Form 2 Agriculture Notes
Form 2 Agriculture Notes
Form 2 Notes
9.0.0 Soil Fertility H (Inorganic Fertilizers) (12 Lessons)
10.0.0 Crop Production II (Planting) (16 Lessons)
11.0.0 Crop Production HI (Nursery Practices) (16 Lessons)
12.0.0 Crop Production IV (Field Practices) (14 Lessons)
13.0.0 Crop Production V (Vegetables) (16 Lessons)
14.0.0 Livestock Health I (Introduction) (16 Lessons)
15.0.0 Livestock Health H (Parasites) (16 Lessons)
16.0.0 Livestock Production II (Nutrition) (12 Lessons)
Soil Fertility II
(Inorganic Fertilizers)
Introduction
• Plant nutrients occur in the soil in form of soluble substances.
• These substances are taken in by the plants in different quantities depending on their roles in the plant tissues.
Essential Elements
• These are nutrients needed by plants for various uses.
• They are divided into two broad categories namely:
– Macronutrients
– micronutrients.
Macro-nutrients
• These are also referred to as major nutrients.
• They are required by the plant in large quantities.
They include;
• carbon,
• hydrogen,
• oxygen,
• nitrogen,
• phophorus,
• potassium,
• sulphur,
• calcium
• magnesium.
– Nitrogen, phosphorus and potassium are referred to as fertilizer elements,
– Calcium, magnesium and sulphur, are referred to as liming elements.
Role of Macronutrients in Plants
Nitrogen (NO3,NH4++)
Sources:
• Artificial fertilizers
• Organic matter
• Atmospheric fixation by lightning
• Nitrogen fixing bacteria.
Role of Nitrogen in Plants
• Vegetative growth
• Chlorophyll formation
• Build up of protoplasm.
• Improves leaf quality in leafy crops such as tea and cabbages.
Deficiency Symptoms
• Yellowing of the leaves/chlorosis.
• Stunted growth.
• Premature ripening.
• Premature shedding of the leaves.
• Light seeds.
Effect of Excess Nitrogen
• Scorching of the leaves.
• Delayed maturity.
Loss of Nitrogen From the Soil:
• Soil erosion.
• Leaching.
• Volatilization.
• Crop removal.
• Used by microorganisms.
Phosphorus (H2 P04, HPO2-4 P2O5)
Sources:
• Organic manures
• Commercial fertilizers
• Phosphate rocks
Role of Phosphorus
• Encourages fast growth of the roots.
• Improves the quality of the plant.
• Hastens maturity of the crops.
• Influences cell division.
• Stimulates nodule formation in legumes.
Deficiency symptoms
• Growth of the plant is slow.
• Maturity is delayed.
• Leaves become grey, purple in colour.
• Yield of grains, fruits and seed is lowered.
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Loss of Phosphorus From the Soil
• Soil erosion.
• Leaching
• Crop removal
• Fixation by iron and aluminium oxide.
Potasium (K+, K2O)
Sources;
• Crop residue and organic manures.
• Commercial fertilizers
• Potassium bearing minerals e.g. feldspar and mica.
Role of Potassium in Plants
• Increases plant vigour and disease resistance.
• Increases the size of grains and seeds.
• Reduces the ill-effects due to excess nitrogen.
• Prevents too rapid maturation due to phosphorus.
Deficiency Symptoms
• Plants have short joints and poor growth.
• Plants lodge before maturing.
• Leaves develop a burnt appearance on the margin.
• Leaves at the lower end of the plant become mottled, spotted or streaked.
• In maize, grains and grasses firing starts at the tip of the leaf and proceeds from the edge usually leaving the midrib green.
Loss of Potassium From the Soil
• Crop removal.
• Leaching.
• Soil erosion.
• Fixation in the soil.
Calcium (Ca2+)
Source:
• Crop residues and organic manures.
• Commercial fertilizers.
• weathering of soil minerals.
• Agricultural limes for example dolomite, limestone.
Role of Calcium in Plants
• Improves the vigour and stiffness of straw.
• Neutralizes the poisonous secretions of the plants.
• Helps in grain and seed formation.
• Improves the soil structure.
• Promotes bacterial activity in the soil.
• Corrects the soil acidity.
Deficiency symptoms
• Young leaves remain closed.
• There are light green bands along the margins of the leaves.
• Leaves in the terminal bud become hooked in appearance there is a die-¬back at the tip and along the margins.
Loss of Calcium
• Crop removal
• Leaching
• Soil erosion
Magnesium (Mg2+)
Sources:
• Crop residues and organic manures
• Commercial fertilizers
• Weathering of soil minerals.
• Agricultural limes.
Role of Magnesium in Plants
• Forms part of chlorophyll.
• Promotes the growth of the soil bacteria and enhances the nitrogen fixing power of the legumes.
• Activates the production and transport of carbohydrates and proteins in the growing plant.
Deficiency symptoms
• Loss in green colour which starts from the bottom leaves and gradually moves upwards.
• The veins remain green.
• Leaves curve upwards along the margins.
• Stalks become weak and the plant develops long branched roots.
• The leaves become streaked.
Sulphur (S04 2- ,SO2)
Sources:
• Commercial fertilizers.
• Soil mineral containing sulphides
• Atmospheric sulphur from industries.
• Rain water
Role of Sulphur in Plants
• Formation and activation of coenzyme-A.
• Sulphur is a constituent of amino acids.
• Influence plant physiological processes.
Deficiency Symptoms
• Small plants/stunted growth.
• Poor nodulation in legumes.
• Light green to yellowish leaves/ chlorosis.
• Delayed maturity.
Micro-nutrients
• Also referred to as trace or minor nutrients.
• They are required in small quantities/traces.
• They are essential for proper growth and development of plants.
They include;
• Iron,
• Manganese,
• Copper,
• Boron,
• Molybdenum
• Chlorine.
Role of Micronutrients and Their Deficiency Symptoms
• Copper
– Role in oxidation-reduction reactions.
– Respiration and utilization of iron
– Deficiency symptoms-yellowing of young leaves.
• Iron
– Synthesis of proteins.
– Takes part in oxidation-¬reduction reactions.
– Deficiency symptoms – leaf chlorosis
• Molybdenum
– Nitrogen transformation in plants.
– Metabolization of nitrates to amino acids and proteins
– Deficiency symptoms -leaf curl and scathing.
• Manganese – Same as molybdenum.
• Zinc
– Formation of growth hormone.
– Reproduction process
– Deficiency symptoms – white bud formation.
• Boron
– Absorption of water.
– Translocation of sugar
Inorganic Fertilizers
• These are chemically produced substances added to the soil to improve fertility. Classification According to:
• Nutrients contained
– Straight – contain only one macronutrient.
– Compound fertilizers – contain more than one macronutrient
• Time of application
– Some applied when planting.
– Top dressing after crop emergence
• Effects on the soil pH.
– Acidic fertilizers.
– Neutral fertilizers.
– Basic fertilizers.
Properties and Identification of Fertilizers
Nitrogenous Fertilizers
Characteristics
• Highly soluble in water.
• Highly mobile in the soil hence it is applied as a top dress.
• Easily leached because of the high solubility hence does not have residual effect on the soil.
• Has scorching effect on young crops during wet seasons.
• Easy to volatilize during hot season.
• They have a tendency to cake under moist conditions.
• They are hygroscopic hence should be stored in dry conditions.
Examples:
• Sulphate of Ammonia (NH4) 2 SO4
• Physical appearance:
– white crystals,
– Has acidic effect,
– Contains 20% N.
• Ammonium Sulphate Nitrate [(NH4)2 SO4+ NH4 NO3]
– Colour: granules which appear yellow orange,
– less acidic,
– contains 26% N.
• Calcium Ammonium Nitrate (CAN)
– Colour: greyish granules,
– neutral in nature,
– contains 21 % N.
• Urea
– Colour: small whitish granules
– Easily leached or volatilized,
– contains 45- 46%N.
Phosphate Fertilizers
• Has low solubility and immobile.
• Non-scorching.
• Has a high residual effect hence benefit the next season’s crop.
• Easy to store because they are not hygroscopic.
Examples;
• Single super-phosphate
– Appearance: whitish, creamy white granules,
– contains 20-21 % P2O5
• Double super-phosphate
– Appearance: dark greyish granules,
– Contains 40-42% P2O5
• Triple super-phosphate
– Appearance: small greyish granules,
– Contain 44-48% P2O5
Potassic Fertilizers
Characteristics:
• Has moderate scorching effect.
• Moderately soluble in water.
• Most Kenyan soils have sufficient potassium.
Examples;
• Muriate of Potash (KCl)
– Contain 60 – 62% K2O
– Slightly hygroscopic.
– Appearance amorphous white.
• Sulphate of Potash (50% K2O)
Compound or Mixed Fertilizers
• These are fertilizers which supply 2 or more of the macronutrients.
Examples;
• Mono ammonium phosphate.
• Di-ammonium phosphate
• 20:20:20, 23:23:23
Advantages of application of compound fertilizers
• Saves time and money.
• Mixture gives improved storage properties and better handling.
Disadvantages of compound fertilizers application
• Expensive.
• Wasteful.
• Mixing may not be thorough.
• Incompatibility of the individual fertilizers.
Methods of fertilizer application
• Broadcasting – random scattering of the fertilizers on the ground.
• Placement method – application of fertilizers in the planting holes.
• Side dressing – fertilizer is placed at the side of the plant within the root zone, in bands or spot-rings.
• Foliar spraying – specially formulated fertilizer solution applied on the foliage in spray form.
• Drip method – applied through irrigation water.
Determination of Fertilizer Rates
Contents of fertilizers are expressed as fertilizer grade or fertilizer analysis.
• Fertilizer grade indicate the guaranteed minimum of the active ingredients (N, P2O5, K 2O) in the mixture.
• It is expressed as a percentage on a weight to weight basis or percentage by weigh
Example 10:20:0 means for every 10kg of the mixture there are 10kg of nitrogen, 20kg of P2O 5 and 0kg of K2O.
Example
A farmer was asked to apply fertilizers as follows:
• 60 kg/ha nitrogen (top dressing)
• 60 kg/ha P2O5 (in planting hole).
• 60 kg/ha K2O.
How much sulphate of ammonia (20%) would be required per hectare?
How much double super-phosphate (40%) P2O5would be required per hectare?
How much muriate of potash (50% K2O) would be required per hectare?
Answer/Solution
• Sulphate of ammonia (SA) which gives 60kg/ha N = 60
20x 100 =300kg SA
• Double super phosphate (40% P2O5)which gives 60kg/ha P2O5 60
= 40x 100 =150kg DSP
• Muriate of potash (60% K2O) which gives 60kg/hK2O
= 60 x 100=100kg muriate of potash
60
Example
A farmer was asked to apply fertilizers as follows:
• 200kg/ha of DSP (40% P2O5
• 150kg/ha of muriate of potash (60% K2O)
• 150kg/ha of sulphate of ammonia (20% N)
How much P2O5 did the farmer apply per acre?
How much K2O did the farmer apply per hectare?
How much N did the farmer apply per hectare?
Solution/Answer
• P2O5 applied per hectare from 200kg of DSP 40
= 100x 200= 80kg/ha P2O 5
• K2O 5 applied per hectare from 150kg of muriate of potash 60
= 100×150=90kg/ha K2O
• N applied per hectare from 150kg/ha sulphate of ammonia 20
= 100 x 150= 30kg/ha N
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