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Inorganic Fertilizers | Agriculture Form 2

Welcome to our form two agriculture digital content.

Agriculture is an important subject in our day to day life. In form one you were introduced to both crop and livestock practices. In form two you will continue broadening the content scope using the following topics:-

Inorganic fertilizers, Planting crop plants, Nursery practices, Field practices, Vegetables production, Livestock parasites, Introduction to livestock health and Livestock nutrition.

You will also have the opportunity to practice some hands on skills in answering examination questions as a preparation for the subject evaluation. Welcome and enjoy all the activities in form two agriculture digital content.

Suggested Practical Activities in use of Inorganic Fertilizer

Learners to plant a twelve cabbages seeds in a selected containers. After two weeks of growing seedlings are selected for the following treatments.

a)To the 1st two seedlings, supply all the nutrients except nitrogen.
b)To the 2nd two seedling ,supply all the nutrients except phosphorus
c) To the next two seedling ,supply all the nutrients except potassium
d) To all other seedlings ,supply all the nutrients required.
Observe the growth habits of the crops for the next two weeks as shown below.

Measure the length ,width and height of the stems on different days after the above treatments.

Background to Inorganic Fertilizers

There are various ways through which soil loses fertility.

Let us remind ourselves some of these ways:

  • Leaching,
  • Soil erosion,
  • Monocropping,
  • Continuous cropping,
  • Burning.

Soil erosion

Soil fertility may be maintained through methods such as:

  • Manuring,
  • Control of soil erosion,
  • Mulching,
  • Weed control,
  • Irrigation,
  • Drainage,
  • Crop rotation,
  • Soil pH control.

Inorganic Fertilizers Glossary

1.Soil Fertility
Is the ability of the soil to supply all the essential elements to plants in their correct proportions.

2.Essential elements
Are nutrients required by plants for normal plant growth.

Are nutrients required by plants in large quantities.

Are nutrients required by plants in small quantities.

5.Soil sampling
Is the taking of some soil from a piece of land which is a representative of the whole land.

6.Soil testing
Is the process of analyzing the soil samples.

7.Soil PH
Is a measure of acidity or alkalinity of the soil solution.

Is a process through which dissolved nutrients move downwards with infiltrating water beyond the root zone of most crops.

Inorganic Fertilizers

Topic Objectives.

By the end of this topic, you should be able to:

a) list the essential elements,
b) classify the essential elements,
c) state the role of each macro-nutrient,
d) describe the deficiency symptoms of the macro-nutrients,
e) identify and classify fertilizers,
f) describe the properties of various fertilizers,
g) describe soil sampling and testing procedures,
h) use appropriate methods of fertilizer application,
I) calculate fertilizer application rates,
j) explain how soil acidity and alkalinity affect crop production.

Soil Fertility II (Inorganic Fertilizers)


Soil fertility is the ability of the soil to supply all the essential elements to plants in their correct proportions. In this topic we are going to cover:

  • Essential elements
  • Inorganic fertilizers
  • Soil sampling
  • Soil testing

    Inorganic Fertilizers

    Essential elements
    Essential elements are nutrients needed by plants for normal plant growth. Lost nutrients can be replaced through application of fertilizers.
    Essential elements are in two categories, namely
    macronutrients and micronutrients.

    The macronutrients are required by plants in large quantities.
    Macronutrients include: Nitrogen, Phosphorous, Potassium, Magnesium, Sulphur, Calcium, Hydrogen, Oxygen and Carbon.

    The micronutrients are required by plants in relatively small quantities.
    Micronutrients include: Molybdenum, Chlorine, Manganese, Zinc, Copper, Iron and Boron.

    Roles of Nitrogen in crops

    • Helps in protein formation
    • Forms part of chlorophyll molecule
    • Encourages vegetative growth
    • Increases size of cereal grains
    • Regulates the availability of phosphorous and potassium to plants

    Take note of the yellow leaves in maize as a result of leaf chlorosis due Nitrogen deficiency.

    Role of phosphorous in crops

    • Formation and establishment of roots
    • Helps in metabolic processes
    • Helps in cell division
    • Quickens ripening of fruits
    • Helps in flowering, fruit formation and seed formation
    • Strengthens plant skeleton structure

    Observe the purple colour of leaves on kale crop showing phosphorous deficiency.

    Role of potassium in crops

    • Helps in carbohydrate formation and translocation
    • Assists in uptake of nitrates from the soil
    • Imparts resistance to crops against diseases
    • Strengthens straws of cereals
    • Helps in development and formation of chlorophyll
    • Helps in neutralization of organic acids
    • Helps in plant metabolism
    • Balances the effects of nitrogen and phosphorous

    Observe keenly the leaf curling and yellowing of leaf on the cabbage crop.

    Roles of magnesium in crops

    i) Forms part of the chlorophyll molecule.
    ii) Aids carbohydrate metabolism.
    iii) Helps in oil formation on some legumes.
    iv) Promotes nitrogen fixation in legumes.
    Deficiency symptoms of magnesium in cabbage plant

    Observe the purple, orange and red patches of colour on the leaves.

    Roles of sulphur in crops

    (i)Helps in formation of plant proteins
    (ii)Helps in formation of plant hormones
    (iii)Helps in formation and activation of certain enzymes.
    (iv)Influences certain physiological processes in plants.

    Few nodules are observed on the roots when beans lack adequate sulphur.

    Roles of calcium in crop production

    (i)Strengthens plant cell walls
    (ii)Helps in protein synthesis
    (iii)Helps in cell division
    (iv)Raises soil pH of acidic soils
    (v)Promotes formation of soil aggregates
    (vi)Makes phosphorous and potassium more readily available in the soil

    Observe the water soaked blossom ends of fruits due to calcium deficiency in young fruits.

    Macronutrients exist in ionic forms when dissolved in water.

    Observe NO3-, K+, Mg2+ and Ca2+ being absorbed in ionic forms. Note the (Nitrate ion) moving beyond the root zone which explains why fertizers are requred by crops in every season.

    Inorganic Fertilizers

    Classification of inorganic fertilizers

    Inorganic fertilizers can be classified according to:
    (i)Main fertilizer element content
    (ii)Mode of application
    (iii)Time of application
    (iv)Effects of soil pH

    Nitrogenous fertilizer contain Nitrogen as the only primary macronutrient
    Examples include:
    o Calcium Ammonium Nitrate (CAN)
    o Ammonium Sulphate (AS)
    o Ammonium Sulphate Nitrate(ASN)
    o Urea

    Characteristics of nitrogenous fertilizers

    (i) Are highly soluble and hence easily leached

    (ii) Are highly volatile when exposed to high temperature

    (iii)Short residual effect.
    (iv)Have scotching effect on plants.
    (v) Highly corrosive.
    (vi) Hygroscopic.

    Observe keenly the scorched leaves of the tomato plant.

    Phosphate fertilizers

    Contain phosphorous as the only primary macronutrient.


    (i)Are sparingly soluble in water
    (ii)Have high residual effect.
    (iii)Are not liable to leaching.
    (iv)Have slight scorching effect and hence must be mixed with the soil after application.
    Farmers normally have varieties of phosphatic fertilizers to choose from as sources of phosphorous.Examples of phosphate fertilizers are SSP, DSP, basic slag, soda phosphate, and steamed bone meal.

    Observe white residues of DSP fertilizers.

    Potassic Fertilizers

    Contain potassium as the only primary macronutrient.
    -Have moderate scorching effect.
    -Have moderate solubility
    Examples of potassic fertilizers
    (i)Potassium chloride fertilizer
    (ii)Potassium sulphate

    Compound fertilizers

    Contain two or more of the primary macronutrients.
    Examples include Di-ammonium phosphate, mono-ammonium phosphate, Nitrophos and NPK 25:5:5+5S.
    Farmers have a variety of compound fertilizers available for crop production.

    Inorganic Fertilizers

    Foliar Feed Fertilizer
    Are fertilizers in solution form and sprayed onto the foliage leaves
    Examples include Greenzit and Bayfolan.


    Greenzit contains Nitrogen, Phosphorous, Potassium,Iron, Zinc, Manganese, Molybdenum, Copper, Nickel and Cobalt

    Foliar fertilizers Contains

    • Nitrogen
    • Potassium
    • Phosphorus

    It also contains; Vitamin B, growth hormones and all micronutrients.

    See the video below to appreciate foliar feed fertiliser application


    Inorganic Fertilizers

    Methods of Fertilizer Application

    (i) Broadcasting is a method of fertilizer application by scattering. It can be done by hand or mechanically by spreaders
    (ii) Placement method Involves fertilizer application within planting holes, furrows or drills.

    (iii) Side dressing is the placement of nitrogenous fertilizer at the side of the crop being top-dressed. Application can be in form of a band i.e. along the crop rows or in form of a ring around the crop.

    (iv)Foliar Spraying involves application of specially formulated fertilizer solution onto the foliage of the crop.

    See the video below to appreciate methods fertilizer application


    Inorganic Fertilizers

    Importance of soil sampling

    Soil sampling is recommended since testing all the soil from the whole piece of land is practically impossible.
    Soil sampling is done using traverse or zig-zag method.
    In traverse method, 4 corners of the field are marked and sampling locations arranged along diagonal line
    In zig zag method, a farmer moves and makes left to right sampling locations in random movements.
    Precautions to be avoided during soil sampling
    (i)Avoid any contamination with the soil
    (ii)Avoid mixing top soil and sub soil
    (iii)Avoid sampling soil from unusual areas such as anthills and dead furrows.

    Areas to be avoided when carrying out sampling

    (I) Swampy areas - tend to have more nutrient content than usual
    (ii)Terrace stand - tends to have higher nutrient content than usual
    (iii)Dead furrow tends to have less nutrient content than usual
    (iv)Manure heap - tends to have less nutrient content than usual

    Soil sampling

    Procedure to be followed when carrying out soil sampling

    1)Clear vegetation from sampling spots e.g. through slashing.
    2)Make vertical cut 5cm deep in pasture land and 15cm on crop land.
    3)Take a slice from the vertical cut.
    4)Repeat the above steps in each of the 20 sampling spots.
    5)Dry the sampled soil under shade.
    6)Break up the soil clods into fine particles.
    7)Thoroughly mix the soil samples.
    8)Should scoop out a sub-sample
    9)Put soil sample in a clean container.
    10)Label the container.

    See the video to appreciate how soil sampling is done.

    Zig-zag Method


    Methods of Soil Sampling

    The two methods of soil sampling are demostrated in the above pages

    Click Zig-zag method and Traverse method to open the demostration.

    Inorganic Fertilizers

    Soil Testing

    The process of soil testing involves the following steps:
    (v)Report writing

    Soil testing

    Involves analysis of the soil to;
    (i)Determine the cause of low yield.
    (ii)Estimate the supply of available nutrients.
    (iii)Indicate the soil pH.
    (iv)Indicate how much lime or fertilizer to be added into the soil.

    Note the increase in acidity as the arrow moves towards 1 and increase in alkalinity as the arrow moves towards 14 in pH scale.

    Importance of soil pH

    (i)Influences the availability of plant nutrients.
    (ii)Influences activity of micro-organisms in the soil.
    (iii)Influences the balance of various micro-organisms in the soil.
    (iv)Influence the occurrence and virulence of soil pests and pathogens.
    (v)Affects the growth and distribution of crops.

    See the video below to appreciate soil pH testing

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