Soil organic matter (OM) decomposes to release nutrients (primarily N, P, and S), which are mineralized.  In addition, OM can retain cations in available forms, depending on the CEC.

Commercial fertilizer is recommended only when other nutrient sources insufficiently supply nutrients to the crops.  It provides nutrients in available forms (soluble, exchangeable cations or adsorbed anions), which provide for current and subsequent crops.

Soil minerals dissolve over time, and along with OM help to increase (CEC, cation exchange capacity), allowing for the retention of plant-available nutrients.

Animal manures, composts, and sludges provide readily-plant available nutrients (P and K) and also release nutrients as they decompose (N and S).  In addition, some animal wastes may contain high metal levels (for instance, Cu).  Sludges, which may include urban or industrial waste, contain variable nutrient levels (C:N ratio) and may have high metal content.

Plant residues release nutrients back to the soil through decomposition and through leaching of soluble nutrients.  Residue coverage of the soil can furthermore result in moisture conservation, indirectly influencing plant nutrients available.

Compost application (image source)

1. Anhydrous ammonia: NH₃
• Fertilizer grade: 82-0-0
• Fertilizer with the highest analysis of N
• Stored as a liquid under pressure
• Injected in the soil as a gas
• Highly caustic: requires use of protective equipment, and subject to regulations (use, transport, etc)
2. Urea: (NH₂)₂CO
• Fertilizer grade: 46-0-0
• Soluble, readily available N source
• Dry fertilizer product
• Contains the highest percentage of N for all dry fertilizers
• Significant N losses as volatilization of NH₃ may occur when surface applied
• Hygroscopic: absorbs water from the air
• Can cause high pH near seeds
• Can potentially cause salt toxicity
3. Ammonium nitrate: NH₄NO₃
• Fertilizer grade: 34-0-0
• Physical form: solid or liquid
• Hygroscopic: absorbs water from the air
• Can cause salt toxicity
4. Urea ammonium nitrate solution (UAN): Urea + NH₄NO₃
• Fertilizer grade: 28-0-0 to 32-0-0
• Soluble, readily available N source
• Liquid fertilizer product made by dissolving urea and ammonium nitrate in water
• Urea portion is subject to NH₃ volatilization
5. Ammonium sulfate: (NH₄) ₂SO₄
• Fertilizer grade: 21-0-0-24S
• Contains 24% Sulfur
• Soluble, readily available source of N and S
• Dry fertilizer productNH₃ volatilization is not a concern unless applied to high pH soils (>7.5)
• Reduces soil pH
• Mild; low salt toxicity potential

1. Rock phosphate: Ca(H₂PO₄)₂
• Fertilizer grade: 0-18-0
• Physical form: solid
• Generally very insoluble
2. Triple superphosphate: Ca(H₂PO₄)₂
• Fertilizer grade: 0-46-0
• Physical form: solid
• Acidifying agent
• Water-soluble
3. Monoammonium phosphate: NH₄H₂PO₄
• Fertilizer grade: 11-52-0
• Physical form: solid
• Soluble, readily available source of P & N
• Most common dry P fertilizer in NNY
• May create an acidic zone around fertilizer granules
4. Diammonium phosphate: (NH₄)₂H₂PO₄
• Fertilizer grade: 18-46-0
• Physical form: solid
• Soluble, readily available source of P & N
• Initial soil reaction can produce free NH₃ (high pH, basic) which can cause seedling injury if too much is placed near the seed
5. Ammonium polyphosphate: Ca(NH₄H₂PO₄)₂
• Fertilizer grade:  10-34-0 or 11-37-0
• Physical form: liquid
• Soluble, readily available source of P and N
• Popular source for starter fertilizer

1. Potassium chloride: KCl
• Fertilizer grade: Contains 60-63% K₂O
• Physical form: solid
• Most abundantly used potassium fertilizer
• Often referred to as Muriate of Potash
• Water soluble source of K
2. Potassium sulfate: K₂SO₄
• Fertilizer grade: 50% K₂O
• Physical form: solid
3. Potassium nitrate: KNO₃
• Fertilizer grade: contains about 13% N, 44% K₂O
• Physical form: solid
4. Potassium magnesium sulfate: K₂SO₄•MgSO₄
• Contains about 22% K₂O, 11% Mg, 22% S
• Physical form: solid, water-soluble
• Good source of Mg and S
• Often referred to as Sul-Po-Mag or K-Mag

1. Calcitic lime: calcium carbonate, CaCO₃
• Fertilizer grade: 32% Ca
• Physical form: solid
2. Dolomitic lime: calcium magnesium carbonate, CaMg(CO₃)₂
• Fertilizer grade: 22% Ca
• Physical form: solid
3. Gypsum: calcium sulfate, CaSO₄
• Fertilizer grade: 18-23% Ca, 15-19% S
• Physical form: solid
4. Potassium magnesium sulfate: K₂SO₄•MgSO₄
• Fertilizer grade: 22% K₂O, 11% Mg, 22% S
• Physical form: solid, water-soluble
• Good source of Mg and S
• Often referred to as Sul-Po-Mag or K-Mag
5. Lime: also burned lime, quicklime, calcium oxide: CaO
• Physical form: solid
6. Hydrated or slaked lime: calcium hydroxide, Ca(OH)₂
• Fertilizer grade: 46% Ca
• Physical form: solid

Nutrient use efficiency is the yield output per unit input (e.g. bushels of corn per lb of applied N).

Total availability is the total amount of a nutrient that is eventually expected to become plant available.  It should be noted that this could be extended over many years.

Water solubility reflects the portion of the fertilizer that dissolves in water (and is thus more immediately available).

Guaranteed analysis is the minimum amount of N, P₂O₅, K₂O, etc. in the fertilizer material.  The Association of American Plant Food Control Officials (AAPFCO) writes rules, definitions, and labeling standards for fertilizer industry.  States then have laws for guaranteed analysis, sales and distribution.  In New York, see Section 10 of Ag and Markets Law.

The salt effect of a fertilizer reflects the amount of soluble salts in the soil solution, in direct contact with roots.  High soluble salt content (which can result from high applications of N as ammonium salts, K sources, etc.) can cause seedling damage through dehydration.

Total Kjeldahl Nitrogen is the total N analytical method that determines the organic and ammonium N fraction in soils, plants, and waters.  Soils range from 0.05 to 0.3% typically, but can be much higher for mucks.  Plants are normally 0.2 to 4% depending on species, age, plant part, etc.

Organic N is the nitrogen fraction that is organically-bound (i.e. protein).  Organic N is not water-soluble and is slow to become available.  Most manure and biosolid N is organically-bound, and must undergo mineralization before it can be used by plants.

Inorganic N is not organically-bound; for instance, ammonium, urea, nitrate, and nitrite.

Organic P is organically-bound phosphorus.  Like organic N, it is not water-soluble and must mineralize before it becomes available.  Most organic P is found as phytate.

Inorganic P is not associated with carbon; usually P dissolved in solution, such as PO₄^3-, HPO₄^2-, and H₂PO₄^-.  Most P in manure and biosolids is in this form.

Dissolved P is found in the soil solution, as PO₄^3-, HPO₄^2-, and H₂PO₄^-.

Particulate P is attached to soil particles.

Before using any fertilizers, it is important to understand how to read a fertilizer label.  All fertilizers are labeled as %N - % P₂O₅ - %K₂O.

• For example, a fertilizer labeled as a 20-5-10 means that the product contains, by weight: 20 percent N, 5 percent P₂O₅, and 10 percent K₂O.

The nature of the fertilizer (liquid or dry) must also be taken into account.  Generally there is no measurable difference in crop response, as long as they supply the same amount of soluble nutrient.  From a plant's perspective, a pound of N from urea is equal to a pound of N from UAN.  The agronomic differences among N fertilizers are the risk for N losses due to volatilization, denitrification and leaching.  Ultimately, the choice between wet and dry P fertilizers is based on economics and farmer preference.  Note that for liquid fertilizers where the rate is given in gallons per acre, the density of the fertilizer must be known to determine the amount of nutrients applied per acre.  For example:

Material                         Weight (lbs/gal)

10-34-0                                     11.7

9-18-9                                      11.7

28-0-0                                      10.7

Fertilizer blends are developed by combining basic fertilizers to get nutrient concentrations appropriate for a given crop, soil, or application method.  Some common blends include:

• Solid

20-10-10                        8-32-16 20-20-20

6-24-24 10-20-20           0-10-40

5-15-15                          0-20-20 19-19-19

• Liquid

21-17-0 10-34-0 7-21-7

The basic formula for calculating how much fertilizer to apply to a given area for a specific amount of nutrient is:

Fertilizer "rate" often refers to two things:

1. The desired lbs of actual nutrient per acre
• e.g. a crop nutrient goal of 100 lbs N/acre, 25 lbs P₂O₅/acre, and 50 lbs K₂O /acre
2. The desired lbs of fertilizer material per acre necessary to achieve the lbs of nutrient per acre goal
• e.g. given a 20-10-0 fertilizer, how many lbs of fertilizer material do we need to apply 25 lb N/acre?  How much P₂O₅ and K₂O tag along?

Manure is a readily-available byproduct of livestock operations, and contains many nutrients that are essential to plants.  Manure contains several N pools, which can be separated into two main categories:

1. Ammonium N (may be listed as "inorganic N" on manure reports), or "fast N"
2. Organic N, or "slow N"

These pools behave differently in terms of N release for plant growth.  Ammonium N is readily-available, while organic N is less available and may take months or years to become available.  Thus, when calculating manure application rates, you must take into account the manure applied in prior years.

Although concepts of N availability over time are accepted in all states in the Northeast, actual N credits might differ from state to state.  Refer to Land Grant University guidance for state-specific recommendations.

Decay series for stable organic N in manure vary by animal type.  To determine the amount of N that will be available to the present crop, you must account for the N from the application of the present crop plus any residual N that will be available from manure applications in recent past years.  The table below provides the factors to estimate the N from the present application and from past applications.  The "present year" factor would be taken times the amount of organic N applied in the present year.  A "last year" factor of 12% indicates that an estimated 12 % of the organic N applied in the manure last year is expected to be utilized by the present crop (a year after application).  Therefore this factor would be taken times the amount of organic N applied in the manure last year.  A similar calculation would be done if manure was applied two years ago.

Cornell guidance for manure organic N release by animal type (Klausner, 1997, derived from work by Klausner et al., 1994

Comparison of manure incorporation methods (image source) 

Manure broadcast without incorporation (image source)

Injection of manure (image source)

Injection is used to place liquid or gaseous fertilizer below the soil near plant roots.

• Advantages: reduce losses through precise application of nutrients
• Disadvantages: slow, expensive (requires specialized equipment.

UAN application (image source)

Surface broadcast is a method by which fertilizer is applied on the surface across an entire field. High capacity fertilizer spreaders are often used which spin dry fertilizer or spray liquid fertilizer on the soil surface or on a growing crop.

• Advantages: fast, economical
• Disadvantages: high nutrient losses, low uniformity
• P efficiency is only 1/3 to ¼ that of banding

Broadcast incorporated improves on the efficiency of surface application by incorporating fertilizer through plowing or disking.  Plowing is considered better in terms of nutrient availability, as it creates a nutrient-rich zone a few inches below soil surface (where developing plant roots can absorb it).

• Advantages: reduces losses compared to broadcast, improves plant uptake
• Disadvantages: slow, non-uniform application, erosion risk

Band application is also known as starter application.  Fertilizer is applied in bands near where developing roots will easily reach it; either to the side and below the seed rows, slightly below the seeds, or in between rows.  A common practice is to band fertilizer 2 inches to the side and 2 inches deeper than the seeds or plants.  This provides the plants with a concentrated zone of nutrients and can improve nutrient use efficiency.  The process can be done before or simultaneous with planting or seed drilling.  Liquid or dry fertilizers can be used.

• Advantages: high nutrient use efficiency, jump-starts early growth.  Many fields are deficient in P, due to soil binding and cold temperatures.  Banding P makes it easier for plants to grow.  It also slows NH₄⁺ conversion to NO₃^- (nitrification), reducing the risk of leaching.
• Disadvantages: costly, slow; risk of salt burn to plants

Fertigation is distribution with water-soluble fertilizers and chemicals through an irrigation system.

• Advantages: high nutrient use efficiency
• Disadvantages: irrigation equipment needed (injection pump, etc); risk of uneven application in windy situations

Foliar application is application of a small amount of fertilizer or mineral through direct spraying onto the leaves.

• Advantages: rapid uptake
• Disadvantages: phytotoxicity, high expense, limited to small and/or repeated application

Sidedressing is when fertilizer is applied between rows of young plants to provide a boost during periods of rapid growth and nutrient uptake.  The most common use is sidedressing N on corn plants.  Application amount is dependent on the results of a Pre-Sidedress Nitrate Test (PSNT) done when corn plants are 12-24 inches tall.

• There are three methods of sidedressing:

1. UAN applied with a pesticide sprayer fitted with drip nozzles
2. UAN injected between corn rows with disc openers
3. Anhydrous ammonia injected into soil

• Advantages: high nutrient use efficiency
• Disadvantages: timing often falls during the wet and busy season; slow process

Topdressing is when fertilizer or manure is spread on established fields (grasses, legumes).

• Advantages: high nutrient use efficiency
• Disadvantages: losses likely.

Topdressing N on winter wheat (photo courtesy of Bill Cox, (image source))

Seed placement is also known as pop-up application.  A small amount of fertilizer is placed with corn seeds during planting, sometimes in conjunction with banding.  Both liquid and dry can be used.

• Advantages: lower equipment costs, starter effect greater than just meeting nutrient requirements

• Disadvantages: can be phytotoxic if too much fertilizer is applied; retro-fitting planters can be expensive.  Urea and DAP cannot be used, and to prevent salt burn the total rate must be kept below 10 lbs of N + K₂O.

There are numerous organic fertilization products available.  For complete references and information, the appropriate certification agency should be contacted.  For a list of some organic certified soil amendments, see the following:

• http://omri.org/OMRI_datatable.php
• http://www.baystateorganic.org/locateproducts.html
• http://www.baystateorganic.org/docs/Baystate%20List%20of%20local%20products%20May%202009.doc
• http://attra.ncat.org/organic.html

• Starter fertilizer selection combines many issues.
• The composition of applied fertilizers should be based on the fertility status of the whole farm.  The only way to really know the status is to have a full set of soil samples!
• We can no longer ignore manure nutrient contributions, especially those that accumulate in the soil year after year.
• We can no longer guess at soil fertility any more than we guess at forage samples – we now have the ability to make more informed decisions based on soil samples and other data.
• Use fertilizer imports to SUPPLEMENT, not SUBSTITUTE for on-farm nutrients.