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
Nutrients
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
+2and Mg
+
and vice versa
Average N – P - K Content of Horticultural
Plants
% 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
Applications
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
Fertilizer
Soil or Foliar Application
Kamas slide
Leaf Cuticle May Be a Barrier to Foliar Applications
Steps for Nutrient Entry Through the Leaf
Penetrate the cuticleMove through the apoplast
Absorption on membrane surface and transport into the leaf cells
Cuticle is a Major Limiting Factor to Entry
Stomata
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
Micronutrients
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
From
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
Effectively
Understand Elemental Chemistry and Mobility in Soils
Understand Nutrient Mobility in Plants
Kamas slide
Nutrient Mobility in Plants
Mobile
NitrogenPhosphorousPotassiumMagnesium
Nickel
Immobile
IronZinc
MolybdenumBoron
Calcium
Nutrient Mobility in Plants Is Primarily a Function of Their Solubility in Phloem Sap
Kamas slide
ModeratelyMobile
ManganeseCopper
What Elements Are Most Commonly Applied As
Fertilizers in Vineyards? Nitrogen
Phosphorous???
Potassium
Magnesium
Zinc
Iron
BoronKamas 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, UsuallyUrea +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
particles
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 CommentsP 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])
ChelatesKamas 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 Magnesium 0-0-22- 11[Mg]-22[S]
Muriate of Potash (Potassium Chloride 0-0-60)
Kamas slide
Band or Broadcast?
Nitrogen Typically Broadcast
Potassium/Magnesium Banded if Applied to Calcareous Soils
Kamas slide
Chelated Nutrients
Χηλή (chelè)
The bond between the organic chemical and theinorganic nutrient must be strong enough to protect
the nutrient, but must be weak enough to release thenutrient once it gets into the plant. In addition, the
chelating agent must not be harmful to plants. (Kamas slide)
Elements that Can Be Chelated
Iron
Zinc
Copper
Manganese
Calcium
Magnesium
CobaltKamas slide
There Are Many Products on the Market
Application Technology
Questions to Ask
Which Element is Deficient?
Length of Desired Effect?
Soil or Foliar? Element Mobility?
How Widespread is Problem?
What Chelating Agent is Called For?
Amount Needed? Economies of Scale Come
Into Play
When Are We Wasting Our Time
& Money? Trying to Apply Elemental
Forms of a Nutrient When Soil Conditions Impede Availability
Making Application After Damage is Done
Using Wrong Product for the Method/Point of Application
Using Products That Are Not Effective
Checks or Controls are a Major Key to Making Fertilizer Decisions
Just because your neighbor uses it does not mean it works
$1 or $2 per acre can add upHow can you recommend
when it MIGHT help
Do ..... Maintain a good soil/water
environment; avoid extremes Do a soil test every 3 to 5 years Avoid high amounts of
nutrients Use foliar fertilizer only to
correct micronutrients or in special situations
Top Related