Transcript Soil Colloids and Soil Chemistry

Fertilizer/ Fertigation Management
Section O
SWES 316
Fertilizing For Healthy Crops
Fertilizer Labeling
Fertilizer Grade
Is the percentage composition of fertilizer with
respect to N, P (as P2O5), and K (as K2O)
 For a fertilizer grade of 15-25-10
means the fertilizer is:

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
15% N
25% P2O5
(also called “available
phosphoric acid” or “phosphate”)
10% K2O
(also called “potash”)
Conversions
K2O to K:
K=39
K2=78
O=16
K2O=94
78/94=0.83
So K2O x 0.83 = K
P2O5 to P:
P=31
O=16
P2=62
O5=80
P2O5=142
62/142=0.44
So P2O5 x 0.44 = P
Factors to Consider

When choosing a fertilizer application method,
the following should be considered:
 Crop root zone
 Soil chemical/physical properties
 Fertilizer properties
 Nutrient mobility
 Soil Moisture
 Irrigation method, frequency
 System limitations
Placement Methods

Topdressing - Solids or liquids
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Broadcast
Band
Injection - Solids or liquids
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Called side-dressing when applied to growing
plants
Starter fertilizer is applied at planting time
Fertigation
 Foliar

Applying fertilizers in irrigated
systems:
1. Apply fertilizers either in the
area of maximum root density,
or where water will move it
toward roots.
2. Keep nutrients within crop
root zone, prevent leaching.
3. Consider nutrient mobility.
Broadcasting
 Things
to think about when broadcasting
fertilizer
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Best for soluble, mobile fertilizers
Results in a more or less uniform fertilizer
distribution
Band applications can be more efficient
nutrients are placed near root zone
because __________________________.
Do not broadcast NH4+ fertilizers on alkaline
soils unless immediately incorporating.
Broadcasting
Broadcast TSP followed
by “listing” (making beds)
Maricopa, AZ
Broadcasting Organic Fertilizer
Broadcasting
Slow-release fertilizer broadcast under
microsprinkler-irrigated navel orange,
Waddell, AZ
Broadcasting - gypsum and lime
are almost always broadcast
Gypsum broadcast on pecans,
Kansas Settlement, AZ
What can be broadcast?
 Solid
inorganic fertilizers
 Slow-release fertilizers
 Non-volatile liquid fertilizers
 Organic fertilizers
 Lime/gypsum
When is broadcasting appropriate?
When surface losses of NH3 are not likely.
 With highly soluble fertilizers when erosion
losses are not likely
 When soil disturbance is not desirable
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
Turf
No-till
Alfalfa
Permanent crops (apples, pecans, olives, etc.)
When treating bulk soil properties

Lime, gypsum
Band (injection) Application
Can be applied on or below (injection) the
surface. Useful for solids, liquids, or gases.
 Results in a localized zone of nutrient
distribution – good for nutrient tied up by soil.
 With at-planting applications, salt damage to
seedlings can be a problem.
 When side-dressing, root damage can occur.

Band Application
Surface band near transplanted
broccoli, sprinkler-irrigated
Oregon
“Side-dressing” lettuce with
liquid N fertilizer, Yuma
Band Application
http://www.yetterco.com/PressRelease/TheLea
dingEdge/2004-07-20/2004-07-20c.jpg
http://www.noble.org/Press_Release/Ag/Bandin
gFertilizer/PlacementTube.jpg
Band Application
Banded zinc application on pecan trees. Sahuarita, AZ
What can be band-applied?
 Solid
inorganic fertilizers (subsurface)
 Liquid fertilizers (surface or subsurface)
 Gas (NH3) must be applied subsurface
 Organics (some problems here)
When are band applications
appropriate?
 Almost
any time, except when root
disturbance would be excessive.
 Therefore, most appropriate in early
season before complete
development of root system.
 With immobile nutrients.
 Where nutrient losses or fixation are
likely.
Fertigation
 The
application of fertilizer with
irrigation water.
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Can be used with any irrigation method.
Will result in uniform or localized
nutrient distribution, depending on
irrigation method
Effectiveness of distribution depends on
irrigation uniformity
Water quality is important, especially in
drip systems!!!
Fertigation
Fertigation of liquid
N fertilizer onto
flood-irrigated durum
wheat
Maricopa, AZ
Fertigation
Fertigation can be applied in flood-irrigated
systems. Consider factors affecting efficiency.
Yuma
Fertigation to pasture, Washington state
Fertigation
Fertigation of citrus through
microsprinklers, Yuma
Fertigation through a subsurface
drip irrigation system.
Fertigation
Fertigation through pressurized irrigation systems
requires specialized equipment:
Water-powered
fertilizer pump
Venturi injectors
Consequences of Mixing
Incompatible Chemicals
H2SO4 + Ca(NO3)2 
CaSO4 + HNO3
CaSO4
If these chemicals were
improperly injected together
into an SDI system, plugging
of emitters and irreversible
damage would result.
What can be applied by fertigation?
 Most
liquid fertilizers
 Compatibility with irrigation water is of
the utmost importance in pressurized
(low-flow) irrigation systems.
 Efficiency of nutrient application will
depend upon efficiency of water
application.
http://www.fertilizer.org/ifa/publicat/html/pubman/IMAGES/fig7.gif
When is fertigation appropriate?
In irrigated systems
 In low-flow systems (i.e. drip or
microsprinkler) any time.
 In flood irrigation systems,
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fertigation is most appropriate later in the
season when root system is well-developed
fertigation is used with permanent crops
In greenhouses
Foliar Applications

Foliar applications are most useful for:
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Applications of micronutrients, especially to
alkaline soils
Applications at specific times (e.g. flowering)
It is difficult to apply enough N or K through
a foliar application to supply plant needs
without burning.
 Nutrient concentrations in liquid should be
<1-2% to prevent burning.

Foliar Fertilization
Foliar Fertilization
Plants are easily damaged by
foliar applications - damage from
cytokinins in foliar seaweed
fertilizer on ginseng.
http://www.omafra.gov.on.ca/english/crops/hort/
news/hortmatt/2005/12hrt05a3.htm
Timing of Fertilization

Preplant
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At-planting
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Can be topdressed, with or without incorporation, or
injected.
soil test
Should be based on a preplant _____________.
Usually injected with or near the seed
“Pop-up” or “starter” application
Post-planting
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Usually injected or fertigated, can be topdressed
“Side-dressing”
Pre-plant Fertilization
 Best
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for:
Applications of P and/or K in the event
of low soil test values
Applications of NH4-N in the event of a
low soil test value (not too far in
advance)
-
Can cause salt damage
Special Case - Band applications at
planting
“Starter”
fertilizer often
applied “2x2”
Placed with
seed is called
“pop-up”
At-planting Fertilization

“Pop-up” fertilizers are applied with the seed.
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“Starter” fertilizers are usually applied a short
distance from the seed
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Amounts of N and K (highly soluble fertilizers)
should be limited to prevent seedling damage
Less danger from salt damage
Excellent way to ensure good seedling vigor
Fluid Journal, Fall 2001
Fluid Journal, Spring 1997
Fluid Journal, Summer 1999
Damage from Banded Fertilizer
Fertilizer Salt Index
Materials and analysis
Salt Index
per equal weights of
materials
per unit of
nutrients1
Nitrogen/Sulfur
Ammonia, 82%N
Ammonium nitrate, 34%N
Ammonium sulfate, 21%N, 24%S
Ammonium thiosulfate, 12%N, 26%S
Urea, 46%N
UAN, 28%N (39% NH4NO3, 31% urea)
32%N (44% NH4NO3, 35% urea)
47.1
104.0
68.3
90.4
74.4
63.0
71.1
0.572
3.059
3.252
7.533
1.618
2.250
2.221
20.0
29.2
26.7
0.455
0.456
0.405
1.6132
1.7542
8.4
120.1
42.6
68.0
0.097
1.936
0.852
2.720
Phosphorus
APP, 10%N, 34%P2O5
DAP, 18%N, 46%P2O5
MAP, 11%N, 52%P2O5
Phosphoric acid, 54%P2O5
72%P2O5
Potassium
Monopotassium phosphate, 52%P2O5, 35%K2O
Potassium chloride, 62%K2O
Potassium sulfate, 50%K2O, 18%S
Potassium thiosulfate, 25%K2O, 17%S
1One unit equals 20 lb
2Salt index per 100 lbs of H PO
3
4
Fluid Journal Spring 2001
Post-planting Fertilization
Ability to do this is limited by crop
characteristics and equipment.
 Fertigation is the best way to do this, but is
only possible in irrigated systems
tissue tests
 Should be guided by ________________
.
