonium nitrate (NH₄NO₃), ammonium sulfate (NH₄)₂SO₄), calcium cyanamide (CaCN₂), calcium nitrate (Ca(NO₃)₂), sodium nitrate (NaNO₃), and urea (N₂H₄CO).

1.1.2 Phosphorus

Phosphorus (P) is a major growth-limiting nutrient, and unlike the case for nitrogen, there is no large atmospheric source that can be made biologically available. Root development, stalk and stem strength, flower and seed formation, crop maturity and production, N-fixation in legumes, crop quality, and resistance to plant diseases are the attributes associated with phosphorus nutrition.

Although phosphorus uptake by plants is less compared to nitrogen and potassium, normal plant growth cannot be achieved without it. The concentration of soluble phosphorus (P) in tropical soil is usually very low, phosphorus is only available in micro molar quantities or less.

Phosphorus is concentrated at the most actively growing points of a plant and stored within seeds in anticipation of their germination. Phosphorus is most commonly found in the soil in the form of polyprotic phosphoric acid (H₃PO₄), but is taken up most readily in the form of H₂PO₄. Phosphorus is available to plants in limited quantities in most soils because it is released very slowly from insoluble phosphates and is rapidly fixed once again. Under most environmental conditions it is the element that limits growth because of this constriction and due to its high demand by plants and microorganisms. Plants can increase phosphorus uptake by a mutualism with mycorrhiza.^[6] The P-content in average soils is about 0.05% (w/w) but only 0.1% of the total P is available to plants. Some microorganisms are known to be involved in the solubilization of insoluble phosphate.

1.1.3 Potassium

Potassium (K) concentrations in most plants range from 1 to 4% by weight. Unlike the other primary nutrients, K forms no other compounds in the plant, but remains a lone ion. Potassium is also vital for animal and human nutrition, and thus healthy fruits, vegetables and grains must have adequate levels of K

Potassium regulates the opening and closing of the stomata by a potassium ion pump. Since stomata are important in water regulation, potassium regulates water loss from the leaves and increases drought tolerance. Potassium deficiency may cause necrosis or inter veinal chlorosis. The potassium ion (K⁺) is highly mobile and can aid in balancing the anion (negative) charges within the plant. Potassium helps in fruit coloration, shape and also increases its brix. Hence, quality fruits are produced in potassium-rich soils. Potassium serves as an activator of enzymes used in photosynthesis and respiration.^[6] 

Potassium deficiency may cause necrosis or inter veinal chlorosis, wilting, brown spotting, and higher risk of pathogens. K+ is highly mobile and can aid in balancing the anion charges within the plant. It serves as an activator of enzymes used in photosynthesis and respiration.

Potassium is used to build cellulose and aids in photosynthesis by the formation of a chlorophyll precursor.

Potassium fertilizers: Potassium chloride [KCl], Potassium sulfate [K₂SO₄], Potassium nitrate [KNO₃], Potassium-magnesium sulfate [K₂SO₄. 2MgSO₄].

Sulfur (S), calcium (Ca), and magnesium (Mg) are considered secondary macronutrients because they are less commonly yield-limiting than the primary macronutrients (N, P, and K), yet are required by crops in relatively large amounts.

1.2.1 Calcium

Calcium is one of the main secondary nutrients necessary for healthy plant growth. Important sources of calcium are various fertilizers such as a single and a triple superphosphate, a precipitate, a calcium nitrate, etc. The other way forenriching soils by calcium is liming. For this purpose, a dolomite, a magnesite andvarious calcium carbonate minerals are used.

1.2.2 Magnesium (Mg)

Magnesium is an essential component of chlorophyll, so it is essential for photosynthesis. It also regulates the uptake of other essential elements; serves as a carrier of phosphorus compounds, facilitates translocation and metabolism of carbohydrates. It considered as highly mobile nutrient in plants; relatively immobile insoils. Magnesium is an activator and component of many plant enzymes required in growth process, and enhances production of oils and fats. Magnesium fertilizers include: Dolomite [CaMg(CO₃)₂], Magnesium sulfate, Epsom salts[MgSO₄.7H₂O], Magnesium oxide [MgO] contains 55% Mg .

1.2.3 Sulfur (S)

Integral component of amino acids, therefore essential to protein synthesis. It considered as essential component of oils in aromatic compounds (e.g., garlic and onion), production of chlorophyll, essential for nodule formation on legume roots, increases size and weight of grain crops, aids in seed production. Highly mobile nutrient in plants; mobile in soils.

Sulfur is a structural component of some amino acids (including cystein and methionine) and vitamins, and is essential for chloroplast growth and function; it is found in the iron-sulphur complexes of the electron transport chains in photosynthesis. It is needed for N₂ fixation by legumes, and the conversion of nitrate into amino acids and then into protein.^[7]

1.3 The Micronutrients or Trace Minerals

Boron (Bo): affects water absorption by roots Translocation of sugars;

Chlorine (Cl): isan essential to some plant processes, acts in the enzyme systems;

Manganese (Mn): is essential in plant metabolism, nitrogen transformation;

Iron (Fe): helps in carrying electrons to mix oxygen with other elements;

Zinc (Zn):is important in plants metabolism, helps form growth hormones, and reproduction;

Copper (Cu): helps in the use of iron, and helps respiration;

Molybdenum (Mo): improve plant development, reproduction,

2.TYPES OF FERTILIZERS

There are two types of supplies for agriculture, specifically fertilizer and pesticide. It can be said that fertilizer is food, and pesticide is medicine for plants in conventional agriculture. Among the materials used in agriculture, fertilizer is the most widely used. Based onthe production process, it can be roughly categorized into three types: chemical, organic and biofertilizer.

2.1 CHEMICAL FERTILIZERS (Synthetic Fertilizer)

Fertilizers play an important role in increasing crop production. The main macronutrients present in inorganic fertilizers are nitrogen, phosphorus, and potassium which influence vegetative and reproductive phase of plant growth.

2.1.1 The Advantages of Using Chemical Fertilizers

Nutrients are soluble and available to the plants, therefore the effect is direct and fast, the price is lower and more competitive than organic fertilizer, which makes it more acceptable and often applied by users. They are quite high in nutrient content; only relatively small amounts are required for crop growth.

2.1.2 Disadvantages of Chemical Fertilizers

The use of chemical fertilizers alone has not been helpful under intensive agriculture because it aggravates soil degradation. The degradation is brought about by loss of organic matter which consequently results in soil acidity, nutrient imbalance and low crop yields.

Due to its high solubility, up to 70% of inorganic fertilizer can be lost through leaching, denitrification and erosion and reducing their effectiveness.

Over application can result in negative effects such as leaching, pollution of water resources, destruction of microorganisms and friendly insects, crop susceptibility to disease attack, acidification or alkalization of the soil or reduction in soil fertility.

2.2 ORGANIC FERTILIZERS

Organic fertilizer refers to materials used as fertilizer that occur regularly in nature, usually as a byproduct or end product of a naturally occurring process.

Like any fertilizer, organic fertilizers typically provide the three major macronutrients required by plants: nitrogen, phosphorus, and potassium. Organic fertilizers include naturally occurring organic materials, (e.g. manure, worm castings, compost, seaweed), or naturally occurring mineral deposits.

2.2.1 Types of Organic Fertilizers

1- Animal manures:

Animal manures are probably the most commonly available organic material used for their fertilizer value. Animal manure is essentially a complete fertilizer

2- Sewage sludge:

It is a recycled product of municipal sewage treatment plants. Forms commonly available are activated, composted and lime-stabilized

3- Plant substances

They are often rich in specific nutrients, such as nitrogen.

4- Composts

Although making compost from a variety of raw materials is possible, the finished products are remarkably similar in their final concentrations of nitrogen, phosphorus, and potassium.

 2.2.2 Advantages of Organic Fertilizers

Organic fertilizers are better sources of nutrient in balanced amounts than inorganic fertilizers where soil is deficient in both macro and micronutrients.

Organic based fertilizer use is beneficial because it supplies micronutrients, and organic components that increase soil moisture retention and reduce leaching of nutrients.

Organic fertilizers can be used on acid tolerant and those better suited to neutral or alkaline conditions.

In addition to increasing yield and fertilizing plants directly, organic fertilizers can improve the biodiversity (soil life) and long-term productivity of soil, and may prove a large depository for excess carbon dioxide.

Organic nutrients increase the abundance of soil organisms by providing organic matter and micronutrients for organisms such as fungal mycorrhiza.

2.2.3 Disadvantages of Organic Fertilizers

Hard to get, Not sterile, Low nutrient content, Generally costs significantly more than synthetic fertilizer, Organic certification requires documentation and regular inspections, Organic fertilizers still release nutrients into their surroundings; these nutrients can find their way into local streams, rivers, and estuaries just as nutrients from synthetic sources do.

2.3 BIOFERTILIZERS

Biofertilizers are commonly called microbial inoculants which are capable of mobilizing important nutritional elements in the soil from non-usable to usable form through biological processes.

The term ‘biofertilizer’ include selective micro-organism like bacteria, fungi and algae which are capable of fixing atmospheric nitrogen or convert soluble phosphate and potash in the soil into forms available to the plants. Soil microorganisms play an important role in soil processes that determine plant productivity. Bacteria living in the soil are called free living and some bacteria support plant growth indirectly, by improving growth restricting conditions either via production of antagonistic substances or by inducing resistance against plant pathogens.

The interactions among the rhizosphere, the roots of higher plants and the soil borne microorganisms have a significant role in plant growth and development. The organic compounds, released by roots and bacteria, play an important role in the uptake of mineral nutrient. The hormones produced by the rhizosphere bacteria have direct effects on higher plants. Biofertilizer is most commonly referred to the use of soil microorganisms to increase the availability and uptake of mineral nutrients for plants

2.3.1 Advantages of Biofertilizers

Biofertilizers have definite advantage over chemical fertilizers.

• The use of biofertilizers effectively enrich the soil and cost less than chemical fertilizers, which harm the environment and deplete non-renewable energy sources..
• Chemical fertilizers supply over nitrogen whereas biofertilizers provide in addition to nitrogen certain growth promoting substances like hormones, vitamins , amino acids, etc.,.
• On the other hand biofertilizers supply the nitrogen continuously throughout the entire period of crop growth in the field under favorable conditions.
• Continuous use of chemical fertilizers adversely affect the soil structure whereas biofertilizers when applied to soil improve the soil structure.
• The effects of chemical fertilizers are that they are toxic at higher doses. Biofertilizers, however, have no toxic effects.

The utilization of microbial products has several advantages over conventional chemicals for agricultural purposes: (1) microbial products are considered safer than many of the chemicals now in use; (2) neither toxic substances nor microbes themselves will be accumulated in the food chain; (3) self-replication of microbes circumvents the need for repeated application; (4) target organisms seldom develop resistance as is the case when chemical agents are used to eliminate the pests harmful to plant growth; and (5) properly developed biocontrol agents are not considered harmful to ecological processes or the environment.

2.3.2 Types of Biofertilizers

The following common types of biofertilizers are available to the farmers in various countries

Nitrogen fixing biofertilizers eg. Rhizobium, Bradyrhizobium, Azospirillum and Azotobacter.

Phosphorous solubilising biofertilizers (PSB) eg. Bacillus, Pseudomonas and Aspergillus

Potassium mobilizing biofertilizer Frateuria aurentia

Plant growth promoting biofertilizers eg. Pseudomonas

The products in above table are some examples of biofertilizers which provides N, P, K to the plant.

2.3.3 How biofertilizers work?

Biofertilizers fix atmospheric nitrogen in the soil and root nodules of legume crops and make it available to the plant.

They solubilize the insoluble forms of phosphates like tricalcium, iron and aluminium phosphates into available forms.

They scavenge phosphate from soil layers.

They produce hormones and antimetabolites which promote root growth.

They decompose organic matter and help in mineralization in soil.

When applied to seed or soil, biofertilizers increase the availability of nutrients and improve the yield by 10 to 25% without adversely affecting the soil and environment.

contributed by :
Dr. Huma Naz
humanaz83@gmail.com
Department of Agriculture Coopretion and farmer welfare GOI
Krishi Bhawan Delhi.

REFERENCES:

1. Emanuel Epstein. Mineral Nutrition of Plants: Principles and Perspectives.

2. Allen V. Barker; D. J. Pilbeam (2007). Handbook of plant nutrition. CRC Press. ISBN978-0-8247-5904-9. Retrieved 17 August 2010.

3. Marschner, Petra, ed. (2012). Marschner's mineral nutrition of higher plants (3rd ed.). Amsterdam: Elsevier/Academic Press. ISBN9780123849052.

4. "Archived copy". Archived from the originalon 2010-02-19. Retrieved 2010-02-10.Retrieved Jan. 2010.

5. Swan, H.S.D. 1971a. Relationships between nutrient supply, growth and nutrient concentrations in the foliage of white and red spruce. Pulp Pap. Res. Inst. Can., Woodlands Pap. WR/34. 27 p.

6. Norman P. A. Huner; William Hopkins. "3 & 4". Introduction to Plant Physiology 4th Edition. John Wiley & Sons, Inc. ISBN978-0-470-24766-2.

7. Haneklaus, Silvia; Bloem, Elke; Schnug, Ewald; de Kok, Luit J.; Stulen, Ineke (2007). "Sulfur". In Barker, Allen V.; Pilbeam, David J. Handbook of plant nutrition. CRC Press. pp. 183–238. ISBN978-0-8247-5904-9. Retrieved 12 June 2017.