Agriculture Notes

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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
Ø Know the course of action to be taken in the event of a disease and maintenance of good health.

ØSoil 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

Ø Know the course of action to be taken in the event of a disease and maintenance of good health.
Ø Know the prevalent diseases.
Ø Calculate the cost of treatment.

Marketing Records show commodities sold, quantities and value of all the sales.

Labour Records - show labour utilization and lab Know the prevalent diseases.

Ø 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.

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:

Ø Name of the farmer,
Ø Location,
Ø District
Ø 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
Traverse method

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

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.

Potassic Fertilizers

Characteristics:

Has moderate scorching effect.
Moderately soluble in water.
Most Kenyan soils have sufficient potassium.

Examples;

· Muriate of Potash (KCl)

Ø Contain 60 - 62% K2O
Ø Slightly hygroscopic.
Ø 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.

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

Ø Appearance: whitish, creamy white granules,
Ø contains 20-21 % P2O5

· Double super-phosphate

Ø Appearance: dark greyish granules,
Ø Contains 40-42% P2O5

· Triple super-phosphate

Ø Appearance: small greyish granules,
Ø Contain 44-48% P2O5

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:

Ø white crystals,
Ø Has acidic effect,
Ø Contains 20% N.

· Ammonium Sulphate Nitrate [(NH4)2 SO4+ NH4 NO3]

Ø Colour: granules which appear yellow orange,
Ø less acidic,
Ø contains 26% N.

· Calcium Ammonium Nitrate (CAN)

Ø Colour: greyish granules,
Ø neutral in nature,
Ø contains 21 % N.

· Urea

Ø Colour: small whitish granules
Ø Easily leached or volatilized,
Ø contains 45- 46%N.

Inorganic Fertilizers

These are chemically produced substances added to the soil to improve fertility.

Classification According to:

· Nutrients contained

Ø Straight - contain only one macronutrient.
Ø Compound fertilizers - contain more than one macronutrient

· Time of application

Ø Some applied when planting.
Ø Top dressing after crop emergence

· Effects on the soil pH.

Ø Acidic fertilizers.
Ø Neutral fertilizers.
Ø Basic fertilizers.

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

Ø Role in oxidation-reduction reactions.
Ø Respiration and utilization of iron
Ø Deficiency symptoms-yellowing of young leaves.

· Iron

Ø Synthesis of proteins.
Ø Takes part in oxidation-­reduction reactions.
Ø Deficiency symptoms - leaf chlorosis

· Molybdenum

Ø Nitrogen transformation in plants.
Ø Metabolization of nitrates to amino acids and proteins
Ø Deficiency symptoms -leaf curl and scathing.

Manganese - Same as molybdenum.

Zinc

Ø Formation of growth hormone.
Ø Reproduction process
Ø Deficiency symptoms - white bud formation.

· Boron –

Ø Absorption of water.
Ø Translocation of sugar

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.

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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.

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