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

• 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.

• 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

• 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.

• 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

• 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.

• 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.

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