PLANT TISSUE TESTINGStudent Learning Objectives. Instruction in this lesson should result in students achieving 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 the soil.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 metabolic processes of life. Plants require water, carbon dioxide, oxygen, and a variety of essential minerals in order to survive.

A. About 80–85% of the weight of a fresh plant is water. The remaining part of the plantcontains 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 thecase of hydroponics, the nutrient solution that the roots are exposed to. In order tomaintain healthy plants, a grower must provide the right type and amount of nutrientsto 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, andsecondary elements.1. Carbon, hydrogen, and oxygen make up about 90–95% of the weight of the drymatter. 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 ofminerals.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 stillessential 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 the tissues 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 nitrogenis deficient in the soil, a plant’s older leaves will start to turn yellow (chlorosis) and eventually die. A plant will show purpling in the stem or leaf when phosphorus is deficient in the 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 are the most limiting to plant production and thus are the ones that producers will add totheir 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) absence of the element results in abnormal growth, injury, or death; (b) the plant is unable to complete its 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.NutrientNitrogen (N) Element Forms Absorbed NO3 - or NH4+ Function in Plants Constituent of amino acids (and thus, proteins and enzymes); constituent of chlorophyll (four N atoms in each molecule); stimulates carbohydrate utilization; stimulates root growth anddevelopment; regulates uptake and utilization of other nutrientsDeficiency SymptomsStunted and slow growth; yellowing of lower leaves of plant; poor root systemIllinois Biological Science Applications in Agriculture Lesson B3–3 • Page 5

NutrientPhosphorus (P) Element Forms Absorbed H2PO4- or HPO4 2- Function in Plants Component of ATP (adenosine triphosphate), which implements energy-usingprocesses in plants; component of DNA and RNA; used in proteins, metabolictransfer processes, photosynthesis, and respiration; affects cell division, root development,maturation, flowering and fruiting, and overall crop qualityDeficiency SymptomsPurpling of the stem, leaf, or veins on the underside of leaves; stunted growth andmaturity; reduced yields due to decreased seed and fruit formation; poor root system

NutrientPotassium (K) Element Forms Absorbed K+ Function in Plants Activates enzymes; regulates opening and closing of stomata; regulates wateruptake by root cells; essential for photosynthesis, starch formulation, and translocationof sugars; aids in nitrogen metabolism; promotes growth of meristem tissueDeficiency Symptoms

Burn or scorch of margins of leaves, particularly older leaves; lodging; decreased yields; lack of disease resistance; decreased crop quality

NutrientSulfur (S)Element Forms Absorbed SO4 2- Function in Plants Essential component of amino acids and vitaminsDeficiency SymptomsYellowing of leaves, light green leaves, slow growth; looks similar to nitrogen deficiency symptoms

NutrientCalcium (Ca) Element Forms Absorbed Ca2+ Function in Plants Component of cell walls, needed for cell growth and divisionDeficiency SymptomsTerminal leaves may be deformed, stunted root growth, dead spots in midribs, black color to plant

NutrientMagnesium (Mg) Element Forms Absorbed Mg2+ Function in Plants Needed in chlorophyll, used in vitamins and amino acids, used in fat and sugar formation, needed for seed germinationDeficiency SymptomsYellowing between veins and leaves may droop

NutrientBoron (B) Element Forms Absorbed BO3- or B4O7 2-Function in Plants Affects pollen germination, cell division, metabolism of nitrogen, fruiting, water regulation, and hormone movementDeficiency SymptomsDeath of terminal buds, thickening of leaves, leaves curl and die, lateral buds grow and then die

NutrientCopper (Cu) Element Forms Absorbed Cu2+ Part of enzymes, used in chlorophyll synthesis, catalyst in respiration, protein, and carbohydrate Function in Plants metabolismDeficiency SymptomsDeath of terminal leaf buds, yellowing between veins, slowed growth

NutrientChlorine (Cl) Element Forms Absorbed Cl- Function in Plants Helps in shoot and root growthDeficiency SymptomsWilting of plants, yellowing, leaves turn bronzeIllinois Biological Science Applications in Agriculture Lesson B3–3 • NutrientIron (Fe) Element Forms Absorbed Fe2+, Fe3+ Function in Plants Found in enzymes, helps to form a variety of compounds, catalyst in chlorophyll synthesisDeficiency SymptomsYellowor light green in leaves, yellowing between veins

NutrientManganese (Mn) Element Forms Absorbed Mn2+ Function in Plants Helps synthesize chlorophyll, serves as a coenzymeDeficiency SymptomsLight green between green veins, leaves then turn white

NutrientMolybdenum (Mo) Element Forms Absorbed MoO4 2- Function in Plants Used in protein synthesis, needed for some enzymesDeficiency SymptomsCauses nitrogen deficiency and thus similar signs

NutrientZinc (Zn) Element Forms Absorbed Zn2+ Function in Plants Forms chloroplasts, auxins, and starch, needed by legumes for seed developmentDeficiency SymptomsRoots are abnormal, yellowing between veins, leaves become bronzed or mottled

MacronutrientsPrimaryNitrogen N Phosphorus P Potassium K SecondaryCalcium Ca Magnesium Mg Sulfur S

MicronutrientsBoron - B Copper - Cu Chlorine - Cl Iron - Fe Manganese - Mn Molybdenum - MoZinc - Zn Carbon - CHydrogen - HOxygen - 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 analysis can 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. There are 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 plants need 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 hydroponics unit could be supported in a sand or gravel substrate for support or the rootscould be left bare. With bare roots, the plants’ root system can float in the nutrient richsolution, 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 ofthe water and nutrients are absorbed through the root hairs. With the help of adhesiveand cohesive properties of water, the solution moves upward against the force of gravityto the various parts of the plant usually the leaves. Most of the water is lost through transpiration via the stomata. This also aids in the movement of water from the roots to the rest 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 a problem 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 runsfrom 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 moreacidic) and by adding limestone to increase pH (make more basic). Generally plantsgrow best within the pH range of 5.5 to 8.0.2. The pH value of soil is important to agriculturists because certain nutrients becomeunavailable 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 feedextensively. A crop will develop a root system 6 feet or more in depth in some soils to getwater 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 ofnitrogen, sulfur, and other nutrients. Nutrients are less soluble in cool soils, and thatincreases deficiency potential. Phosphorus and potassium diffuse more slowly in coolsoils. 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, andstems 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 thefield. They are usually present where a high water table exists, where salt water contamination has occurred, or where poor quality water has been used for irrigation.

I. Herbicides and mechanical controls are more important today than ever before. Weedsrob crop plants of water, air, light, and nutrients. Some weeds may even release substances that inhibit crop growth.

J. Some soils develop hardpans (compaction) and require deep tillage. This requires morephosphorus and potassium to build up fertility.

K. Row width, spacing of plants in the row, and number of plants per acre have importanteffects on yields.

L. Irrigation water can contain nitrate, sulfate, boron, potassium, bicarbonate, chlorine and other salts. A water analysis should be used to modify production practices for utilization of 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 the plants 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, showing stunted growth, unhealthy coloring of the leaves, and may be more prone to disease and insect problems.

A. Nutrients may become depleted by growing crops. Since crops are harvested, theorganic 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 thegrower to continually add the nutrients. The nutrients can sometimes be present in thegrowing medium, but they are not available for the plants to take up into their rootsbecause the pH level in the soil is not conducive to plant growth. Plants have differentpH requirements.

B. As a result, growers must add artificial fertilizers, manure, or other organic matter to the soil or nutrient solution for the plants to use. Soil or plant tissue tests should be conducted before fertilizers are added.1. A fertilizer is any material that is provided to plants to supply the nutrients neededfor plant growth. Fertilizers vary in the components they contain, the way they areapplied, and the function they serve.2. When choosing a fertilizer to use, one should always look for the fertilizer analysison 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, representthe percent of nitrogen, phosphorus, and potash, present in the fertilizer. So theexample above has 15% nitrogen, 10% phosphate, and 6% potash. Fillers are madeup of the remaining essential plant nutrients and are used to ensure a more evenapplication 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 afertilizer 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 determining an appropriate nutrient program based on your varying conditions.

D. Remember that high yields are not the only goal of a plant nutrition program, but thatoverall 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 green color. Although the atmosphere is 78% nitrogen gas, it is the most common nutrient deficiency seen in plants. N2 gas contains a triple bond which is extremely hard to break; this makes the molecule almost inert. Nitrogen fertilizer is expensive to produce and is thus an expensive input for farmers. Leguminous crops are able to use atmospheric nitrogen rather than rely on the application of fertilizer; this is an important factor in planning a sustainable agriculture 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 atany given time is found in the biomass or in dead organisms.1. Every nutrient that an organism uses is recycled throughout the ecosystem. Thesecycles are referred to as biogeochemical cycles. The water cycle is another wellknown

example of this process. The phosphorus and potassium cycles act in a similarmanner.2. The key concept is that no element is lost or consumed in the environment, butrather it changes form and moves between the abiotic and biotic components of theenvironment and is recycled.

B. Nitrogen is essential to all living organisms because of its use in the synthesis ofenzymes, proteins, and chromosomes. In plants, nitrogen is an important component ofchlorophyll.

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 itunavailable.2. The negative charge of nitrate causes it to easily leached away; this can become acause for water contamination. High nitrite levels in water can cause illness especiallyin children.3. Nitrogen that is absorbed by the plant is reduced toN2 -, NH- orNH2 which then issynthesized into more complex compounds and amino acids and proteins.4. Nitrogen assimilation is the incorporation of nitrogen into organic cell substancesby living organisms.

D. Most natural soil nitrogen is in the organic form meaning that it is combined in somemanner with carbon. Manures, decomposing organic matter, and urea are all forms oforganic 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 toan organic form. This process occurs naturally during initial decomposition or

nitrogen can be immobilized during chemical fertilizer composition to make itavailable to the plant at a later time.

E. Nitrogen fixation is the conversion of atmospheric nitrogen into oxidized forms that can be assimilated by plants.1. A symbiotic relationship that exists between bacteria and legume plants is utilized toconvert 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.3. Legumes such as beans, peas, alfalfa, clover, chickpea, and soybeans are able to takein the nitrogen through their roots. Legumes are plants that are members of the familyLeguminosae; they have the characteristic capability to fix atmospheric nitrogenin nodules on their roots with the aid of certain bacteria.4. Aquatic ferns and Gunnera macrophylla (tropical plant) form symbiotic relationshipswith blue-green algae to attain their nitrogen. Acacias, mesquites, alder, buckthorn,Casuarina, and paloverde plants also rely on bacteria. Lichens form a relationshipwith cyanobacteria which enables them to be one of the first organisms seen in primarysuccession. Cyanobacteria also aid the water fern Azolla and cycads.

5. Azotobacter, Beijerinckia, Klebsiella (some), Cyanobacteria (some), Clostridium (some), Desulfovibrio, Purple sulphur bacteria, Purple non-sulfur bacteria, and Green sulphur bacteria are free living nitrogen fixing organisms. Those that form symbiotic relationships with other organisms include Rhizobium, Frankia, and Azospirillum.a. All nitrogen fixing organisms are prokaryotes.b. Prokaryotes are one celled organisms that lack membrane bound organelles anda central nucleus.6. Rhizobia are aerobic bacteria that are naturally found in soils. They cause excessive

growth in the form of nodules on the cortex of the roots of legumes. Cortex is anouter layer of tissue in the roots of dicotyledonous plants located between the steleand epidermis.a. Rhizobia are autotrophic bacteria. Autotrophs are organisms that create theirown food rather than obtaining it from other organisms. They get their energyfrom the oxidation of mineral constituents, as well as carbohydrates from theirhost plant.b. The rhizobia and the plant live in a symbiotic relationship. Symbiosis is wheretwo dissimilar organisms live together in a mutually beneficial relationship.7. The soil bacteria enter the plant through openings in the root hairs and extend intothe cortex (outer cells) of the rootlets. This causes the growth of nodules to occurand is where nitrogen fixation occurs.8. The rhizobia “fix” atmospheric nitrogen (N2) by converting it to ammonia(NH4 +).a. Fixed is when a compound resists decomposition.b. Ammonia is then converted to nitrite (NO2 -) and then to nitrate (NO3 -). Thisprocess is known as nitrification.c. Nitrite is toxic to higher plants, but the conversion from nitrite to nitrate occursso quickly that no nitrite buildup in the soil or plant roots occurs.9. It appears that nitrogen, in the form of nitrate, is then diffused through the walls ofthe bacteria located in the root nodules and is absorbed by the host plant through thenodule root system.

F. To complete the nitrogen cycle, nitrogen can be removed from the soil by the uptake ofnitrogen by the plant, losses due to leaching, or by denitrification.1. Denitrification is when nitrates are converted to nitrogen gas.2. Denitrification occurs in soils that have no oxygen because of saturation from water;the nitrogen is then lost to the atmosphere.

G. Seeds are inoculated with rhizobia in order to increase the bacterial populations in thesoils of leguminous plants. Inoculation is the bulk treatment of leguminous seeds withrhizobia.1. Increased rhizobia populations will “fix” more nitrogen, making more nitrogenavailable to the plant.2. The increased supply of nitrogen by rhizobia lessens the need for supplementalnitrogen and generally increases the yield and quality of crops.3. However, these bacteria are crop-specific, with certain strains affecting only certaincrops.

H. Factors affecting rhizobium activity include:1. As soil temperature increases, soil bacteria become more active. This explains whynodules are not present in legumes during the winter months. Research has alsoshown that nodules slough off immediately after crop harvest, and then begin toreturn several days after harvest.2. Their populations are increased by soil moisture, soil oxygen, and soil aeration.3. A pH of 6.0–8.0 supports the greatest rhizobia populations.4. Also, the greater the exchangeable calcium in the soil, the greater the soil bacteriapopulations.

I. Nitrogen can also be added to the soil by lightning, application of commercial fertilizers, and through decomposition of dead organisms.

PLANT TISSUE TESTINGPart One: MatchingInstructions: Match the word with the correct definition.

a. atmospheric macronutrients e. incomplete fertilizer i. nitrogen fixationb. complete fertilizer f. legumes j. plant tissue testc. essential g. macronutrients k. soild. hydroponics h. micronutrients l. translocation

_______1. the process of turning atmospheric nitrogen into a usable form for plants by bacteria

_______2. nutrients needed in large quantities

_______3. a fertilizer that contains N, P, and K

_______4. nutrients needed in smaller quantities, but they are still essential

_______5. this term describes nutrients that plants must have in order to survive

_______6. these nutrients make up about 80–85% of the weight of a plant

_______7. a fertilizer that lacks any of the three primary elements

_______8. a method of growing plants in a nutrient solution

_______9. a test used to measure the amount of nutrients present in the sap of plants

______10. plants that use bacteria to obtain nitrogen from the atmosphere

______11. the outer portion of the Earth’s surface that supports plant growth

______12. the movement of organic molecules throughout plant tissues

Part Two: Fill-in-the-BlankInstructions: Complete the following statements.

1. __________________, ___________________, and ___________________ are examples of primary macronutrients.Illinois Biological Science Applications in Agriculture Lesson B3–3 • Page 162. ___________________, ___________________, and __________________ are considered secondary macronutrients.

3. __________________, _____________________, and ___________________ are atmospheric macronutrients.

Part Three: Multiple ChoiceInstructions: Circle the letter of the correct answer.

_______1. If a plant has yellow leaves, it is most likely deficient ina. nitrogenb. phosphorusc. potassiumd. none of the above

_______2. If a plant has burning in the leaf margins, lodging, and overall decreased quality, it most likely is deficient ina. nitrogenb. phosphorusc. potassiumd. none of the above

_______3. If a plant has stunted growth and purple leaves, it is most likely deficient ina. nitrogenb. phosphorusc. potassiumd. none of the above

_______4. If a plant experiences wilting, yellowing, and the leaves turn bronze, it is most likely deficient ina. nitrogenb. phosphorusc. potassiumd. none of the above

Part Four: Short Answer

Instructions: Answer the following questions.

1. Why do plant nutrient levels vary by stage of growth?

2. Why can sap from plant tissues be used to determine plant nutrient levels?Illinois Biological Science Applications in Agriculture Lesson B3–3 • Page 17

3. What is the purpose of nitrogen, phosphorus, and potassium in plants?

4. What factors affect the nutrient levels contained in plant tissues? Why?

5. Why is it important to study plant nutrition?Illinois Biological Science Applications in Agriculture Lesson B3–3 • Page 18AssessmentTS–A

Technical SupplementPLANT TISSUE TESTING1. How do plant nutrient levels vary by stage of growth? Why?The plant nutrients vary to accommodate the different stages of growth. For example,during cell division and protein synthesis, the plant needs higher amounts ofphosphorus and nitrogen. DNA has a phosphate backbone and nitrogen is alsoneeded in the formation of DNA. Phosphorus is also needed in ATP formation.ATP is needed for photosynthesis and other chemical reactions. Potassium isneeded for water retention and stomata functions. The demand for nutrients willdepend upon the stage of growth such as seedling, vegetative, or reproductive.

2. Why can sap from plant tissues be used to determine plant nutrient levels?The sap transfers the nutrients throughout the plant reflecting the gradient levels

and relative constitution in the plant. (This is much like how blood flows throughthe human body.)

3. Why are nitrogen, phosphorus, and potassium needed by plants?These three nutrients are absolute requirements for plants. The plant can synthesizesugars and fix carbon dioxide, but needs fixed nitrogen, potassium, and phosphorusin absorbable forms. Nitrogen is involved in the photosynthesis process because it isa component of chlorophyll. A deficiency of phosphorus results in stunted growthby preventing cell division. Potassium’s function is not completely known, however,it is an activator of many enzymes that are involved in the maintenance of thecorrect electrical potential of the plasmalemma (film membrane that surrounds thecell).Illinois Biological Science Applications in Agriculture Lesson B3–3 • Page 414. Why does additional nitrogen enhance the green color of leaves?Nitrogen aids in the plant’s production of chlorophyll. Adding extra nitrogenincreases the lushness of the plant. This is desirable for a crop like alfalfa, lettuce, orspinach where the leaves are the primary plant component being harvested. Addingnitrogen will also enhance the size and attractiveness of carrots, beets, sweet corn,peppers, eggplants, and celery; it does not improve their nutritive quality or flavor.Sometimes nitrogen can diminish the productivity of some crops by slowing thefruiting process. Excessive nitrogen for small grains increases the susceptibility forlodging, thus reducing photosynthetic efficiency and yield.

5. What factors affect the nutrient levels contained in plant tissues? Why?Factors that would affect nutrient levels are drought, changes in pH, salinity, temperatureshock, and flooding. Under stress conditions, nutrients become chelated in

the soil and are unavailable to the plant. For example, with flooding, nitrogenbecomes a limiting factor. Bacteria in the soil consume the nitrogen instead of makingit available to the plant. With low pH, phosphorus becomes insoluble in water;and potassium can become mobile, soluble, and easily leached.Illinois Biological Science Applications in Agriculture Lesson B3–3 • Page 42