CPT Unit 4

• Fertilizers


  Any substance that is added to the soil or applied to plants, to supply the elements essential for plant nutrition
• Types of fertilizers


  • Organic
  • Inorganic
  • Minerals
  • Synthetic
• Organic fertilizers


  • Derived from plant matter, animal excreta, sewage and food waste
  • Generally in the form of animal manure, green manure, and biosolids
  • Slow release
  • Low nutrient content
• Mineral fertilizers


  • Produced from materials mined from naturally occurring nutrient deposits or nitrogen fixation
  • Contain the three macro-elements (Nitrogen, phosphorus, and potassium)
  • Fertilizer industries transform millions of tons of air, natural gas, and mined ores into NPK plant fertilizers
  • Potassium and phosphorus fertilizers are produced in chemical processes of purification of mined minerals
• Inorganic/Synthetic fertilizers


  • Man-made chemical compounds that contain one or more primary nutrients
  • May be in liquid or granular form
  • Provide immediate results, unlike organic fertilizers
  • High nutrient content
  • Urea is synthetic but in organic form
• Granular fertilizers


  • Dry fertilizers that are converted into granules and are mixed frequently to obtain the desired proportion of nutrients
  • The method allows farmers to check the amount of NPK added to the fields
  • Cheaper in bulk
  • Easier to store
  • More effective for heavy applications before plantation
  • Slow-release
• Liquid fertilizers


  • Can be applied to the soil as well as the plants and are called leaf applications
  • Nutrients are more readily available for immediate use
  • Leaf application allows a farmer to make mid-season corrections to add important nutrients to plants
  • Can be applied through leaves or on the ground
  • Easy mixing, can be with pesticides
• Slow-release fertilizers


  • Provide plants with nutrients over a longer period
  • Offers a sustainable and continuous supply of N for up to 4 months
  • Excellent for fast coloring plants
  • Accelerate growth
  • Plants do not have any nutrients at their disposal
  • Slow-release fertilizers are leached out much less often
• Fast-release/ Quick-release Fertilizers


  • Fast fertilizers are powder plant nutrients mixed with water according to the manufacturer's label
  • Also known as water-soluble fertilizers
  • They are readily available after application
  • Rapid release into the soil can wash out environmentally harmful nutrients
  • It only takes two or four weeks
• Nitrogen


  • It is a key building block of chlorophyll responsible for photosynthesis
  • It is also involved in the production of proteins, enzymes, nucleic acids, and amino acids
  • Nitrogen-fixing bacteria in the soil can convert atmospheric nitrogen into usable forms, enriching the soil
• Phosphorus


  It promotes early root growth, winter hardiness, and seed formation, stimulates tillering, and increases water use efficiency
• Potassium


  • It is essential for photosynthesis, protein synthesis, enzyme activation, and osmoregulation
  • Prevents diseases and lessens the effects of excessive nitrogen application
• Excessive NPK can damage crops and plants
• A balance of these nutrients is essential, according to the plants' needs
• Ammonia (NH3)


  • Nitrogen is converted into ammonia via the Haber-Bosch process
  • It is a pressurized liquid in the storage tank
• Diammonium Phosphate (NH4)2HPO4


  • More concentrated
  • Provide complete phosphorus nutrition through crop growth and development and an initial dose of nitrogen and low sulfur content
• Ammonium nitrate (NH4NO3)


  • It is an odorless, almost colorless crystalline salt
  • Improves plant growth and ensures a clear supply of nitrogen from which plants can extract
  • Dissolve quickly in water to release nitrogen into the soil
• Ammonium sulfate ((NH4)2SO4)


  Useful when nitrogen and sulfur are needed
• Urea (NH2CONH2)


  • The most important nitrogen fertilizer on the market (46% of N)
  • It is a white organic chemical compound
  • It has a neutral pH and is suitable for almost all types of soil
  • It provides nitrogen to plants to promote green leaf growth
  • Due to the high concentration of nitrogen, it must be mixed with soil or sand before application
• Single superphosphate [Ca(H2PO4)2]


  • Made from finely ground rock phosphate mixed with concentrated sulfuric acid
  • SSP is grey to brown, granules with easy storage
  • Contains 17-20% P2O5 and 16% S
  • Not suitable for highly acidic soils
• Triple superphosphate (TSP)


  • 44-52% P2O5
  • Powdered TSP tends to cake, but granulated TSP is free-flowing
  • Contains less sulfur compared to SSP
• Dicalcium phosphate (CaHPO4)


  • High production cost, inconvenient handling, and application of its powder form
  • Made by reacting rock phosphate with hydrochloric acid and adding lime to produce a precipitate
  • Contains about 35% P2O5
  • Effective phosphorus source for long-term crops (sugarcane or crops of acidic soils)
• Rock phosphate


  • It is light grey to brown and neutral in nature
  • Finely ground for direct application
  • Contains 29-37% of P2O5
  • Slow-acting phosphorus fertilizer
  • Utilized best in soils with a pH <5.5 or soils rich in organic matter
• Potassium chloride (KCl)


  • Usually called Muriate of potash (MOP) and widely used K fertilizer
  • Low cost and contains more K, 50-52% (60-63% ) and 45-47% for Cl-
  • Spread over the soil surface before growing and planting
  • Placed on the side of the seed to avoid damaging the seedling
• Potassium sulfate ()


  Rarely found in pure form, rather naturally mixed with salts containing Mg, Na, and Cl, respectively
• Potassium nitrate ()


  • Soluble source of two essential nutrients for plants
  • Applied to the soil before the growing season or as a supplement during the growing season
• Potassium magnesium sulfate ()

  • Provides an immediately available supply of K, Mg, and S for growing plants
  • Due to the economy, the delivery rate can be based on the need for Mg, S, or both
• Chelates


  • Improves micronutrients such as Fe, Mn, Zn, and Cu, which oxidize or precipitate easily in soil; therefore, the application of chelates increases these micronutrients' efficiency
  • Chelated micronutrients are protected from oxidation, precipitation, and immobilization, where a large molecule called a ligand or chelator surrounds the micronutrient ions
  • Contributes to the productivity and profitability of commercial crop production
• Ethylenediaminetetraacetate (EDTA)


  Commonly found in synthetic fertilizers and not absorbed by the plant
• Diethylenetriamine pentaacetate (DTPA)


  Suitable for pH levels soils
• Ethylenediamine dihydroxy-phenylacetic acid (EDDHA)


  Superior synthetic chelating agent, expensive (production-wise)
• How to choose the right fertilizer

  1. Identify the type of soil, whether it is sandy, clayey, or loamy

  2. Check the pH level of the soil (acid or alkaline)

  3. Look for any nutrient deficiencies in the soil that may be hindering plant growth

  4. Research the specific nutrient requirements for the crops you are growing

  5. Identify the essential macronutrients and micronutrients required

  6. Consider the growth rate of your crops, as nutrient requirements may vary during different stages

  7. Weigh the advantages and limitations of the fertilizer
• Fertilizer ratio


  • N-P-K ratio, the proportion of Nitrogen (N), phosphorus (P), and potassium (K), determined by dividing each of the three numbers in the fertilizer grade by the lowest number in the grade
  • E.g., 16-16-16 means 16% nitrogen, 16% phosphorus, and 16 % potassium, ratio is 1-1-1
  • Phosphate and potash may be expressed as their elemental forms, P and K, or as their oxide forms, P2O5 and K2O. Nitrogen is expressed as N
  • All fertilizers contain at least one of these components; if not, the ratio of this nutrient is zero. E.g., 12-0-0 contains nitrogen only (the ratio is 1-0-0)
• Fertilizer grade


  • The minimum guaranteed percentage of total N, available P2O5, and water-soluble K2O, in that order, in a fertilizer material
  • It is useful in determining application rates
  • Calculated on a % of total weight basis
• Fertilizer grade


  • 4:3:4(33)
  • 4 parts N, 3 parts P, 4 parts K, total plant food concentration is 33%
• Calculating elemental concentrations from fertilizer grade

  1. The concentration of N: 4/11 X 33 = 12%

  2. The concentration of P: 3/11 X 33 = 9%

  3. The concentration of K: 4/11 X 33 = 12%
• 1. P-K ratio


  The minimum guaranteed percentage of total N, available P2O5, and water-soluble K2O, in that order, in a fertilizer material
• Fertilizer grade


  The minimum guaranteed percentage of total N, available P2O5, and water-soluble K2O, in that order, in a fertilizer material
• In South Africa, NPK products are named using a numerical system, e.g., 4:3:4(33), which is called the "grade" of the product
• Total plant food concentration

  The total percentage of nutrients (usually of N, P, K, and S) in a fertilizer material