fertlizer elements
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.
![combined.jpg](https://peda.net/kenya/ass/subjects2/agriculture/form-two/topic-one/crop-production-2/fertlizer-elements/combined-jpg:file/photo/f6d25de37466c971e62931f3cac229ff40185e36/combined.jpg)
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.
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.
![margins.jpg](https://peda.net/kenya/ass/subjects2/agriculture/form-two/topic-one/crop-production-2/fertlizer-elements/margins-jpg:file/photo/bd1e1bd6ac7a778aa521f00010eee20060804515/margins.jpg)
- Leaves at the lower end of the plant become mottled, spotted or streaked.
![burnt.jpg](https://peda.net/kenya/ass/subjects2/agriculture/form-two/topic-one/crop-production-2/fertlizer-elements/burnt-jpg:file/photo/96dd5467c24bb70a99ad62e508bc132b72022a5c/burnt.jpg)
- In maize, grains and grasses firing start
- s 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-
- 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
- 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.
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 % P2O
- 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;
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
- K2O5 applied per hectare from 150kg of muriate of potash
60
= 100x150=90kg/ha K2O
- N applied per hectare from 150kg/ha sulphate of ammonia
20
= 100 x 150= 30kg/ha N
Soil Sampling
- Refers to obtaining of small quantity of soil that is representative in all aspects of the entire farm.
Soil Sampling Procedures
- Clear the vegetation over the site.
- Dig out soil at depths of 15-25cm.
- Place the dug out soil in a clean container.
- Mix thoroughly the soil in the container.
- Take a sample and send it to National Agricultural Laboratory for analysis.
- The container carrying the sample should be properly labeled as follows:
- Name of the farmer,
- Location,
- District
- Address of the farmer.
Sites to Avoid
- Dead furrows, ditches.
- Swamps
- Near manure heaps.
- Recently fertilized fields
- Ant hills.
- Under big trees.
- Near fence lines or foot paths.
Do not put them in containers which are contaminated with fertilizers or other chemical containers.
Methods Of Soil Sampling:
- Zigzag method
![zigzag.jpg](https://peda.net/kenya/ass/subjects2/agriculture/form-two/topic-one/crop-production-2/fertlizer-elements/zigzag-jpg:file/photo/32304e08bcb1ce5dbe40db4d2c35f509f28daa5b/zigzag.jpg)
- Traverse method
Soil Testing
- Soil testing is the analyzing of the soil sample to determine certain qualities of the soil.
Importance of Soil testing:
- To determine the value of the soil hence determine the crop to grow.
- To determine the nutrient content hence find out the type of fertilizer to apply.
- To determine whether it is necessary to modify the soil pH for a crop.
How Soil pH affects Crop Production
- Influences the physical and chemical properties of the soil.
- Affects the availability of nutrients.
- Influences the incidences of soil borne diseases.
- Determine the type of crop to be grown at a given area.
Methods of pH Testing
- Universal indicator solution
- pH meter
- Know the course of action to be taken in the event of a disease and maintenance of good health.
- Know the prevalent diseases.
- Calculate the cost of treatment.
- Marketing Records show commodities sold, quantities and value of all the sales.
Labour Records - show labour utilization and labour costs.