Fertilizer/ Fertigation Management

Section OSWES 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=62O=16 O5=80

P2O5=142 62/142=0.44So 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