Fertilizer/ Fertigation Management
Section O
SWES 316
Fertilizing For Healthy Crops
Fertilizer Labeling
Nitrogen
Phosphorus
Potassium
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: 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 P2=62
O=16 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 Broadcast Band
Injection - Solids or liquids 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 Best for soluble, mobile fertilizers Results in a more or less uniform fertilizer
distribution Band applications can be more efficient
because __________________________. Do not broadcast NH4
+ fertilizers on alkaline soils unless immediately incorporating.
nutrients are placed near root zone
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
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.noble.org/Press_Release/Ag/BandingFertilizer/PlacementTube.jpg
http://www.yetterco.com/PressRelease/TheLeadingEdge/2004-07-20/2004-07-
20c.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. 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:
Venturi injectors
Water-powered fertilizer pump
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,
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:
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
http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2005/12hrt05a3.htm
Plants are easily damaged by foliar applications -
damage from cytokinins in foliar seaweed fertilizer on
ginseng.
Preplant Can be topdressed, with or without incorporation, or
injected. Should be based on a preplant _____________.
At-planting Usually injected with or near the seed “Pop-up” or “starter” application
Post-planting Usually injected or fertigated, can be topdressed “Side-dressing”
Timing of Fertilization
soil test
Pre-plant Fertilization Best 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
Placed with
seed is called
“pop-up”
“Starter”
fertilizer often
applied “2x2”
At-planting Fertilization
“Pop-up” fertilizers are applied with the seed. Amounts of N and K (highly soluble fertilizers)
should be limited to prevent seedling damage “Starter” fertilizers are usually applied a short
distance from the seed 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
Fluid Journal Spring 2001
Materials and analysisSalt Index
per equal weights of materials
per unit of nutrients1
Nitrogen/SulfurAmmonia, 82%N 47.1 0.572Ammonium nitrate, 34%N 104.0 3.059Ammonium sulfate, 21%N, 24%S 68.3 3.252Ammonium thiosulfate, 12%N, 26%S 90.4 7.533Urea, 46%N 74.4 1.618UAN, 28%N (39% NH4NO3, 31% urea) 63.0 2.250 32%N (44% NH4NO3, 35% urea) 71.1 2.221
PhosphorusAPP, 10%N, 34%P2O5 20.0 0.455DAP, 18%N, 46%P2O5 29.2 0.456MAP, 11%N, 52%P2O5 26.7 0.405Phosphoric acid, 54%P2O5 1.6132
72%P2O5 1.7542
PotassiumMonopotassium phosphate, 52%P2O5, 35%K2O 8.4 0.097Potassium chloride, 62%K2O 120.1 1.936Potassium sulfate, 50%K2O, 18%S 42.6 0.852Potassium thiosulfate, 25%K2O, 17%S 68.0 2.7201One unit equals 20 lb 2Salt index per 100 lbs of H3PO4
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
Should be guided by ________________ . tissue tests
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