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Transcript of Fertilizers - Aggie Horticulture · PDF file sound production program. What is a Fertilizer?...

  • Fertilizers

    Larry A. Stein

    Professor and Extension Horticulturist

    Texas A & M AgriLife Extension

    Uvalde, Texas

  • Fertilizers

    Not miracle products

    Nutrition is just one of the components of a sound production program

  • What is a Fertilizer?

    Fertilizer is any material of natural or synthetic origin that is applied to soils or to plant tissues (usually leaves) to supply one or more plant

    nutrients essential to the growth of plants. (Kamas slide)

  • Well Drained Soil

    50% soil

    50% pore space

    ½ pore space has H2O

    ½ pore space has air

  • Oxygen is needed for:

     Respiration – breakdown of sugar and release of energy

     Absorption – Active transport across cell membrane

     Plant hormone production

     Exclude toxic ions

  • Fertilizers are Salts

    Varies with the type

    Too much – water moves out of the plant and burns the leaves

  • The Only Reason Fertilizers Work is Because of Water

     Moves into the root zone

     Root zone to root

     Higher [ ] to lower [ ]

     Nutrient deficiencies can be water deficiencies

  • Only New Growing Root Tips Absorb Water and


    Requires oxygen

    Top 3-6 inches of the soil

  • Excessive Fertilization Can Cause

    Too much vigor

    Delayed ripening – too much N

    Leaf chlorosis – P ties up iron and zinc

  • Balance is the Key to Nutrition Management as Ions Compete

    with Each Other

    Too much K +

    can affect uptake of CA

    +2 and Mg


    and vice versa

  • Average N – P - K Content of Horticultural


    % N % P % K

    Ornamentals 2.0 – 6.0 0.2 – 0.7 1.5 – 3.5

    Fruits 2.0 – 7.2 0.15 – 0.3 1.0 – 2.5

    Vegetables 2.4 – 5.6 0.3 – 0.7 1.5 – 4.0

    Generally a 3-1-2 ratio

  • In Order to Get the Most Out of Fertilization


    Need to know which elements to apply based on soil test and crop

    Timely applications

    Accurate placement

  • Soil Type Will Dictate Frequency

    of Applications

  • Foliar Fertilizers

    Impossible to supply a significant portion of the macronutrient needs of most plants with foliar fertilizers

  • Micronutrient Vs. Macronutrients

     Application Method Dictated by Amount Needed

     Availability May Be Limited by Soil pH  Will Dictate Form of


     Soil or Foliar Application

    Kamas slide

  • Leaf Cuticle May Be a Barrier to Foliar Applications

  • Steps for Nutrient Entry Through the Leaf

    Penetrate the cuticle Move through the apoplast

    Absorption on membrane surface and transport into the leaf cells

  • Cuticle is a Major Limiting Factor to Entry


    Vein areas

    Very young leaves

    Base of trichomes

  • Key Role in Absorption is

    Keeping the droplet wet for a long period of time

    Not surfactants

  • Foliar Fertilizers Are Best Used To Supply


  • Foliar Nitrogen Fertilization

    • Remember, Nitrogen is a MACRO Nutrient

    • May Make Sense in the Fall to Simply Maintain a Healthy Canopy

    • Feed Grade Urea

    – 5 lbs. per 100 gallons

    Kamas slide

  • Soil pH

    -Log [H+]

    high pH = high Ca = tie-up of Fe and Zn

  • Nutrient Availability

  • Organic or Inorganic Sources?

     It Does Not Matter to a Plant What Source the Nutrient Comes


     There Can Be Down Sides to Long Term Use of Synthetic Fertilizers  Fertilizers are Salts  Failing to Add Organic Matter Back to Soils

    Will Cause a Reduction in Soil Structure

     There Can Be Down Sides to Use Of Manures  Weed Seeds  Salts

     Composts?  Content???  Cost of Product and Cost of Application (Kamas slide)

  • In Order to Understand Fertilizers and How to Use The


     Understand Elemental Chemistry and Mobility in Soils

     Understand Nutrient Mobility in Plants

    Kamas slide

  • Nutrient Mobility in Plants


    Nitrogen Phosphorous Potassium Magnesium



    Iron Zinc

    Molybdenum Boron


    Nutrient Mobility in Plants Is Primarily a Function of Their Solubility in Phloem Sap

    Kamas slide

    Moderately Mobile

    Manganese Copper

  • What Elements Are Most Commonly Applied As

    Fertilizers in Vineyards?  Nitrogen

     Phosphorous???

     Potassium

     Magnesium

     Zinc

     Iron

     Boron Kamas slide

  • Critical Characteristics of Nitrogen

    • Very Mobile in Soils (neg. charge)

    • Very Mobile in Plants

    • Soils Typically Very Low in Nitrogen

    • Native Nitrogen in Soils Consists of:

    – Complex, Insoluble Unavailable Organic Compounds

    – Simple, More Soluble, Available Compounds in Soil Solution

    Kamas slide

  • Nitrogen

    Usually deficient

    Plant available forms;

    Usually NO3 - (nitrate)

    Some NH4 + (ammonium)

  • Material %N Comments

    Urea 46 Volatile Dry (NH2-CO-NH2) Material

    Ammonium Nitrate 34 Dry Material (NH4NO3) Less Volatile

    Ammonium Sulfate 21 Volatile on High (NH4)2SO4 pH soils

    Nitrogen Solutions (UAN) 28-32 Volatile, Usually Urea +NH4NO3 + water Injected in Drip

    Practical Nitrogen Sources

  • Soil Cations and Anions

    Cations are Positively Charged (+) Anions are Negatively Charged (-)

    Kamas slide

  • NH4 + not mobile because

    it is a cation; + charges are attracted to soil


  • NO3 - can leach because it

    is an anion - charges not attracted to soil particles

  • Denitrification

    Conversion of NO3 -

    to N2 gas

    Occurs under low oxygen conditions

    O.M. + NO3 - CO2 + H2O + N2

  • Volatilization of Ammonia

     Soil ph > 7.5

     Broadcast

     Wet Soils

  • Percent Nitrogen in each fertilizer

     Ammonium sulfate ( 21 %)

     100 pounds ammonium sulfate = 21 pounds N

  • Percent Nitrogen in each fertilizer

     Ammonium nitrate (33 %)

     100 pounds ammonium nitrate = 33 pounds of nitrogen

  • Percent nitrogen in each fertilizer

     Urea (45 %)

     100 pounds of urea = 45 pounds of nitrogen

  • Percent nitrogen in each fertilizer

     N – 32 (32 %)

     One gallon of N – 32 weighs 11.08 pounds/gal.

     Only 32 % N; 11.08 X 0.32 % = 3.55pounds N/gal

     ½ from urea; ½ from ammonium nitrate

     ¼ = ammonic; ¼ = nitrate; ½ = urea

  • Nitrogen Additions

     Late Fall/Early Winter- Source? Wet Fall?

     5”-10” Shoot Growth- Broadcast if Rain Likely

     Mid Summer- Apply Through Drip

     Foliar Applications- Late Summer/Early Fall if Needed (feed grade urea@ 5#/100 gallons of water)

  • Manures - Be Cautious • Little Control on

    Nitrogen Availability to the Vines

    • Weed Seed Contamination?

    • Potential High Salt Content

    Kamas slide

  • Situations to Avoid

    • High Nitrogen Applications in Vineyards Still At Risk From Frost

    • Excessive N Status at Bloom

    – Shatter

    – Poor Flower Bud Initiation

    Kamas slide

  • Phosphorous

     Literature Cites Grapevine Phosphorous Deficiency Only in Very Low pH Soils

     Phosphorous Moves Extremely Slowly in Soils, So if Needed Should Be Added Pre- Plant

     Added After Planting, Must Be Disked in Where the Roots Used To Be

  • Fertilizer %N Avail Sol Equiv Salt Comments P acid K Acidity Index

  • Magnesium/Potassium

     Competition for Uptake Between Ca, Mg and K

     Petiole Values are Only Reliable Way to Balance Needs

    Kamas slide

  • Sources of Mg

     Dolomitic Lime on Acid Sites

    (Calcium, Magnesium Carbonate)

     Sul-Po-Mag

    (Sulfate of Magnesium Potassium

    0-0-22-22 [Mg]-18[S])

     Kmag (Langbeinite ) Organic Form of Sulfate of Potash Magnesium

     0-0-22- 11[Mg]-22[S]

     Epsom Salts

    (Magnesium Sulfate 0-0-0-10[Mg])

     Chelates Kamas slide

  • Sources of Potassium

     Sul-Po-Mag

    (Sulfate of Magnesium Potassium

    0-0-22-22 [Mg]-18[S])

     Kmag (Langbeinite ) Organic Form of Sulfate of Potash Magn