This Unit is about Phosphorus.


Phosphorus is a chemical element with symbol P and atomic number 15. As an element, phosphorus exists in two major forms—white phosphorus and red phosphorus—but due to its high reactivity, phosphorus is never found as a free element on Earth. Instead phosphorus-containing minerals are almost always present in their maximally oxidised state, as inorganic phosphate rocks.

Sources of phosphorus

  • Soil organic matter e.g. crop residues.
  • Weathering of rocks that contain phosphate e.g. Tororo Rock.
  • Organic manures e.g. farm yard manure and from artificial fertilizers.

Importance of phosphates

  1. It stimulates root development and Nidule formation legumes.
  2. Promotes respiration in plant cells, accelerates the breakdown of carbohydrates as well as other metabolic processes.
  3. It helps information of proteins and fats.
  4. It is necessary in reproductive process e.g. flowering food and seed formation etc.
  5. It promotes cell division and early plant maturity.
  6. It encourages leaf formation and the development of mono shoots.
  7. It impacts disease resistance to certain crops.
  8. It makes straw in cereal crops strong therefore prevents lodging of crops.
  9. It improves crop quality especially the vegetables.

Ways through which phosphorus can be lost from the soil.

  • It can be taken up by crops which are later harvested.
  • Fixed by iron and aluminum oxided and this very common in clay soils.
  • In very acidic soils phosphorus becomes unavailable to plants.

Deficiency symptoms of phosphorus.

  1. Stunted growth
  2. Lack f branching in roots and stems.
  3. Leaves especially maize become purpled and fall off prematurely.
  4. Low yield of grain fruits and food crops and delayed maturity.

Excessive symptoms of phosphorus.

Excess phosphorus induces iron deficiency of iron.

Practical control of phosphate availability.

  • Phosporus is not very soluble in water so only about 5-20% of the phosphorus.
  • Addition of agriculture lime to keep the PH between 6 & 6.5 this will prevent phosphorus being fixed.
  • Crop residues should be in cooperated in the soil and organic manure added.
  • Phosporus fertilizers should applied as pellets to reduce its reaction with soil.


ASSIGNMENT : PHOSPORUS assignment MARKS : 10  DURATION : 1 week, 3 days

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