PLANT TISSUE TESTING
Student Learning Objectives. Instruction in this lesson should result in studentsachieving the following objectives:
1 Name the nutrients needed for plant growth.
2 Explain why nutrients are essential to plants.
3 Explain where and how plants can obtain nutrients.
4 Describe environmental conditions that influence nutrient deficiencies.
5 Explain where plants can obtain nutrients if inadequate amounts are present in thesoil.
6 Discuss the nitrogen cycle and its affect on plant nutrition.
Anticipated Problem: What are the nutrients needed for plant growth?
I. Plants need a variety of nutrients in order to survive and carry on the necessary metabolicprocesses of life. Plants require water, carbon dioxide, oxygen, and a variety of essentialminerals in order to survive.
A. About 80–85% of the weight of a fresh plant is water. The remaining part of the plant
contains elements that are absorbed through the roots and used for plant growth.
B. Plants receive most of the nutrients that they need from the growing media, or in the
case of hydroponics, the nutrient solution that the roots are exposed to. In order to
maintain healthy plants, a grower must provide the right type and amount of nutrients
to the media so that the plants can absorb the nutrients and grow.
C. Plant nutrients can be divided into two groups, macronutrients and micronutrients.
D. Macronutrients are needed in large quantities and include atmospheric, primary, and
secondary elements.
1. Carbon, hydrogen, and oxygen make up about 90–95% of the weight of the dry
matter. These three atmospheric macronutrients are nonminerals. Plants acquire
carbon, hydrogen, and oxygen from carbon dioxide (CO2) and water (H2O)
through the process of photosynthesis. The rest of the dry weight is made up of
minerals.
2. The primary macronutrients are nitrogen (N), phosphorus (P), and potassium (K).
3. The secondary macronutrients include calcium (Ca), magnesium (Mg), and sulfur
(S).
E. Those nutrients that are needed in smaller or trace amounts by the plants, but are still
essential to plant growth are called micronutrients. The micronutrients are boron (B),
copper (Cu), chlorine (Cl), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc
(Zn).
F. A soil test can be performed on the soil or a plant tissue test can be performed using thetissues of a plant to determine which nutrients are present or deficient (absent or lacking).When nutrients are deficient in the soil, the plant growth is adversely affected.
Oftentimes, plants visibly show a nutrient deficiency by turning colors. When nitrogen
is deficient in the soil, a plant’s older leaves will start to turn yellow (chlorosis) and eventuallydie. A plant will show purpling in the stem or leaf when phosphorus is deficient inthe soil. Burning or scorching of the leave’s margins may indicate a potassium deficiency.
G. Because macronutrients are needed in larger quantities they are usually the ones that arethe most limiting to plant production and thus are the ones that producers will add to
their crops.
H. Mnemonics (pronounced ni-mon-iks) is the art of improving the memory using a formula.A mnemonic formula has been developed to aid in recalling all sixteen elements.Carbon (C), Boron (B), Hydrogen (H), Oxygen (O), Phosphorus (P), Potassium (K),Nitrogen (N), Sulfur (S), Calcium (Ca), Iron (Fe), Magnesium (Mg), Chlorine (Cl),
Manganese (Mn), Molybdenum (Mo), Copper (Cu), Zinc (Zn).The following mnemonic can be used to help remember the sixteen elements: C. B.HOPKiNS CaFÈ Mighty good Closed Monday Morning See You Zen.
Anticipated Problem: Why do plants need nutrients?
II. In order to be considered essential, an element must meet the following criteria: (a) absenceof the element results in abnormal growth, injury, or death; (b) the plant is unable to completeits life cycle without the element; (c) the element is required for plants in general; and(d) no other element can serve as a complete substitute.
Nutrient
Nitrogen (N)
Element Forms Absorbed
NO3- or NH4+
Function in Plants
Constituent of amino acids(and thus, proteins andenzymes); constituent ofchlorophyll (four N atoms ineach molecule); stimulatescarbohydrate utilization;stimulates root growth and
development; regulatesuptake and utilization of othernutrients
Deficiency Symptoms
Stunted and slow growth;yellowing of lower leaves ofplant; poor root system
Illinois Biological Science Applications in Agriculture Lesson B3–3 • Page 5
Nutrient
Phosphorus (P)
ElementFormsAbsorbed
H2PO4- or HPO4 2-
Function in Plants
Component of ATP (adenosinetriphosphate), whichimplements energy-using
processes in plants; component of DNA and RNA; used in proteins, metabolic
transfer processes, photosynthesis, and respiration; affects cell division, root development,
maturation, flowering and fruiting, and overall crop quality
Deficiency Symptoms
Purpling of the stem, leaf, orveins on the underside ofleaves; stunted growth and
maturity; reduced yields dueto decreased seed and fruitformation; poor root system
Nutrient
Potassium (K)
Element Forms Absorbed
K+
Function in Plants
Activates enzymes; regulatesopening and closing ofstomata; regulates water
uptake by root cells; essentialfor photosynthesis, starchformulation, and translocation
of sugars; aids in nitrogenmetabolism; promotes growthof meristem tissue
Deficiency Symptoms
Burn or scorch of margins ofleaves, particularly olderleaves; lodging; decreasedyields; lack of diseaseresistance; decreased cropquality
Nutrient
Sulfur (S)
Element Forms Absorbed
SO42-
Function in Plants
Essential component of aminoacids and vitamins
Deficiency Symptoms
Yellowing of leaves, lightgreen leaves, slow growth;looks similar to nitrogendeficiency symptoms
Nutrient
Calcium (Ca)
Element Forms Absorbed
Ca2+
Function in Plants
Component of cell walls,needed for cell growth anddivision
Deficiency Symptoms
Terminal leaves may bedeformed, stunted rootgrowth, dead spots in midribs,black color to plant
Nutrient
Magnesium (Mg)
Element Forms Absorbed
Mg2+
Function in Plants
Needed in chlorophyll, used invitamins and amino acids,used in fat and sugarformation, needed for seedgermination
Deficiency Symptoms
Yellowing between veins andleaves may droop
Nutrient
Boron (B)
Element Forms Absorbed
BO3- or B4O72-
Function in Plants
Affects pollen germination,cell division, metabolism ofnitrogen, fruiting, waterregulation, and hormonemovement
Deficiency Symptoms
Death of terminal buds,thickening of leaves, leavescurl and die, lateral buds growand then die
Nutrient
Copper (Cu)
Element Forms Absorbed
Cu2+
Part of enzymes, used inchlorophyll synthesis, catalystin respiration, protein, andcarbohydrate Function in Plants
metabolism
Deficiency Symptoms
Death of terminal leaf buds,yellowing between veins,slowed growth
Nutrient
Chlorine (Cl)
Element Forms Absorbed
Cl-
Function in Plants
Helps in shoot and rootgrowth
Deficiency Symptoms
Wilting of plants, yellowing,leaves turn bronze
Illinois Biological Science Applications in Agriculture Lesson B3–3 •
Nutrient
Iron (Fe)
Element Forms Absorbed
Fe2+, Fe3+
Function in Plants
Found in enzymes, helps toform a variety of compounds,catalyst in chlorophyllsynthesis
Deficiency Symptoms
Yellowor light green inleaves, yellowing betweenveins
Nutrient
Manganese (Mn)
Element Forms Absorbed
Mn2+
Function in Plants
Helps synthesize chlorophyll,serves as a coenzyme
Deficiency Symptoms
Light green between greenveins, leaves then turn white
Nutrient
Molybdenum (Mo)
Element Forms Absorbed
MoO42-
Function in Plants
Used in protein synthesis,needed for some enzymes
Deficiency Symptoms
Causes nitrogen deficiencyand thus similar signs
Nutrient
Zinc (Zn)
Element Forms Absorbed
Zn2+
Function in Plants
Forms chloroplasts, auxins,and starch, needed bylegumes for seed development
Deficiency Symptoms
Roots are abnormal, yellowingbetween veins, leaves becomebronzed or mottled
Macronutrients
Primary
Nitrogen N
Phosphorus P
Potassium K
Secondary
Calcium Ca
Magnesium Mg
Sulfur S
Micronutrients
Boron - B
Copper - Cu
Chlorine - Cl
Iron - Fe
Manganese - Mn
Molybdenum - Mo
Zinc - Zn
Carbon - C
Hydrogen - H
Oxygen - O
Anticipated Problem: Where do plants obtain nutrients and how do they absorb the nutrients?
III. Nutrients are supplied through the growing medium or nutrient solution. Plant analysiscan provide very valuable information to the grower as they make management decisions.When asked what plants need to grow, most people would respond with water, sunlight,and soil. In all actuality, soil is only one type of media that can be used to grow plants. Thereare a number of substances that allow plants to grow.
A. Soil is the outer portion of the Earth’s crust that supports plant growth. Soil contains air,water, minerals, and organic matter.
B. A Soilless medium (one that contains no topsoil) can be used to grow plants since plantsneed the minerals and water from the medium. Examples include perilite and vermiculite.
C. Hydroponics is a method of growing plants in a nutrient solution. The plants in a hydroponicsunit could be supported in a sand or gravel substrate for support or the roots
could be left bare. With bare roots, the plants’ root system can float in the nutrient rich
solution, or the nutrients could be sprayed directly onto the roots.
D. These essential minerals are dissolved in a water or aqueous solution. This solution
moves from the soil or surrounding environment through the root into the xylem.
Translocation is the movement of organic molecules throughout plant tissues. Most of
the water and nutrients are absorbed through the root hairs. With the help of adhesive
and cohesive properties of water, the solution moves upward against the force of gravity
to the various parts of the plant usually the leaves. Most of the water is lost through transpirationvia the stomata. This also aids in the movement of water from the roots to therest of the plant. Metabolic processes use the nutrients for a variety of purposes.
Anticipated Problem: What environmental conditions influence nutrient deficiencies?
IV. Understanding environmental conditions and their effects on the crop can help pinpoint aproblem that is developing. All factors that influence crop growth, response to fertilization,and yield should be evaluated.
A. The measure of alkalinity or acidity of a substance is known as pH. The pH scale runs
from 0 to 14, with 0 being extremely acidic, 7 as neutral, and 14 as extremely basic.
1. Changes in pH can be made by adding sulfur or gypsum to lower pH (make more
acidic) and by adding limestone to increase pH (make more basic). Generally plants
grow best within the pH range of 5.5 to 8.0.
2. The pH value of soil is important to agriculturists because certain nutrients become
unavailable to plants if the pH value is too high or too low. The amount of nitrogen,
phosphorus, and potassium that are available is dependent upon soil pH.
B. The soil must be of good tilth and permeable enough for roots to expand and feed
extensively. A crop will develop a root system 6 feet or more in depth in some soils to get
water and nutrients. A shallow or compacted soil does not offer this root feeding zone.
Wet or poorly drained soils result in shallow root systems.
C. Cool soil temperature slows organic matter decomposition. This lessens the release of
nitrogen, sulfur, and other nutrients. Nutrients are less soluble in cool soils, and that
increases deficiency potential. Phosphorus and potassium diffuse more slowly in cool
soils. Root activity is decreased.
D. Acid soil conditions reduce the availability of calcium, magnesium, sulfur, potassium,
phosphorus, and molybdenum, and increase the availability of iron, manganese, boron,
copper, and zinc.
E. Insect damage is often mistaken for deficiency symptoms. Examine roots, leaves, and
stems for insect damage that may look like or may induce a nutrient deficiency.
F. Close study will show the difference between plant disease and nutrient deficiency.
G. Dry soil conditions may create deficiencies such as boron, copper and potassium.
Drought slows movement of nutrients to the roots.
H. Soluble salts and alkali are problems in some areas. They may cover only part of the
field. They are usually present where a high water table exists, where salt water contaminationhas occurred, or where poor quality water has been used for irrigation.
I. Herbicides and mechanical controls are more important today than ever before. Weeds
rob crop plants of water, air, light, and nutrients. Some weeds may even release substancesthat inhibit crop growth.
J. Some soils develop hardpans (compaction) and require deep tillage. This requires more
phosphorus and potassium to build up fertility.
K. Row width, spacing of plants in the row, and number of plants per acre have important
effects on yields.
L. Irrigation water can contain nitrate, sulfate, boron, potassium, bicarbonate, chlorine andother salts. A water analysis should be used to modify production practices for utilizationof various water sources.
M. Other pollutants can also cause nutrient deficiencies as well as other problems.
Anticipated Problem: If insufficient levels of nutrients are found in the soil, where do theplants get the nutrients that they need?
V. Plants need nutrients to grow, but sometimes insufficient amounts are present in the soil.Without the presence of nutrients in the growing media, the plant may grow poorly, showingstunted growth, unhealthy coloring of the leaves, and may be more prone to disease andinsect problems.
A. Nutrients may become depleted by growing crops. Since crops are harvested, the
organic matter does not break down and return to the soil to replenish the nutrients.
Additionally, nutrients might leach or run out of the medium via water, causing the
grower to continually add the nutrients. The nutrients can sometimes be present in the
growing medium, but they are not available for the plants to take up into their roots
because the pH level in the soil is not conducive to plant growth. Plants have different
pH requirements.
B. As a result, growers must add artificial fertilizers, manure, or other organic matter to thesoil or nutrient solution for the plants to use. Soil or plant tissue tests should be conductedbefore fertilizers are added.
1. A fertilizer is any material that is provided to plants to supply the nutrients needed
for plant growth. Fertilizers vary in the components they contain, the way they are
applied, and the function they serve.
2. When choosing a fertilizer to use, one should always look for the fertilizer analysis
on the bag or box. The fertilizer analysis states the percentage of primary nutrients
(nitrogen, phosphate, and potash) present in the fertilizer. The analysis is written as
3 numbers, for example, (15-10-26). The numbers, always in this order, represent
the percent of nitrogen, phosphorus, and potash, present in the fertilizer. So the
example above has 15% nitrogen, 10% phosphate, and 6% potash. Fillers are made
up of the remaining essential plant nutrients and are used to ensure a more even
application of the fertilizer. The amount of filler in the above example can be calculated:
100-(15 + 10 + 16) = 59. This means that 59% of the fertilizer is filler.
3. If a fertilizer contains all three primary nutrients, it is called a complete fertilizer. If a
fertilizer is lacking any of the three primary nutrients, it is an incomplete fertilizer.
C. Local fertilizer and horticulture companies employ specialists that can help in determiningan appropriate nutrient program based on your varying conditions.
D. Remember that high yields are not the only goal of a plant nutrition program, but that
overall quality and economics play vital roles as well.
Anticipated Problem: What influence does the nitrogen cycle have on plant nutrition?
VI. Nitrogen is a major requirement for plants to grow rapidly and maintain a healthy greencolor. Although the atmosphere is 78% nitrogen gas, it is the most common nutrient deficiencyseen in plants. N2 gas contains a triple bond which is extremely hard to break; thismakes the molecule almost inert. Nitrogen fertilizer is expensive to produce and is thus anexpensive input for farmers. Leguminous crops are able to use atmospheric nitrogen ratherthan rely on the application of fertilizer; this is an important factor in planning a sustainableagriculture program.
A. The nitrogen cycle is the recycling of nitrogen as it moves between the abiotic (non-living)and biotic (living) parts of the environment. The largest proportion of nitrogen at
any given time is found in the biomass or in dead organisms.
1. Every nutrient that an organism uses is recycled throughout the ecosystem. These
cycles are referred to as biogeochemical cycles. The water cycle is another wellknown
example of this process. The phosphorus and potassium cycles act in a similar
manner.
2. The key concept is that no element is lost or consumed in the environment, but
rather it changes form and moves between the abiotic and biotic components of the
environment and is recycled.
B. Nitrogen is essential to all living organisms because of its use in the synthesis of
enzymes, proteins, and chromosomes. In plants, nitrogen is an important component of
chlorophyll.
C. Plants absorb nitrogen as inorganic nitrate ions (NO3-) and in a few cases as ammonium(NH4+) or amino (NH2+) ions.
1. The positive charge of ammonium causes it to easily bond to clay soils making it
unavailable.
2. The negative charge of nitrate causes it to easily leached away; this can become a
cause for water contamination. High nitrite levels in water can cause illness especially
in children.
3. Nitrogen that is absorbed by the plant is reduced toN2-, NH-orNH2 which then is
synthesized into more complex compounds and amino acids and proteins.
4. Nitrogen assimilation is the incorporation of nitrogen into organic cell substances
by living organisms.
D. Most natural soil nitrogen is in the organic form meaning that it is combined in some
manner with carbon. Manures, decomposing organic matter, and urea are all forms of
organic nitrogen. These must be oxidized before plants can use them.
1. The transformation of organic matter to the inorganic or mineral form (NH4+,NO2-, or NO3-) is called mineralization.
2. Immobilization is the conversion of nitrogen from an inorganic or mineral form to
an organic form. This process occurs naturally during initial decomposition or
nitrogen can be immobilized during chemical fertilizer composition to make it
available to the plant at a later time.
E. Nitrogen fixation is the conversion of atmospheric nitrogen into oxidized forms that canbe assimilated by plants.
1. A symbiotic relationship that exists between bacteria and legume plants is utilized to
convert nitrogen gas (N2) to ammonium ions (NH4+) that are usable to plants.
2. Certain blue-green algae and bacteria are capable of biochemically fixing nitrogen.