PLANT NUTRITION

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THE UNIVERSITY OF ZAMBIA
SCHOOL OF AGRICULTURAL SCIENCES
SOIL SCIENCE DEPARTMENT
NAME: CHISENGELE LEWIS
COMPUTER NUMBER: 2018254006
COURSE: AGS 6211
TASK: TERM PAPER
DATE DUE: 17TH MAY 2019
QUESTION: How does our knowledge and understanding of Plant Nutrition Principles affect
Crop and land management aspects? In giving the answer to the above question, provide specific
examples.

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Table of Contents
INTRODUCTION..............................................................................................................................3
PLANT NUTRIENTS.........................................................................................................................4
ESSENTIAL ELEMENTS..............................................................................................................4
NUTRIENTS – THEIR FUNCTIONS,MOBILITY IN PLANTS ANDDEFICIENCY/ TOXICITY
SYMPTOMS..............................................................................................................................4
MACRONUTRIENTS........................................................................................................................6
Mineral elements ............................................................................................................................6
MICRONUTRIENTS.........................................................................................................................8
Beneficial nutrients .......................................................................................................................11
NUTRIENT- WATER INTERACTIONS ..........................................................................................12
Soil Moisture Level and Nutrient Absorption..................................................................................13
Mobility in the Soil....................................................................................................................13
NUTRIENT DEMAND AND SUPPLY.............................................................................................14
The Law of the Minimum And Its Implications...............................................................................14
THE SOIL AS PLANT GROWTH MEDIUM....................................................................................16
Soils as a Basis for Crop Production...............................................................................................16
Soil Components ..........................................................................................................................17
Mineral.....................................................................................................................................17
Soil Fertility and Crop Production .....................................................................................................18
Soil Properties and Plant Requirements ..........................................................................................19
Soil Quality Affects Agricultural Productivity.............................................................................19
FERTILIZERS.................................................................................................................................20
Acidity and Basicity of Fertilizers ..............................................................................................21
INTEGRATED NUTRIENT MANAGEMENT..................................................................................24
ADVANCES IN PLANT NUTRITION.............................................................................................25
The Case of Precision Agriculture..................................................................................................25
CONCLUSION................................................................................................................................26
REFERENCES.................................................................................................................................26

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INTRODUCTION
For over 150 years, scientists have studied plant nutrition with goals of understanding the
acquisition, accumulation, transport, and functions of chemical elements in plants (Barker and
Pilbeam, 2007). From these studies, much information has been obtained about the growth and
composition of plants in response to soil-borne elements and to fertilization of crops in the soil or
in soil-less media, as in hydroponic culture of plants (Barker and Pilbeam, 2007). This has come
to be known as plant Nutrition which can be defined as “the supply and absorption of chemical
compounds needed for growth and metabolism” (Mengel and Kirkby, 1987). These chemical
compounds are known as Nutrients and are converted into cellular materials or used for energy
purposes through a process known as Metabolism (Mengel and Kirkby, 1987). A plant nutrient is
a chemical element that is essential for plant growth and reproduction (Chapman, 1966).
Essential element is a term often used to identify a plant nutrient. The term nutrient implies
essentiality, so it is redundant to call these elements essential nutrients. Higher plants require
essential nutrients in inorganic forms exclusively, a feature that distinguishes them from animals
and man and other microorganisms which additionally require organic foods.
However, for an element to be essential, it must follow a three point criteria developed by
ARNON and STOUT (1939);
1. A deficiency of the element makes it impossible for the plant to complete its life cycle.
2. The deficiency is specific for the element in question
3. The element is directly involved in the nutrition of the plant, as for example as a
constituent of an essential metabolite or required for the action of an enzyme system.
This therefore, means that If an element does not meet all of these requirements, for example,
being required by some plants or only enhancing the growth of plants, the element may be a
beneficial element and not an essential element.

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PLANT NUTRIENTS
ESSENTIAL ELEMENTS
As discussed in the introduction, there are three categories of Nutrients which will be discussed
in this paper. It has been mentioned that the term essential element is often used to identify a
plant nutrient and that the term nutrient implies essentiality. Moreover, higher plants require
essential nutrients in inorganic forms exclusively (Mengel and Kirkby, 1987). Below is a brief
discussion of the Macronutrients, Micronutrients and beneficial elements in relation to plant
nutrition, crop and land management. Specifically their roles/functions in plant growth and
development, availability in soil, deficiency symptoms in plants and soil amendments are
discussed.
A total of only 16 elements are essential for the growth and full development of higher green
plants according to the criteria laid down by Arnon and Stout (1939). These criteria are:
1) A deficiency of an essential nutrient makes it impossible for the plant to complete the
vegetative or reproductive stage of its life cycle.
2) Such deficiency is specific to the element in question and can be prevented or corrected
only by supplying this element.
3) The element is involved directly in the nutrition of the plant quite apart from its possible
effects in correcting some unfavorable microbiological or chemical condition of the soil
or other culture medium.
NUTRIENTS – THEIR FUNCTIONS, MOBILITY IN PLANTS AND DEFICIENCY/
TOXICITY SYMPTOMS
Some knowledge of the properties and functions of plant nutrients is helpful for their efficient
and effective management of crops and land, thus, for good plant growth and high yields.
Available nutrients in the soil solution can be taken up by the roots, transported to the leaves and
used according to their functions in plant metabolism. Nutrient ions are of extremely small size,
i.e. like atoms. For example, there are more than 100 000 million K+ cations within a single leaf
cell and more than 1 000 000 molybdate anions, the micronutrient required in the smallest
amount. In general, N and K make up about 80 percent of the total mineral nutrients in plants; P,
S, Ca and Mg together constitute 19 percent, while all the micronutrients together constitute less

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than 1 percent. Most plant nutrients are taken up as positively or negatively charged ions (cations
and anions, respectively) from the soil solution (Havlin et al, 2014). However, some nutrients
may be taken up as entire molecules, e.g. boric acid and amino acids, or organic complexes such
as metal chelates and to a very small extent urea (Marschner, 1995). Whether the original
sources of nutrient ions in the soil solution are from organic substances or inorganic fertilizers,
ultimately, the plants absorb them only in mineral forms. Plants exhibit many shades of
greenness but a medium to dark green colour is usually considered a sign of good health and
active growth. Chlorosis or yellowing of leaf colour can be a sign of a marginal deficiency and is
often associated with retarded growth (Johnston, 2000). Chlorosis is a light green or rather
yellowish discoloration of the whole or parts of the leaf caused by a lower content of
chlorophyll. Because the cells remain largely intact, the chlorotic symptoms are reversible, i.e.
leaves can become green again after the missing nutrient (responsible for chlorophyll formation)
is added. A severe deficiency results in death of the tissue (necrosis). Necrosis is a brownish
discoloration caused by decaying tissue, which is destroyed irreversibly. Necrotic leaves cannot
be recovered by addition of the missing nutrient, but the plant may survive by forming new
leaves. Deficiency symptoms can serve as a guide for diagnosing limiting nutrients and the need
for corrective measures (Brady and Weil, 2002). However, chlorotic and necrotic leaves might
also result from the toxic effects of nutrients, pollution and also from disease and insect attacks.
Therefore, confirmation of the cause is important before corrective measures are taken.
Chemical Nature
The nutrients can be classified into cations and anions and metals and non-metals based on their
chemical nature.
Cations: K, Ca, Mg, Fe, Mn, Zn, Cu,
Anions: NO3, H2, PO4, SO4
Metals: K, Ca, Mg, Fe, Mo, Zn, Cu,
Non-metals: N, P, S, B, Mo, Cl

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MACRONUTRIENTS
The nutrients required in large quantities are known as macronutrients. They are N, P, K, Ca,
Mg, and S. Among these, N, P and K are called primary nutrients and Ca, Mg and S are known"
as secondary nutrients. The later are known as secondary nutrients as they are inadvertently
applied to the soils when N, P and K fertilizers, which contain these nutrients, are used.
Carbon
It is available in abundance from air. Green plants for photosynthetic activities use CO2. It is
also required for cell formation in plants. About 45% or more part, of the plant tissues is made up
of carbon.
Hydrogen
It is essential for cell and tissue formation in plants. This is obtained from water and is required
for energetic reactions. It forms about 6% parts of the plant tissues.
Oxygen
Plants take oxygen from air and water. It forms about 43% parts of the plant structure. It is
required for photosynthetic and respiratory activities. It helps in formation of tissues and cells.
Mineral elements
Nitrogen
It is a major structural part of the cell. Cytoplasm and the particulate fractions of the cell
organelles contain nitrogen in varying amounts, which exist in combination with C, H, O, P and
S. Primary cells are found to have about 5% of nitrogen. It plays a vital role in various metabolic
activities of plants and is a constituent part of amino acids, proteins, nucleic acids, porphyrins,
flavins, purine and pyrimidine nucleotides, enzymes, co-enzymes and alkaloids. It helps in
harvesting solar energy through chlorophyll, in energy transformation through phosphorylated
compounds, in transfer of genetic information through nucleic acids. Besides, it is essential in
cellular and protein metabolism and acts as biological catalyst.

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Phosphorus
It plays a vital role as a structural component of cell constituents and metabolically active
compounds. It is a structural part of the membrane system of the cell, the chloroplasts and
mitochondria. It is a part of sugar phosphates-ADP, ATP, etc. nucleic acids, nucleoproteins,
purine, pyrimidine nucleotides, flavin nucleotides and many co-enzymes viz. NADP, pyridoxyl
phosphate and thiamine phosphate. The most essential constituents of plant cells like esters,
phosphatides and phospholipids are synthesized by phosphorus when it combines with different
organic acids. It also plays an important role in energy transformations and various metabolic
activities of plants. Being a constituent of adenosine phosphate, phosphoglyceraldehyde and
ribulose phosphate, it helps in basic reactions' of photosynthesis and activates several enzymes
participating in dark reactions in photosynthesis.
Potassium
It helps in the maintenance of cellular organization by regulating the permeability of cellular
membranes and keeping the protoplasm in a proper degree of hydration by stabilizing the
emulsions of colloidal particles. Its salts stabilize various enzyme systems. It plays a catalytic
role in activating several enzymes as incorporation of amino-acids in proteins, synthesis of
peptide bonds etc. Presence of potassium is essential for optimal activation of aldehyde
dehydrogenase, phosphate acetyle transferase etc. in vitro. Potassium increases resistance in
plants against drought, heat frost and various diseases caused by fungi nematode and other
micro-organisms. It helps in formation of mechanical tissues in cereals resulting into resistance
to lodging. In fruit crops it improves colour, flavour and increases the size and weight of the
fruits.
Calcium
Calcium regulates the permeability of cellular membrane. It is a structural part of the
chromosomes in which it binds the DNA with protein. It is required by a number of enzymes for
their proper functioning viz. lipase, phosphatase D, £ Amylase and Apyrase. It makes the stems
stiff and thereby reduces lodging in cereals. It also neutralizes the organic acids formed within
the plant body and eliminates their toxic effects. Calcium accelerates nitrogen fixation in
legumes and helps in boosting nitrogen uptake by plants.

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Magnesium
Being constituent part of polyribosomes, it helps in protein synthesis in the plants. Mg is also a
constituent part of chromosomes and chlorophyll. It plays a catalytic role of numerous enzymes
concerning carbohydrate metabolism, phosphate transfer and decarboxilations. It is involved in
photosynthesis and organic acid metabolism. Mg helps in synthesis of fat and increases oil
content in oilseed crops when it combines with Sulphur.
Sulphur
It helps in synthesis of protein and amino acids like cystein, methionine, vitamins (thiamine and
biotine), lipoic acid, acetyl coenzyme A, ferredoxin and glutathione. It forms active sulphate- 3
phosphoadenosine-5 phosphosulphate which synthesizes glucosides in mustard oil, pungency in
onion, radish etc. It is required in conversion of nitrogen into protein in symbiotic nitrogen fixing
legumes. It is involved in activating enzymes participating in the dark reactions of
photosynthesis and carbohydrate metabolism of plants. It increases oil content in soybean,
groundnut and linseed.
MICRONUTRIENTS
The nutrients which are required in small quantities are known as micronutrients or trace
elements. They are Fe, Zn, Cu, B, Mo and Cl. These elements are very efficient and minute
quantities produce optimum effects. On the other hand, even a slight deficiency or excess is
harmful to the plants.
Chlorine
Chlorine (Cl) is absorbed as the chloride anion (Cl-). It is thought to be involved in the
production of oxygen during photosynthesis, in raising cell osmotic pressure and in maintaining
tissue hydration. Deficiency of Cl leads to chlorosis in younger leaves and overall wilting as a
consequence of the possible effect on transpiration. Cl-toxicity symptoms are: burning of the leaf
tips or margins; bronzing; premature yellowing; leaf fall; and poor burning quality of tobacco.

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Copper
Copper (Cu) is taken up as Cu2+. However, Cu uptake is largely independent of competitive
effects and relates primarily to the levels of available Cu in the soil. Cu is involved in
chlorophyll formation and is a part of several enzymes such as cytochrome oxidase. As much as
70 percent of the Cu in plants may be present in the chlorophyll, largely bound to chloroplasts.
Cu is not readily mobile in the plant and its movement is strongly dependent on the Cu status of
the plant. Cu-deficiency symptoms are first visible in the form of narrow, twisted leaves and pale
white shoot tips. At maturity, panicles/ears are poorly filled and even empty where the deficiency
is severe. In maize, yellowing between leaf veins takes place, while in citrus the leaves appear
mottled and there is dieback of new twigs. Excess Cu induces Fe deficiency and, therefore,
chlorosis is a common symptom.
Iron
Fe is absorbed by plant roots as Fe2+, and to a lesser extent as Fe chelates. For efficient
utilization of chelated Fe, separation between Fe and the organic ligand has to take place at the
root surface, after the reduction of Fe3+ to Fe2+. Absorbed Fe is immobile in the phloem. Fe is
generally the most abundant of the micronutrients with a dry-matter concentration of about 100
μg/g (ppm) (Tisdale et al, 1985). It plays a role in the synthesis of chlorophyll, carbohydrate
production, cell respiration, chemical reduction of nitrate and sulphate, and in N assimilation. Fe
deficiency begins to appear on younger leaves first. Yellowing of the interveinal areas of leaves
(iron chlorosis) occurs. In severe deficiency, leaves become almost pale white because of the loss
of chlorophyll. In cereals, alternate yellow and green stripes along the length of the leaf blade
may be observed. Complete leaf fall can occur and shoots can die. Fe toxicity of rice is known as
bronzing. In this disorder, the leaves are first covered by tiny brown spots that develop into a
uniform brown colour. It can be a problem in highly reduced rice soils as flooding may increase
the levels of soluble Fe from 0.1 to 50–100 μg/g Fe within a few weeks. It can also be a problem
in highly weathered, lowland acid soils.
Manganese
Manganese (Mn) is taken up by plants as the divalent ion Mn2+. It is known to activate several
enzymes and functions as an auto-catalyst. It is essential for splitting the water molecule during

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photosynthesis. It is also important in N metabolism and in CO2 assimilation. Like Fe, it is
generally immobile in the phloem. Mn-deficiency symptoms resemble those of Fe and Mg
deficiency where interveinal chlorosis occurs in the leaves. However, Mn-deficiency symptoms
are first visible on the younger leaves whereas in Mg deficiency, the older leaves are affected
first. Mn deficiency in oats is characterized by “grey-speck” where the leaf blade develops grey
lesions but the tip remains green, the base dies and the panicle may be empty. Mn-toxicity
symptoms lead to the development of brown spots, mainly on older leaves and uneven green
colour. Some disorders caused by Mn toxicity are: crinkle leaf spot in cotton; stem streak;
necrosis of potato; and internal bark necrosis of apple trees.
Molybdenum
Mo is absorbed as the molybdate anion MoO4
2- and its uptake is controlled metabolically. Mo is
involved in several enzyme systems. Thus, it is involved directly in protein synthesis and N
fixation by legumes. Mo appears to be moderately mobile in the plant. This is suggested by the
relatively high levels of Mo in seeds, and because deficiency symptoms appear in the middle and
older leaves. Mo deficiency in legumes can resemble N deficiency because of its role in N
fixation. Mo deficiency can cause marginal scorching and rolling or cupping of leaves and
yellowing and stunting in plants. Yellow spot disease in citrus and whip tail in cauliflower are
commonly associated with Mo deficiency.
Zinc
Zn is taken up as the divalent cation Zn2+. Zn is required directly or indirectly by several
enzymes systems, auxins and in protein synthesis, seed production and rate of maturity. Zn is
believed to promote RNA synthesis, which in turn is needed for protein production. The mobility
of Zn is low. The rate of Zn mobility to younger tissue is particularly depressed in Zn-deficient
plants.
Common symptoms of Zn deficiency are: stunted plant growth; poor tillering; development of
light green, yellowish, bleached spots; chlorotic bands on either side of the midrib in monocots
(particularly maize); brown rusty spots on leaves in some crops, which in acute Zn deficiency as
in rice may cover the lower leaves; and in fruit trees the shoots may fail to extend and the small
leaves may bunch together at the tip in a rosette-type cluster. Little-leaf condition is also a

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common symptom. Internodes are short. Flowering, fruiting and maturity can be delayed. Shoots
may die off and leaves can fall prematurely. Deficiency symptoms are not the same in all plants.
Zn toxicity can result in reduction in root growth and leaf expansion followed by chlorosis. It is
generally associated with tissue concentrations greater than 200 μg/g Zn (Marschner, 1995).
Boron
It regulates development and differentiation of vascular tissues formation and lignification of
cell-wall. It is associated with reproductive phase in plants and under imbalanced nutrition it
causes sterility and malformation in reproductive organs. It is involved in carbohydrate
metabolism, particularly in translocation of photosynthates. It boosts nodulation in legumes,
regulates water absorption and is essential for synthesis of ATP, DNA, RNA and pectins
Beneficial nutrients
Several elements other than the essential nutrients have beneficial functions in plants. Although
not essential (as the plant can live without them), beneficial nutrients can improve the growth of
some crops in some respects. Some of these nutrients can be of great practical importance and
may require external addition:
Cobalt
It is required for symbiotic and non-symbiotic nitrogen fixation. It is a part of vitamin B-12.
Sodium
It maintains the osmotic pressure. It also regulates water uptake by plants. Plants take sodium as
a substitute for potash under deficient potash supply.
Nickel (Ni): a part of enzyme urease for breaking urea in the soil, imparts useful role in disease
resistance and seed development.
Silicon (Si): for stalk stability of cereals particularly rice (uptake as silicate anion).
Aluminium (Al): for tea plants (uptake as Al3+ or similar forms).

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NUTRIENT- WATER INTERACTIONS
Even in regions where annual precipitation exceeds growing season evapotranspiration, water
stress frequently limits crop production on the majority of agricultural lands. Stresses caused by
nutrient deficiencies, pests, and other factors reduce the plants' ability to use water efficiently,
which reduces productivity and profit. As pressures grow for increased industrial, recreational,
and urban use of water, agriculture will have less access to water for irrigation. Increasing water
use efficiency is a major challenge to agriculture. It is estimated that overall efficiency of water
in irrigated and dry land farming is 20 to 50%. In general, any growth factor that increases yield
will improve the efficiency of water use. Water Use Efficiency Water use efficiency (WUE) is
the yield of crop per unit of water-from the soil, rainfall, and irrigation. When management
practices increase yields, WUE is increased. Yields of crops have increased greatly in the past 20
years on essentially the same amount of water, which is directly related to improved soil and
crop management practices. For example, tillage systems that leave large amounts of surface
residues conserve water by
1. Increased water infiltration.
2. Decreased evaporation from the surface.
3. Increased snow collection.
4. Reduced runoff. In many parts of the world irrigation has stabilized production, but yields per
unit of land have not increased greatly. After the lack of moisture is eliminated by irrigation,
many factors may limit yields. Because of these other factors, there can be many
disappointments. If yields of 300 bu/a rather than 150 bu/a of corn or 14 tons/a rather than 7
tons/a of alfalfa are to be obtained, the nutrient removal is at least doubled. This means that the
crop must obtain more nutrients from some source, whether from native soil supply, manures, or
fertilizers. How Water Is Lost from the Soil Water in a soil is lost in three ways:
1. From the soil surface by evaporation.
2. Through the plant by transpiration.
3. By percolation beyond the rooting zone.

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The sum of the water used in transpiration and evaporation from soil plus intercepted
precipitation is called evapotranspiration. With more complete cover, less water evaporates from
the soil and more goes through the plant. Adequate fertility and satisfactory stands are among
those factors that help to provide more plant cover rapidly and thus realize more benefit from the
water.
Soil Moisture Level and Nutrient Absorption
Water is a key factor in nutrient uptake by root interception, mass flow and diffusion
(Marschner, 1995). Roots intercept more nutrients, especially Ca2+ and Mg2+, when growing in a
moist soil than in a drier one because growth is more extensive (Havlin et al, 2006). Mass flow
of soil water to supply the transpiration stream transports most of the NO3
-, SO4
- , Ca2+, and
Mg2+ to roots (Mengel and Kirkby, 1987). Nutrients slowly diffuse from areas of higher
concentration to areas of lower concentration but at distances no greater than 1/8 to 1/4 in. The
rate of diffusion depends partly on the soil water content; therefore, with thicker water films or
with a higher nutrient content, nutrients diffuse more readily (Havlin et al, 2006). Nutrient
absorption is affected directly by the level of soil moisture, as well as indirectly by the effect of
water on the metabolic activity of the plant, soil aeration, and the salt concentration of the soil
solution (Havlin et al, 2014). Of course, crop yield potential is always greater with normal or
higher moisture availability. Adequate nutrient availability greatly reduces drought-related yield
losses. Dryland Soils Moisture is the most limiting factor in crop productivity in semiarid and
arid regions (Prasad and Power, 1997). In crop-fallow systems, conserving soil water may not
always increase the grain yield in some crops, but increased soil water conservation will reduce
the dependence on fallowing through more intensive cropping (Prasad and Power, 1997).
Mobility in the Soil
Mobility of nutrients in the soil has considerable influence on availability of nutrients to plants
and method of fertilizer application. For plants to take up these nutrients, two processes are
important (adapted from Brady and Weil, 2002):
(1) Movement of nutrient ions to the absorbing root surface, and
(2) Roots reaching the area where nutrients are available. In the case of immobile nutrients, the
roots have to reach the area of nutrient availability and forage volume is limited to root surface

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area. For highly mobile nutrients, the entire volume of the root zone is forage area. Based on the
mobility in the soil, the nutrient ions can be grouped as mobile, less mobile and immobile. The
mobile nutrients are highly soluble and are not adsorbed on clay complex; e.g.: N03
- , S04
2- , B03
-
, Cl- , Mn2+. Less mobile nutrients are also soluble, but they are adsorbed on clay complex and so
their mobility is reduced; e.g.: NH+, K+, Ca+, Mg++, Cu++. Immobile nutrient ions are highly
reactive and get fixed in the soil; e.g.: HPO4
2-, H2PO4
- , and Zn++. Mobility in Plants Knowledge
of the mobility of nutrients in the plant helps in finding what nutrient is deficient. A mobile
nutrient in the plant moves to the growing points in case of deficiency.
Deficiency symptoms, therefore, appear on the lower leaves.
NUTRIENT DEMAND AND SUPPLY
Plants require nutrients in balanced amounts depending on their stage of development and yield
levels. For optimal nutrition of crops, a sufficient concentration of the individual nutrients should
be present in the plant leaves at any time. An optimal nutrient supply requires:
 Sufficient available nutrients in the root-zone of the soil;
 Rapid transport of nutrients in the soil solution towards the root surface;
 Satisfactory root growth to access available nutrients;
 Unimpeded nutrient uptake, especially with sufficient oxygen present;
 Satisfactory mobility and activity of nutrients within the plant.
The nutrient concentrations required in plants, or rather in the active tissues, are usually
indicated on a dry-matter basis, as this is more reliable than on a fresh-matter basis with its
varying water content. Leaves usually have higher nutrient concentrations than do roots. These
are usually stated as a percentage for macronutrients and in micrograms per gram (parts per
million) for micronutrients.
The Law of the Minimum And Its Implications
In plant nutrition, there is a law known as Liebig’s law of the minimum. It is named after its
author, Justus von Liebig, who said that the growth of a plant is limited by the nutrient that is in
shortest supply (in relation to plant need) (Marschner, 1995). Once its supply is improved, the
next limiting nutrient controls plant growth. This concept has been depicted in many ways. One

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is to imagine a barrel with staves of different heights: Such a barrel can only hold water up to the
height of its shortest stave. The barrel can be full only when all its staves are of the same size. A
plant can also produce to its full potential when all nutrients (production factors in an enlarged
sense) are at an optimal level, i.e. without any deficiencies or excesses. In order to produce high
yields, plant nutrition requires a continuous effort to eliminate minimum factors and provide
balanced nutrition in the optimal range (Marschner, 1995). Even if the law of the minimum is
only a guiding rule, it serves as a useful basis for nutrient management. In a broader sense, the
law of the minimum can be extended to include all production inputs, not only nutrients.
Important aspects of the influence of nutrient supply on plant growth are:
 Plants need certain concentrations of nutrient in their tissue for active growth.
 Nutrient requirement comes somewhat in advance of plant growth.
 Deficiency symptoms indicate a severe shortage of the nutrient in question.
 High yields are only obtained where all nutrients are in the optimal supply range.
 The nutrient with the lowest (minimum) supply determines the yield level.
 Many mistakes in fertilization can be attributed to disregarding the law of the minimum.
 It is easier to correct nutrient deficiencies than to eliminate nutrient toxicities. Nutrient
uptake in time and contents.
During vegetative growth, the daily nutrient uptake increases as growth progresses and
reaches a maximum during the main growing period. N, P and K are mainly taken up during
active vegetative growth for high photosynthetic activity. The rate of N uptake generally
exceeds the rate of dry- matter production in the early stages. Phosphate has an additional
small peak requirement for early root growth. Modern high-yielding grain varieties continue
to absorb P close to maturity and, like N, 70–80 percent of absorbed P ends up in the
panicles or ear heads. For fast-growing crops and high yields, the daily nutrient supply must
be adequate, especially during the period of maximum requirement (Havlin et al, 2014).
Field crops generally absorb K faster then they absorb N and P. In rice, 75 percent of the K
requirement of the plant may be absorbed up to boot leaf stage. Between tillering and
panicle initiation, mean daily absorption rates can approach 2.5 kg (Marschner, 1995).

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THE SOIL AS PLANT GROWTH MEDIUM
Soils as a Basis for Crop Production
Crop production is based largely on soils. Soils are the uppermost part of the earth’s crust,
formed mainly by the weathering of rocks, formation of humus and by material transfer (Tisdale
et al, 1985). Soils vary a greatly in terms of origin, appearance, characteristics and production
capacity (NRC, 1993). Well-developed soils generally show a distinct profile with different
layers. The uppermost layer, called topsoil or A horizon, is richest in organic matter, nutrients
and various soil organisms (Chapman, 1966). Plants mainly use the topsoil as rooting volume to
obtain water and nutrients, but they can also use the subsoil (partly corresponding to B horizon)
or even lower layers up to 1 m or even deeper (Gastal and Lemaire, 2002). Major types of soils
are formed from rocks by weathering processes over long periods extending to more than 1 000
years (Johnstone, 2000). During weathering, physical disintegration of rocks and minerals
occurs, and chemical and/or biochemical soil forming processes lead to their decomposition. The
result is the synthesis of new products, e.g. clay minerals and humic substances (Johnstone,
2000). Mineral or organic substances can be moved downwards or upwards within the profile,
but they may also be lost by transportation to other places by water and wind erosion
(Marschner, 1995). Some of the most productive soils are the result of distant long-term
geological soil erosion (Havlin et al, 2006). Soils vary largely with respect to their natural
fertility and productivity resulting in plant growth ranging from practically zero (no growth at all
on extreme problem soils) to abundant luxuriant growth of natural vegetation (Canadian
Fertilizer Institute, 1990). However, only a small proportion of world’s soils have a very good
level of fertility (Marschner, 1995). Most soils have only good to medium fertility and some
have very low fertility, and are often referred to as marginal soils (Marschner, 1995). Well-
known fertile soils are deep alluvial soils formed from river mud, organic- matter-rich soils on
loess material, nutrient rich Vertisols and volcanic soils.
However, soils with medium fertility can be improved considerably as has been demonstrated in
many countries (Prasad and Power, 1997). Naturally poor or degraded soils can also be restored
to a satisfactory fertility level (Marschner, 1995). Under poor management, soil fertility can be
seriously depleted and soils may become useless for agriculture (Havlin et al, 2006).

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Soil Components
Soil is made up of four main components: mineral, water, air and organic.
Mineral
The mineral component is non-living material. It is divided by the size of the particles, into:
Sand: Rounded particles 1/12 to 1/500 inch (2.0 to 0.06 millimeters) in diameter.
Silt: Rounded particles 1/500 to 1/12,500 inch (0.06 to 0.002 millimeters) in diameter.
Clay: Flattened particles less than 1/12,500 inch (0.002 millimeters) in diameter.
Loam: Mixture of the above in roughly equal proportions. This is the form desirable for plant
growth of most species. Sand has large spaces between the particles, which allow air and water
to move easily, so sand has good aeration and drainage. Clay packs down with only tiny spaces
between particles so there is poor aeration and drainage. However, clay has about 100 times the
surface area as the same volume of sand. More surface area means that clay will hold more water
and more nutrients. Silt has some of the qualities of both sand and clay. Loam combines the best
features of all three: aeration, drainage and storage capacity for water and nutrients. This
understanding is good for effective and efficient crop and land management in that the soil type
desirable is a loam soil, and soil amendments would be targeted at having this scenario.
Water
The need for water in plant growth can never be overemphasized. It suffices to say that the
amount of water in the soil is described in three ways:
1. Saturated: All of the spaces in the soil are filled with water
2. Field capacity: Excess water has drained away leaving a film of water on each particle
and air in the spaces.
3. Wilting Point: The film of water on each particle is so thin that roots can no longer pull
enough water from the soil, so the leaves droop.
Plants grow best when the soil is at field capacity. Frequent watering in controlled amounts on
well-drained soil to maintain field capacity has doubled vegetable yields. However, it takes
careful monitoring and controlled watering to maintain field capacity so usually soil is watered to
near saturation and the excess is allowed to drain away (Brady and Weil, 2002).

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Soil Characteristics
The capacity of soils to be productive depends on more than just plant nutrients. The physical,
biological, and chemical characteristics of a soil—for example its organic matter content, acidity,
texture, depth, and water-retention capacity—all influence fertility (Havlin et al, 2006). Because
these attributes differ among soils, soils differ in their quality. Some soils, because of their
texture or depth, for example, are inherently productive because they can store and make avail-
able large amounts of water and nutrients to plants (Havlin et al, 2006). Conversely, other soils
have such poor nutrient and organic matter content that they are virtually infertile (Marschner,
1995).
Soil Fertility and Crop Production
Soil fertility is a complex quality of soils that is closest to plant nutrient management. It is the
component of overall soil productivity that deals with its available nutrient status, and its ability
to provide nutrients out of its own reserves and through external applications for crop production
(Fageria et al, 1991). It combines several soil properties (biological, chemical and physical), all
of which affect directly or indirectly nutrient dynamics and availability. Soil fertility is a
manageable soil property and its management is of utmost importance for optimizing crop
nutrition on both a short-term and a long-term basis to achieve sustainable crop production. Soil
productivity is the ability of a soil to support crop production determined by the entire spectrum
of its physical, chemical and biological attributes. Soil fertility is only one aspect of soil
productivity but it is a very important one (Chapman, 1966). For example, a soil may be very
fertile, but produce only little vegetation because of a lack of water or unfavourable temperature.
Even under suitable climate conditions, soils vary in their capacity to create a suitable
environment for plant roots. For the farmer, the decisive property of soils is their chemical
fertility and physical condition, which determines their potential to produce crops. Good natural
or improved soil fertility is essential for successful cropping. It is the foundation on which all
input-based high-production systems can be built (Tisdale et al, 1985).

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Soil Properties and Plant Requirements
Plants need anchorage, water and nutrients from the soil but are sensitive to excesses of growth-
impeding substances in the soil. The supply and uptake of nutrients from the soil is not a simple
process but requires a suitable combination of various soil properties:
 Physical properties (depth, texture, structure, pore space with water and air);
 Physico-chemical properties (pH and exchange capacity);
 Chemical and biological properties (nutrient status, their transformation, availability and
mobility).
A major objective of having the most suitable soil physical, chemical and biological
condition is to provide the most favorable environment for the roots to grow, proliferate and
absorb nutrients. Soil physical properties Soil physical properties largely determine the
texture, structure, physical condition and tilth of the soil. These in turn exert an important
influence on potential rooting volume, penetrability of roots, WHC, degree of aeration,
living conditions for soil life, and nutrient mobility and uptake. These are as important as
soil chemical properties.
Soil Quality Affects Agricultural Productivity
A soil’s potential for producing crops is largely determined by the environment that the soil
provides for root growth (Havlin et al, 2014). Roots need air, water, nutrients, and adequate
space in which to develop. Soil attributes, such as the capacity to store water, acidity, depth, and
density determine how well roots develop (Chapman, 1966). Changes in these soil attributes
directly affect the health of the plant. For example, bulk density, a measure of the compactness
of a soil, affects agricultural productivity. When the bulk density of soil increases to a critical
level, it becomes more difficult for roots to penetrate the soil, thereby impeding root growth
(Johnstone, 2000). When bulk density has increased beyond the critical level, the soil becomes
so dense that roots cannot penetrate the soil and root growth is prevented (Johnstone, 2000).
Heavy farm equipment, erosion, and the loss of soil organic matter can lead to increases in bulk
density. These changes in soil quality affect the health and productivity of the plant, and can lead
to lower yields and/or higher costs of production (NRC, 1993).

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FERTILIZERS
Fertilizers are industrially manufactured chemicals containing plant nutrients. Nutrient content is
higher in fertilizers than in organic manures. The nutrients are released almost immediately.
Classification of fertilizers
Fertilizers are classified into straight, complex and mixed fertilizers. Straight fertilizers are those
which supply only one primary plant nutrient, namely nitrogen or phosphorus or potassium (N,
P, and K) (Tisdale et al, 1985). Urea, ammonium sulphate, potassium chloride, potassium
sulphate are some of the straight fertilizers.
Complex fertilizers contain two or three primary plant nutrients of which two primary nutrients
are in chemical combination. These fertilizers are usually produced in granular form. When the
fertilizer contains only two of the primary nutrients, it is designated as incomplete complex
fertilizer, while the one containing all three primary nutrients, (N, P2O5 and K2O) is designated
as complete complex fertilizers.
Mixed fertilizers are physical mixtures of straight fertilizers. They contain two or three primary
plant nutrients. Mixed fertilizers are made by thoroughly mixing the ingredients either
mechanically or manually. Sometimes, complex fertilizers containing two plant nutrients are also
used in formulating fertilizer mixtures. The 'complete fertilizer' is one that contains three major
plant nutrients, namely nitrogen, phosphoric acid and potash. The experimental results obtained
in recent years indicate that for certain soils and crops a complete fertilizer should also carry
other plant nutrients like calcium, magnesium, Sulphur, copper, zinc, etc., while for certain
regions only one or two nutrients would be required. In other words, a complete fertilizer
irrespective of the number of nutrients, should meet the nutritional requirements of the soil and
crops. Every fertilizer mixture is sold with a declared 'fertilizer grade' which refers to the
guaranteed analysis of its plant nutrients. The word analysis, as applied to fertilizers, is used to
designate the percentage composition of the product expressed in terms of N, P2O5 and K2O. A
10-20-10 fertilizer mixture is guaranteed to contain 10 per cent total nitrogen, 20 per cent
available P2O5, 10 per cent water-soluble K2O i.e. Compound D fertilizer.

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Acidity and Basicity of Fertilizers
Application of fertilizers increases acidity or basicity of soils depending on the nature of
fertilizers. Fertilizers which leave an acid residue in the soil are called acid-forming fertilizers.
The amount of calcium carbonate required to neutralize the acid residue is referred to as its
equivalent acidity. For example, 100 kg of ammonium sulphate produces acidity which needs
110 kg of calcium carbonate to neutralize it. Therefore, the acid equivalent of ammonium
sulphate is 110. Fertilizers which leave alkaline residue in the soil are called alkaline forming
fertilizers or basic fertilizers.
Residual Effect of Fertilizers
The extent of residues left over in the soil depends on the type of fertilizer used. Because of their
mobility and solubility, nitrogenous fertilizers leave no residues after the crop is harvested. 15N
studies have shown that only 1 to 2 per cent of nitrogen applied to maize was taken up the
following wheat crop. However, residues of nitrogen occur only when previous crop yields are
poor. Phosphatic fertilizers and farmyard manure leave considerable residue in the soil which is
useful for subsequent crops. Farmyard manure applied to the previous crops: used only 50 per
cent of its nutrients and rest was available for subsequent crops. The residues left by potassium
fertilizers are marginal.
Fertilizer use efficiency
Fertilizers are applied to supplement nutrient requirement of the crop. It should not be looked as
a substitute to organic sources. After determination of nutrient requirement of a crop for a given
yield and contribution of nutrients from different sources, particularly, from the soil source, it is
necessary to supplement the balance from the inorganic sources. These are determined by field
experimentation supplemented by pot-culture, laboratory and green house studies, if necessary.
When a fertilizer is applied all of its nutrient(s) are not absorbed by the crop. The interactions
between soil-crop-season and other factors are quite significant. Only a fraction of the nutrient(s)
is utilized by the crop. Efficiency in any system is an expression of obtainable output with the
addition of unit amount of input. The ratio of energy intake and energy of the produced biomass
i.e. of input and output is called ecological efficiency. Fertilizer use efficiency is the output of
any crop per unit of the nutrient applied under a specified set of soil and climatic conditions
(Tisdale et al, 1975).

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Techniques of increasing fertilizer use efficiency
To increase the fertilizer use efficiency the nutrient must be available at the time of its
requirement by the crop, in right form and quantity (Canadian Fertilizer Institute,1990). On
application there occur certain inevitable/evitable losses of nutrients that reduce the efficiency.
The losses are due to:
 Leaching,
 Volatilization,
 Immobilization,
 Chemical reaction between various components in the mixture,
 Change in capacity to supply nutrients, and
 Unfavourable effects associated with fertilizer application.
Each component of loss can be reduced to a great extent by management of the soil fertilizer-
crop system. This requires knowledge and experience on
 How much of the fertilizer to be applied,
 what/which (type of fertilizer) to be applied,
 When to be applied (time of application),
 How (method of application),
 Where (placement of fertilizer) and
 Other considerations (cost, availability of fertilizer, labour, ease of application,
awareness on benefits of fertilizer use, etc.).
How Much
Inorganic source is a supplement to other sources of nutrients. Among other sources, the most
important one is soil source. Availability of nutrients from soil and fertilizer sources can be
estimated from field experiments involving response to fertilizers and tracer techniques (using
radio-active isotopes). What and Which (Type of fertilizer) Fertilizers vary with respect to their
solubility besides their grade. Choice of fertilizer is location specific and needs to be found out
by field experimentation. The choice is more with respect to nitrogen and phosphatic fertilizers
than for potassic. Nitrogen in form of NO3
- is subject to more leaching. Leaching loss is also

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more in wet than in summer and in sandy soils than in clayey soils. Losses can be minimized by
choosing suitable time and method of application.
When to apply
It necessarily means time of application. The objective of time of application is to get maximum
benefit from the fertilizer nutrient. If the nutrient is applied too earlier than the time of
requirement, it is lost in different ways or is absorbed more than required. If applied late it is
either not absorbed or if absorbed not utilized for the purpose and only gets accumulated in plant
parts. Some amendments need to be applied before commencement of crop season so that it
reacts well with the soil and becomes available to the crop after sowing/planting.
Where to apply (placements)
The objective of placement of fertilizer is to make the nutrient available easily to the crop. It
should be near to the roots. Application may be surface broadcast, at furrow bottom, placed deep
at or slightly below the root zone, top dressed, side dressed or to foliage. This depends on type of
crop, rooting pattern, feeding area and ease of application. The choice of method of application
depends on soil-crop-fertilizer interaction too.
Other considerations
• Proper control of pests and diseases is must for realizing maximum effectiveness from
fertilizers.
• Weeds, if not controlled effectively particularly during early stages (7-21 days) of crop growth
in rainy season, take away about 25 to 30 per cent of the applied plant nutrients. Therefore, the
weed control, particularly during early stages of crop growth is essential.
• When the soils are acidic or saline or alkali, appropriate amendments viz. lime, gypsum etc.
should be applied before using fertilizers. In alkali soils 3 to 5 tonnes of gypsum per acre (8 to 12
t/ha) should be applied broadcast only once and mixed with the top 10 cm of the soil layer
. • Rock phosphates can be profitably used in acid soils and in low land rice and legumes.

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• Deficiency of Zn is becoming increasingly widespread. In such cases 25-50 kg zinc sulphate
should be applied through soil as basal application. If symptoms of zinc deficiency appear in
standing crop, it should be sprayed with 0.3 to 0.5 per cent solution of zinc sulphate mixed with
0.3 percent solution of lime for quick recovery.
• Under adverse soil and climatic conditions e.g. light permeable soils, rainfed conditions or
where the crop is grown under deep standing water, application of fertilizers (particularly N)
through foliage along with insecticides and pesticides (if needed) will lead to higher utilization
efficiency by plants.
INTEGRATED NUTRIENT MANAGEMENT
Soil health degradation with regard to reduced organic carbon (OC) as a result of imbalance use
of fertilizers and multi-nutritional deficiencies (P, K, S, Zn, Fe, Mn, Cu, and B) has emerged as a
major factor responsible for stagnation in agricultural production (Canadian Fertilizer
Institute,1990). Arresting the decline of soil OC by use of organic sources is the most potent
weapon in fighting unabated soil degradation. Organic matter helps in improving soil quality to
sustain biological productivity, maintain environmental quality and promote plant and animal
health. But the organic sources alone are not sufficient to meet the nutritional needs for higher
productivity. As early as 1974 the need for integrated nutrient management (INM) was
elucidated. The INM philosophy combines economic and efficient traditional and improved
technologies from the symbiosis and synergy of crop-soil environment bio-interactions. The
approach is flexible and minimizes use of chemicals but maximizes use efficiency. Therefore,
INM is the most logical way for managing long term soil fertility and productivity. Integrated
nutrient management can bring about equilibrium between degenerative and restorative activities
in the soil environment. In literature three terminologies are used to convey the same meaning –
Integrated Plant Nutrition Systems (IPNS), Integrated Plant Nutrient Supply Systems (IPNS
Systems) and Integrated Nutrient Management (INM). Although these terminologies may look
the same, yet they convey somewhat different connotations.
IPNS Systems means the supply of nutrients to the plants from various sources of nutrients-
 nutrient reserves in the soil

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 organic sources – FYM, compost, green manure, crop residues and other organic
fertilizers and
 fertilizers; IPNS is a concept “which aims at the maintenance or adjustment of soil
fertility and of plant nutrient supply to an optimum level for sustaining the desired crop
productivity through optimization of benefit from all possible sources of plant nutrients in
an integrated manner (Marschner, 1995).
ADVANCES IN PLANT NUTRITION
In the field of Plant Nutrition, there are new and interesting technologies that are being
developed and have greatly improved the efficiency and effectiveness of crop management in
terms of plant nutrition. I have termed this as Advances in Plant Nutrition with Case briefs of
Precision Agriculture. These advances are changing the way Crop and land management are
being done. This will be the future of agriculture.
The Case of Precision Agriculture
Precision agriculture considers spatial variability across a field to optimize application of
fertilizer and other inputs on a site-specific basis (Robert, 1998; Jones, 2000). Precision
agriculture employs technologies of global positioning and geographic information systems and
remote sensing. These technologies permit decisions to be made in the management of crop-
yield-limiting biotic and abiotic factors and their interactions on a site-specific basis rather than
on a whole-field basis (Melakeberhan, 2002). Remote sensing is a term applied to research that
assesses soil fertility and plant responses through means other than on-the-ground sampling and
analysis (Moraghan et al, 2000). Research has applied video image analysis in monitoring plant
growth to assess soil fertility and management (Heiniger, 1999). Spectral reflection and digital
processing of aerial photographs have been researched to assess soil fertility (Heiniger, 1999). In
precision agriculture, it is possible for the fertilizer spreader on the back of a tractor to operate at
different speeds in different parts of a field in response to data obtained on the growth of the crop
underneath and stored in a geographic information system. These data may have been obtained
by remote sensing or even by continuous measurement of yields by the harvesting equipment
operating in the same field at the previous harvest. The precise location of the fertilizer spreader
at any moment of time is monitored by global positioning.

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CONCLUSION
Increasing agricultural production by improving plant nutrition management, together with a
better use of other production factors, is a complex challenge. Agricultural intensification
requires increased flows of plant nutrients to crops, a higher nutrient uptake and higher stocks of
plant nutrients in soils. This also results in a higher production of crop residues, manure and
organic wastes. Excessive use of nutrients, inefficient management of cropping systems, and the
inefficient use of residues and wastes result in losses of plant nutrients, which means an
economic loss for the farmer. On the other hand, an inadequate or insufficient use of plant
nutrients creates an insidious depletion of the stock of plant nutrients on the farm, which will
also mean an economic loss for the farmer. Environmental hazards can be created by applying
too much nutrient compared with the uptake capacity of cropping systems, while the depletion of
nutrient stocks is a major, but often hidden, form of environmental degradation. Plant nutrition
management depends largely on prevailing economic and social conditions. Farmers’ decisions
depend on their economic situation and their socio-economic environment, on their perception of
economic signals and on their acceptance of risks. Plant Nutrition Systems (IPNS) which
enhance soil productivity through a balanced use of local and external sources of plant nutrients
in a way that maintains or improves soil fertility and is environmentally-friendly.
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