Understanding Fertilizer Material

There is great variety among fertilizer materials. In general, fertilizers fall within two major categories: commercial fertilizer sources and organic sources. While it is difficult to make direct comparisons between these two sources, a few loose comparisons can be made.

First, commercial sources are typically high analysis fertilizers, while organic sources are low analysis. This means that commercial fertilizers contain a larger percentage of a given nutrient than organic sources. As a result, commercial fertilizers are applied in lesser amounts than organic sources, since it take less commercial fertilizers to achieve a given rate.

Secondly, composition of organic fertilizer is generally much more varied than commercial fertilizers. This lack of consistency can make it difficult to predict how much organic fertilizers should be applied in order to obtain a desired rate.

Thirdly, commercial fertilizer production is fossil fuel intensive. As a result, the price of commercial fertilizer can be relatively expensive.

Commercial fertilizer sources

NITROGEN FERTILIZERS

Anhydrous ammonium is the starting block for most inorganic nitrogen fertilizers. Anhydrous ammonium is manufactured by reacting N2 with H2 under extreme heat and pressure in the presence of a catalyst, known as the Haber-Bosch technology. The Haber-Bosch technology requires large energy input, but allows for the manufacture of high N analysis fertilizers.

Anhydrous Ammonium

• Anhydrous ammonium has the highest nitrogen analysis out of all inorganic fertilizers
• It is comprised of 82% nitrogen.
• It must be kept under pressure since it evaporates under normal atmospheric pressure.
• It is very harmful to human tissue, such as eyes, skin, and lungs. Thus, there are many safety precautions associated with the handling of NH3.

Ammonium sulfate

• Contains 21% nitrogen and 11% sulfur
• Sugarcane and pineapple production
• Ammonium sulfate is acid forming and lowers soil pH.

Ammonium phosphate

Monoammonium phosphate (MAP)

• 11-18% nitrogen and 48-55% P2O5
• MAP is a water soluble fertilizer
• The soil pH temporarily lowers to about 3.5 in areas where MAP initially reacts with soil.

Diammonium phosphate (DAP)

• 18-21% nitrogen and 46-53% P2O5
• DAP is a water soluble fertilizer.
• The soil pH temporarily reduces to 8.5 in areas where DAP initially reacts with soil.
• DAP may produce free ammonia in high pH soils, which may cause seed injury if placed too close to seed rows.

Potassium nitrate

• 13% nitrogen and 44% K2O
• Provides soil with readily available nitrate, which generally increases soil pH.

Calcium nitrate

• 15% nitrogen and 34% CaO
• Provides soil with readily available nitrate.
• However, calcium nitrate is hygroscopic (absorbs moisture from air) and must be kept under air-tight storage conditions.

Urea

• 45-46% nitrogen
• Advantages of urea over other nitrogen sources include:
  • reduced caking of fertilizer material
  • less corrosion on equipment
  • decreased costs associated with storage, transportation, and handling
• Once applied to the soil, an enzyme known as urease transforms urea to NH4+ and HCO3-.
  • This transformation readily occurs under warm, moist conditions.
• Urea temporarily increases the pH of the soil it contacts, due to the initial release of NH3. However, the soil pH may ultimately decrease as the NH4+ nitrifies to NO3-, which is an acid producing reaction.
• In soils with high pH, NH4+ may volatilize and escape from the soil in the form of NH3. Volatilization losses are reduced by incorporating or washing urea into the soil.
• Urea can contain biurate, which is phytotoxic to most plants.
  • Although most plants tolerate up to 2% biurate levels, pineapple and citrus are sensitive to biuret. The urea should contain less than 0.25% biuret.

Sulfur-coated urea

• 22-38% nitrogen and 12-22% sulfur
• Sulfur-coated urea is a controlled release fertilizer.
  • It contains a coat of sulfur that surrounds a urea granule, which controls its release.
  • Urea is only released after the sulfur coat is oxidized by microorganisms.
  • The rate at which urea becomes available depends on the thickness of the sulfur coat.
• Sulfur coated urea is advantageous in coarse textured soils and/or soils that have a great nitrate leaching potential.

PHOSPHATE

The major source of inorganic phosphorus fertilizers is rock phosphate. Rock phosphate is a naturally occurring mineral, which is mined from the earth. Deposits of rock phosphate occur around the world, such as in the United States, Russia, Morocco, and China.

Rock phosphate (RP)

• 27-41% P2O5 and 25% Calcium
• The minerals that make up RP are various forms of apatite. The reactivity of RP depends on the type of apatite and its inherent purity. RP is not water soluble and only becomes available to plants under acidic conditions. RP is most reactive when it is finely ground and incorporated into warm, moist, acidic soils with long growing seasons. Although the availability of RP is slow, it has a great long term residual effect.

Superphosphate

Single superphosphate (SSP)

• 16-22% P2O5, 11-12% sulfur, and 20% calcium
• SSP is manufactured by reacting RP with sulfuric acid.
• SSP does not have a great influence on soil pH.

Triple superphosphate (TSP)

• 44-52% P2O5, 1-1.5% sulfur, and 13% Ca
• TSP is produced by treating RP with phosphoric acid
• Like SSP, TSP does not have a great effect on soil pH.

Ammonium phosphate

Monoammonium phosphate (MAP)

• 11-13% N, 48-62% P2O5, and 0-2% S
• MAP is water soluble.
• MAP temporarily lowers the soil pH to 3.5 in areas where MAP initially reacts with the soil.

Diammonium phosphate (DAP)

• 18-21% N, 46-53% P2O5, and 0-2% S
• DAP are water soluble.
• The soil pH temporarily lowers to 8.5 in areas where DAP initially reacts.
• DAP may produce free NH3 in soils with a high pH, which may cause seed injury if placed close to seed rows.

POTASSIUM

Potassium is mined from the earth as soluble potassium salts, or potash, with varying degree of purity. Canada is home to the world’s largest potash deposit.

Potassium chloride (muiate of potash)

• 60-63% K2O
• KCl is the most commonly used K fertilizer.
• KCl readily dissolves in water

Potassium sulfate (sulfate of potash)

• 50-53% K2O, 17% S K2SO4-
• Potassium sulfate is completely water soluble.
• In comparison to KCl, potassium sulfate:
  • has a lower salt index
  • may be used on crops that are sensitive to Cl- (i.e. avocado).

Potassium nitrate

• 44% K2O and 13% N
• Potassium nitrate is also water soluble.
• Increases soil pH
• Potassium nitrate is also a source of nitrogen.

Potassium-magnesium sulfate

• 22% K2O, 11% Mg, and 22% S
• This inorganic fertilizer does not have a significant effect on soil pH

CALCIUM

Lime

• Soil amendment which is commonly used to raise the pH of the soil.
• Ground coral in Hawaii contains 38% Mg and 0.6% Mg

Calcium Carbonate

• Approximately 38% Ca, depending upon its source
• A common liming material, calcium carbonate also supplies calcium to the soil.

Dolomite

• 22% Ca and 12% Mg, depending upon the dolomite source
• In addition to raising the pH, dolomite is a source of calcium and magnesium.

Gypsum

• 23% Ca and 19% S
• Unlike liming materials, gypsum does not increase the soil pH.
• In addition to providing calcium and sulfur, gypsum may be used to correct soil physical problems and/or aluminum toxicities.

Calcium nitrate

• 15% N and 20% Ca
• Calcium nitrate is very soluble in water.

Superphosphates

Single (SSP)

• 18-21% Ca
• SSP supplies both calcium and phosphate.

Triple (TSP)

• 12-14% Ca
• Like SSP, TSP supplies both calcium and phosphate

MAGNESIUM

Dolomite

• 22% Ca and 12% Mg, depending upon the source
• Dolomite is a source of both Ca and Mg, in addition to its liming affect.

Magnesium sulfate (Epsom salt)

• 9.8% Mg and12% S
• Epsom salt is very soluble and does not alter soil pH.

Magnesium oxide

• 55% Mg
• Magnesium oxide increases soil pH.
• It is not highly water soluble. For maximum reactivity, it is often mixed into the soil.

SULFUR

Elemental sulfur

• In its elemental form, sulfur is a solid
• Elemental sulfur is insoluble in water.
• When finely-ground elemental sulfur is incorporated into the soil, microorganisms oxidize and convert it to sulfate.
  • The finer the sulfur, the greater its oxidization potential when incorporated into the soil.

Ammonium sulfate

• Contains 24% S and 21% N
• Ammonium sulfate can have a strong acidifying effect on soil

MICRONUTRIENT

Iron

• Iron (ferrous) sulfate
  • Contains19% Fe
  • May be used as a foliar spray to correct Fe deficiencies
• Iron chelate (iron EDTA)
  • Contains 5-14% Fe
  • May be used as foliar spray or directly applied to the soil
  • Though expensive, chelates prevent the formation of insoluble Fe compounds

Zinc

• Zinc sulfate
  • Contains 35% Zn
  • Due to its low soil mobility, zinc sulfate should be mixed into the soil when broadcasted
  • Band placement is favorable in finely textures soils that are low in Zn
  • Available as a foliar spray
• Zinc chelate (EDTA)
  • Contains 14% Zn
  • May be applied as a foliage spray or directly to the soil
  • Zn chelates are very soluble and may be incorporated into liquid fertilizers

Copper

• Copper sulfate
  • Contains 25% Cu
  • May be applied to the soil and/or foliage
  • Incorporating Cu into the plant root zone increases the efficiency of Cu
• Copper chelate (EDTA)
  • Contains 13% Cu
  • Very soluble
  • May be applied as a foliar spray

Manganese

• Mangenese sulfate
  • Contains 26-28% Mn
  • May be applied as a foliar spray and/or directly to the soil in a band application
• Manganese chelate (EDTA)
  • Contains 5-12%
  • Not recommended as a broadcast

Boron

• Sodium borate, or borax
  • Contains 11% B
  • May be applied to soil as a band or broadcast
  • Available as a foliar spray
  • Since boron has a small sufficiency range, it should be mixed uniformly into the soil
  • Care should be taken to prevent B toxicity.
• Sodium tetraborate
  • Contains14-15%
  • Most widely used B fertilizer

Granusol

• A manufactured product that contains 5.4% Fe, 5.2% Zn, 5.6% Mn, 5.4% Mg, 2.6% Cu, and 0.5% B. Since it is largely insoluble, it should be incorporated into the soil.

Blends (Mixed Fertilizers)

There are many available inorganic fertilizers that contain various combinations of N, P, and K fertilizers. If a particular formulation of N, P, and K is desired, a blend can conveniently meet the needs of the farmer or gardener, while reducing the costs associated with buying and applying multiple fertilizers.

Fertilizer Calculations

When applying fertilizers to your field or garden, you will add fertilizers at a specific rate of application. To accomplish this goal, it is necessary that you can perform two calculations:

• First, you must know how to determine the percentage of nutrients, particularly N, P, and K, that a particular fertilizer contains.
• Secondly, you must know how to calculate the quantity of fertilizer that must be added to a given area in order to achieve the recommended rate of fertilization for a particular nutrient.

The following provides a detailed explanation of how to perform these calculations, which was prepared and written by Jay Deputy of Tropical Plants and Soil Science.

Fertilizer Application Calculations

The major nutrients

A complete fertilizer contains all three of the major nutrient elements nitrogen (N), phosphorus (P), and potassium (K).
The total percentage of the nutrients contained in a fertilizer is given as three numbers, which together is known as the analysis. These numbers are usually in large print on the front of the container or bag. An example would be 10-30-10.

Nitrogen (N)

Nitrogen is reported as total N and may take one of three chemical forms:

• NO₃^– or nitrate-N
• NH₄ or ammonium-N
• Urea-N

Most fertilizers contain a mixture of two or all three of these N forms.

The percent of total-N is represented by the first of the three analysis numbers. For example, a bag with an analysis of 10-30-10 contains 10% N by weight of all nitrogen forms. Therefore, a 50 pound bag of 10-30-10 contains 5 pounds of total-N, which accounts for 10% of the bag’s 50 pounds weight.

Calculation of %N: 10% of 50 pounds = (.10 x 50 pounds) = 5 pounds of total N

Phosphorus (P)

Phosphorus is never present as pure elemental P. Instead, P is reported in fertilizers as the chemical compound P₂O₅ or ortho-phosphate. The percent of P₂O₅ in a complete fertilizer is represented by the second of the three analysis numbers. For example, a bag with the analysis of 10-30-10 contains 30% P₂O₅ by weight. Therefore, a 50 pound bag of 10-30-10 contains 15 pounds of P₂O₅.

Calculation of % P₂O₅: 30% x 50 pounds = (.30 x 50 pounds) = 15 pounds of P₂O₅

However, notice that the above calculation determines the amount of P₂O₅ in the bag of fertilizer, rather than the amount of total P. To report the quantity of total P, the percent of elemental, or pure, P must be determined.

To calculate elemental P, we must determine the percent by weight of P in P₂O₅, which is 44%. Thus, 44% of P₂O₅ is elemental P. To convert the percent of P₂O₅ to percent elemental P, multiply the percent P₂O₅ by 44%.

Therefore, a bag of 10-30-10 contains 15 pounds of P₂O₅ (see above calculation) and 6.6 pounds elemental P (15 pounds P₂O₅ x .44 = 6.6 pounds P)

Calculation of % P = % P₂O₅ x 44% = 15 pounds P₂O₅ (see above calculation) x .44 = 6.6 pounds of P

Potassium (K)

Potassium is also never present as pure elemental K, but is reported as its oxide form of K₂O, commonly called potash. The percent of K₂O in a bag of blended fertilizer is represented by the third of the three numbers of the analysis. For example, a bag of fertilizer with an analysis of 10-30-10 contains 10% K₂O by weight. Therefore, a 50 pound bag of 10-30-10 contains 5 pounds of K₂O 10% of 50 pounds.

Calculation of % K₂O = 10% of 50 pounds = (.10,x 50) = 5 pounds of K₂O

As with P, in some cases potassium is reported as percent elemental (or pure) K. To calculate elemental K, we must determine what percentage (by weight) of K₂O is elemental K, which we know to be 83%. This means that 83% of K₂O is elemental K. To convert percent K₂O to percent elemental K, multiply the percent K₂O by 83%.

Therefore, a bag of 10-30-10 contains 5 pounds of K₂O (see above calculation) and 4.15 pounds elemental K

Calculation of % K = % K₂O x 83% = 5 pounds K₂O x .83 = 4.15 pounds elemental K

Calculating fertilizer application rates

The recommended amount of fertilizer to be applied to a crop at any one time has been experimentally determined for the major nutrients. In most cases, the most essential nutrient under consideration is nitrogen. In the case of turfgrass nutrition, the recommended amount of fertilizer per application is given in terms of pounds of nitrogen per acre or per 1000 square feet. The normal recommended rate for turf is one pound N per 1000 sq. ft. The frequency of applications will vary with the species of turfgrass.

In order to calculate the total amount of fertilizer being applied at any one time, several things need to be considered. These are:

• Recommended rate in terms of pounds of N per 1000 square foot.
• The analysis of the fertilizer being used. (The quantity of N that the fertilizer contains, which is indicated by the first number of the analysis.) Keep in mind — the lower the N %, the more fertilizer that will be required.
• The total area being fertilized.
• Must be mathematically calculated depending upon the overall shape of the plot

Once these have been determined, the following calculation will give the total amount of fertilizer needed to cover the designated area.
(Rate of N / 1000 sq. ft) X (Area in sq. ft) / (% N in fertilizer) = Pounds of fertilizer

Remember that when working with percentage figures, convert to a decimal before calculating. Therefore, convert 33% N to .33 for the calculation

Example 1 
Using a fertilizer with analysis 33-5-5 at a rate of one pound N/1000 ft2, how much fertilizer is required to cover a turf plot that measurers 100 ft x 50 ft.
First calculate the area of the plot,
area = L x W 100 x 50 = 5000 ft2
(Rate of N / 1000 sq. ft) X (Area in sq. ft) / (% N in fertilizer) = Pounds of fertilizer

Example 2 
(1 lb /1000 sq ft) X 5000 sq. ft / .33 = 15.15 lb of 33-5-5 fertilizer
This time use a different fertilizer, 20-5-10 at the same rate on the same plot of turf
(1 lb /1000 sq ft) X 5000 sq. ft / .20 = 25 lb of 20-5-10 to cover the same area

Why the difference?

33-5-5 contains more N per pound of fertilizer, and therefore, requires less material to provide one pound of N / 1000 ft2. However, this is not the only criteria that should be used in deciding what analysis to use. The nitrogen formulation is often a more important consideration.

Organic sources

Proper maintenance of soil organic matter is an important part of nutrient management, as increasingly supported by the scientific community. Organic matter enhances both chemical and biological soil properties, as well as supplying sources as macro- and micronutrients. The most stable form of organic matter—humus—plays an all-important role in improving soil structure, nutrient retention, and water storage. Additionally, it has been shown that additions of animal and green manures, as well as compost, enriched microbial diversity and populations.

NITROGEN

Animal manure

The amount of nitrogen that manure provides and its subsequent availability to plants is influenced by a several factors:

• Nutrient analysis of the animal feed
• Storage and handling procedures of the manure
• Amount and type of materials added to the manure
• Timing and method of application
• Properties of the soil
• Choice of crop

Nitrogen Analysis

• Manures can contain between 0.5 and 6% total nitrogen, though typical values range from 0.5 to 1.5%.
• Of the total nitrogen, approximately only 25% to 50% is in the form of ammonium and directly available to plants./li>
• The remaining 50-75% is organic nitrogen and must be mineralized before it is utilized by plants. Thus, the same conditions for optimal mineralization of organic matter are the same for the optimal mineralization of organic nitrogen in manure.

Organic Nitrogen

Organic nitrogen is further divided into two categories:

• unstable organic nitrogen
• stable organic nitrogen

Unstable organic nitrogen

• urea or uric acid are the primary forms of unstable organic nitrogen
• mineralization into ammonium occurs rapidly
• highly vulnerable to volatilization and denitrification losses
• it is recommended that manure be incorporated into the soil to prevent nitrogen losses to the atmosphere

Stable organic nitrogen

• mineralizes at much slower rates than the unstable fraction
• the stable nitrogen that is less resistant to decomposition (approximately 30% to 60% of the total nitrogen) mineralizes during the first year of application
• the stable nitrogen that is more resistant to decomposition mineralizes during the following years with declining rates of mineralization each year that passes

The following table contains nutrient analysis information for various types of animal manures and composts.

Table 9. Nutrient Composition of Various Types of Animal Manure and Compost (all values are on a fresh weight basis).

Manure Type	Dry Matter	Ammonium-N	Total Na	P2O5	K2O
	%	————————- lb/ton —————————
Swine, no bedding	18	6	10	9	8
Swine, with bedding	18	5	6	7	7
Beef, no bedding	52	7	21	14	23
Beef, with bedding	50	8	21	18	26
Dairy, no bedding	18	4	9	4	10
Dairy, with bedding	21	5	9	4	10
Sheep, no bedding	28	5	18	11	26
Sheep, with bedding	28	5	14	9	25
Poultry, no litter	45	26	33	48	34
Poultry, with litter	75	36	56	45	34
Turkey, no litter	22	17	27	20	17
Turkey, with litter	29	13	20	16	13
Horse, with bedding	46	4	14	4	14
Poultry compost	45	1	17	39	23
Dairy compost	45	<1	12	12	26
Mixed compost: Dairy/Swine/Poultry	43	<1	11	11	10

^aTotal N = Ammonium-N plus organic N 
Sources: Livestock Waste Facilities Handbook, 2nd ed., 1985, Midwest Plan Service; Organic Soil Amendments and Fertilizers, 1992, Univ. of Calif. #21505.

Legume /green manure

A particular advantage of implementing a legume/green manure rotation into the soil/cropping system is the added source of organic matter. However, green manures also improve soil structure by reducing bulk density. Green manures are generally grown for less than a growing season and are plowed under before producing seeds. Examples of common green manure crops are sunnhemp, annual ryegrass, sudangrass, sudex, and sesbania. Legumes, such as sunnhemp and sudex, are particularly beneficial since they are nitrogen fixing species and are a good source of nitrogen.

Management of organic matter also helps to reduce the occurrence of soil erosion, thus improving soil conservation. In addition to rotations of green manures, cover crops, companion plantings, mulching, and stripcropping with grass species can help minimize the depletion of soil resources, as well as providing a good source of organic residue on the soil surface.

Sewage sludge

• Sewage sludge consists of the solid products formed during sewage treatment
• It is not uniform in mineral composition
• Generally, it contains less than 1 to 3% total nitrogen

PHOSPHORUS

Animal manure

• Animal can contain 0.1 to 0.4% phosphorus.
• Like nitrogen, the amount of phosphorus in animal manure depends upon several factors, including type of animal feed, handling, and storage of manure.
• Out of the total amount of phosphorus in fresh manure, approximately 30 to 70% is organic. Thus, mineralization must occur before the organic phosphorus becomes available to plants.

Sewage sludge

• Sewage sludge contains approximately 2 to 4 % total phosphorus.

Microbial Phosphorus

• Certain bacteria in the soil are capable of increasing the availability of phosphate, by increasing its solubility.
• The most abundant P-solubilizer is Bacillus spp.

POTASSIUM

Manures

• Potassium content may range between 0.2 and 2% in manures.

Sewage sludge

• Potassium primarily exists as soluble, inorganic K+.

SULFUR

• Animal manure and Sewage sludge: 0.2-1.5%

CALCIUM

• Animal and municipal wastes: 2-5% (dry)

MAGNESIUM

• Animal and municipal wastes: 0.2-1.5%

MICRONUTRIENTS

Animal wastes and municipal wastes

Fe: 0.02% – 0.1% (benefit increased chelation)
Zn: 0.01-0.05%, municipal (up to 0.5%) (benefit chelation)
Cu: Animal small (0.002-0.03%), municipal (0,1%) (natural chelation)
Mn: animal (0.01-0.05%) municipal (0.05%) (chelation)
B: animal (0.001-0.005%) municipal (0.01%) (chelation)
Cl: most low because Cl is highly soluble and mobile
Mo: animal (0.0001-0.0005%) municipal (0.0001%)

Distinctions between manure fertilizers and commercial fertilizers

• Nutrient analysis: While commercial fertilizers may have a relatively high analysis of the major macronutrients (nitrogen, phosphorus and potassium), the nutrient content of manures is much less.
  • As a result, a larger quantity of manure must be applied to the soil as compared to the addition of commercial fertilizer at an equivalent rate. It may take up to 30 tons of manure per acre to achieve the desired nutrition.
• The nutrient content of manure fertilizers is highly variable.
  • Factors that affect nutrient content include animal type and diet, handling, storage, and water content.
  • Chicken manure generally contains more nitrogen, but also quickly decomposes and subsequently releases ammonia.
  • Since manure is an organic source, the availability of nutrients is also largely influenced by the biological processes of mineralization and immobilization.

BENEFITS AND DISADVANTAGES OF MANURE FERTILIZERS

Benefits

• Provides a source of ammonium
• Increases the availability of certain essential elements, including phosphorus and various micronutrients
• Increases the mobility of phosphorus and micronutrients in the soil
• Increases soil organic matter content
• Improves water holding capacity
• Increases water infiltration rates
• Improves soil structure
• Reduces aluminum toxicity
• Recycles nutrients

Disadvantages

• Contains variable nutrient analysis
• Requires high rates of application due to lower analysis (especially N)
• Variable quality
• Undergoes variable rates of mineralization, therefore difficult to predict nutrient availability
• Less flexibility involved in applying specific nutrient combinations
• Risk of nitrogen losses volatilization during handling and placement
• High costs associated with transportation
• Has relatively low nutrient content per unit weight as compared to mineral fertilizers
• Potential weed problem through the transfer of weedy seeds which can be minimized through composting

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