HomeAGRICULTURE NOTESSOIL FERTILITY(II) :INORGANIC FERTILISERS.

SOIL FERTILITY(II) :INORGANIC FERTILISERS.

SOIL FERTILITY(II) :INORGANIC FERTILISERS.

SOIL FERTILITY(II) :INORGANIC FERTILISERS ,Soil fertility.-ability of soil to supply nutrients to plants in correct amount/proportion and form.

Plants nutrients classification.

  1. Macro-nutrients.
  2. Micro-nutrients.

Macro nutrients/major nutrients

These are required by plants in large quantities.

Include:

  • Carbon
  • Hydrogen
  • Nitrogen
  • Phosphorus
  • Potassium
  • Sulphur
  • Calcium
  • Magnesium

The macro nutrients are further categorised into two broad categories. 

  1. Fertilizer elements.
  • Nitrogen
  • Calcium
  • Magnessium

The above are referred to as the primary macro nutrients and are required by plants in large proportions.

Liming elements.

  • Sulphur
  • Calcium
  • Magnesium

Role of macro-nutrients and their deficiency.

Nitrogen.

Occurs as N2 gas in the atmosphere .plants absorb nitrogen in ionic form in form of:

  • Nitrate ions NO3
  • Ammonium ions. NH4+

Nitrogen gets into the soil through nitrogen fixation by micro-organism and lightning.

Nitrogen is soluble in water and can be leached during heavy rains.

ROLE OF NITROGEN IN PLANTS

  • Plays an important role in protein formation .it is a constituent element of proteins and protoplasm.
  • Forms parts of chlorophyll molecule and makes the plant succulent with a deep green colour.
  • Encourages vegetative growth especially in horticultural crops where leaves are harvested.
  • Regulate availability of phosphorus and potassium in plants.
  • In cereals, nitrogen increases size of grains and their protein content.

Symptoms of nitrogen deficiency 

  • Chlorosis-plants leaves lose chlorophyll and becomes yellow.
  • Sometimes leaves loses chlorophyll and falls off prematurely.
  • Stunted growth with extremely short roots.
  • Production of anthocyanin pigment in tomatoes (purplish colour.)

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SOIL FERTILITY(II) :INORGANIC FERTILISERS.

Effects of excess nitrogen in the soil.

  • Delayed maturity due to excessive vegetative growth at the expense of reproductive growth.
  • Causes excessive succulence making plants liable to pest damage.
  • Causes lodging in cereals.
  • Causes blossom end rot in tomatoes.

 PHOSPHORUS.

Exist either in inorganic or organic form. The action of soil micro-organisms convert organic phosphorus into phosphates.

Form absorbed by plants is: HPO2-4.

Phosphates are relatively insoluble in soil.

Role of phosphorus in plants.

  • Root development. Stimulates nodule formation in leguminous crops.eg beans, peas etc.
  • Essential for flowering, fruits and seed development and hastens ripening of fruits.
  • Strengthens the plant stems thus preventing lodging.  Part of nucleoproteins required during cell division.

Symptoms of phosphorus deficiency.

  • Increases production of anthocyanin giving plants a purplish colour.
  • Stunted growth of green parts and poor development of metabolising organs.

NB: excess phosphorus leads to unavailability of iron.

POTASSIUM.

It is a constituent element of clay particels.it is easily leached in sandy soils.

Role of potassium in plants.

  • Plays an important role in carbohydrates formation and translocation.
  • Necessary for neutralization of organic acids in plants.
  • Assists in the uptake of nitrates and has a balancing effects on P and N uptake.  Component of chlorophyll molecule.

Symptoms of potassium deficiency.

  • Leaf curling.
  • Leaf surfaces lose chlorophyll and becomes yellowish i.e. they become chlorotic.
  • Stunted growth.
  • Edges of leaves are scorched while the central part remain green.

MAGNESIUM.

It is readily leached in soils that receive high rainfall.

Role of magnesium in plants.

  • Required in the synthesis of oil.
  • Promotes growth of soil bacteria and ability of leguminous crops to fix nitrogen.

Symptoms of magnesium deficiency.

  • Interveinal Chlorosis of leaves.
  • Anthocyanin pigment develops after Chlorosis, later the leaves turn brown and die.
  • In horticultural crops, leaves develops purple-orange and red patches.

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SOIL FERTILITY(II) :INORGANIC FERTILISERS.

SULPHUR.

It exist in soil in form of organic sulphates or inorganic form as pyrites or gypsum.it is absorbed in form of sulphate ions. (SO2-4) following decomposition of organic matter and mineralisation of pyrites or gypsum.

Role of sulphur in plants.

  • Necessary for formation of proteins and plants hormones.
  • Necessary in formation and activation of certain co-enzymes such as co-enzyme A.
  • Influences plant physiological process e.g. protein formation, CHO metabolism, nitrogen fixation and chlorophyll formation.
  • Stunted growth.
  • Leaf Chlorosis followed by production of anthocyanin.
  • Thin stems and reduced nodulation in legumes.

Soil calcium is derived from rocks through the process of weathering. It is absorbed as calcium ions.  (CA2+)

CALCIUM.

Role of calcium in plants.

  • Promotes formation of aggregates thus improves soil aeration, water infiltration and retention.
  • Calcium compounds are added to acidic soils (pH 5 to raise it to pH 6-7) which increases bacterial activities e.g. nitrogen fixation.
  • It raises the soil pH which increases CEC and makes more nutrients i.e. Pand K available.
  • Calcium strengthens plant cell walls with calcium acetate. Used during cell division.  Necessary in protein synthesis.

Symptoms of calcium deficiency.

  • Stunted growth.
  • Dying back of plant tips.
  • Blossom end rot in tomatoes.

MICRO-NUTRIENTS AND THEIR DEFICIENCY.

Micro –nutrients are needed by plants in relatively small quantities .they acts as catalysts and co-enzymes in metabolic reactions of plants.

Examples.

  1. Copper, iron and molybdenum play an important part in enzyme systems which bring about oxidation and reduction (Redox) reactions in plants.
  2. Copper is involved in the respiration and utilisation of iron.
  3. Iron is necessary for synthesis of proteins in the chloroplasts.
  4. Molybdenum and manganese are essential for ceartin nitrogen transformation reactions in plants as well as in micro-organisms. Molybdenum is essential for the process of nitrogen fixation by symbiotic and non-symbiotic bacteria. It must be present in plants if nitrates are to be metabolised into amino acids and proteins.
  5. Zinc takes part in the formation of some growth hormones and in the reproduction process of some plants.
  6. Boron is involved in the absorption of water and translocation of sugar in plants.

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SOIL FERTILITY(II) :INORGANIC FERTILISERS.

 IONIC FORMS AND DEFICIENCY SYMPTOMS OF PLANT NUTRIENTS.

Nutrient. Symbol. Form absorbed. Deficiency symptoms.
Macro nutrients.
Nitrogen. N. NO-3, NH+4 Chlorosis, stunted growth, premature leaf fall, production of anthocyanin.
Phosphorous. p. H2PO-4, HPO2-4 Stunted growth, slender stalks, delayed maturity, production of anthocyanin.
Potassium. k. K+ Leaf curling, leaf surface chlorosis, premature leaf fall, stunted growth, edges of leaves scorched.
Magnesium. Mg. Mg2+ Inter venial chlorosis, production of anthocyanin.
Sulphur. S. SO2-4, Stunted growth, leaf chlorosis, and thin stems and reduced nodulation in legumes.
Calcium. Ca. Ca2+ Die back of tips, stunted growth.
Carbon. C. CO2 Poor formation of woody parts.
Hydrogen. H. Wilting of entire plant.
Oxygen. O Wilting of entire plant.
Micro-nutrients.
Copper. Cu. Cu2+ Leaves and stems grow longer than normal, young leaves almost without chlorophyll.
Iron. Fe. Fe2+ Leaf chlorosis.
Molybdenum. Mo. Leaf curling and leaf scorch.
Zinc. Zn. Zn2+ White bud formation, young leaves almost without chlorophyll.

Inorganic fertilizers.

These are artificially processed compounds added into soil to improve its fertility. They contain one or more macro nutrients.

CLASSIFICATION OF INORGANIC FERTILIZERS.

They are classified on the following basis.

  • Nutrients contained.
  • Mode of application.
  • Time of application.  Effects on soil pH.

Classification based on nutrients contained.

Based on this fertilizers can be classified into two

  • Straight fertilizers.
  • Compound fertilizers.

Straight fertilizers.

These are fertilizers that contain only one primary macro nutrients. They are named according to the nutrient they contain. These are:

  • Nitrogenous fertilizers.
  • Phosphatic fertilizers.  Potassic fertilizers.

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SOIL FERTILITY(II) :INORGANIC FERTILISERS.

Nitrogenous fertilisers.

They contain nitrogen as the only primary macro nutrient.

Examples.

  • Calcium ammonium nitrate. (CAN)
  • Sulphate of ammonia. (SA)  Ammonium sulphate nitrate. (ASN) 

Phosphatic fertilizers.

They contain phosphorous as the only primary macro nutrient.

Examples.

  • Single super phosphate. (SSP)
  • Double super phosphate. (DSP)
  • Triple super phosphate. (TSP)

Potassic fertilizers.                                    

They contains potassium as the only primary macro nutrients.

Examples.

  • Muriate of potash/potassium chloride. (KCL)
  • Potassium sulphate/sulphate of potash. (K2SO4)

PROPERTIES AND IDENTIFICATION OF FERTILISERS.

NITROGENOUS FERTILIZERS.

Characteristics of nitrogenous fertilizers.

  • They are highly soluble in soil water.
  • They are easily leached to lower horizons. Thus they should be applied to an already established crop.
  • They have a short residual effect hence should be applied frequently.
  • They have a scorching/burning effect on plants thus should not come into contact with the crop except for foliar fertilisers.
  • They are highly volatile .under hot conditions, they change into gaseous form and escape into the atmosphere.
  • Most are highly corrosive. They corrode the epithelial cells of palms and should not be handled with bare hands. They also corrode metal surfaces e.g. iron and tin.
  • They are hygroscopic .that is they absorb moisture from the atmosphere and cake. The granules sticks together.

 PROPERTIES OF INDIVIDUAL NITROGENOUS FERTILIZERS. 

Ammonium sulphate. (Sulphate of ammonia)

(NH4)2SO4

  • It contains 20-21%N inform of ammonium thus is slow acting.  It is acidic and highly volatile. Ammonium sulphate nitrate (ASN)

NH4NO3 + (NH4)2SO4

It is a mixture of ammonium sulphate and ammonium nitrate.

  • It has a nitrogen content of 26%.
  • It is less acidic.
  • It is highly corrosive. And it is both quick and slow acting because of nitrates and ammonium respectively.

Calcium ammonium nitrates.

NH4NO3 + CACO3

  • It is a mixture of ammonium nitrate and calcium carbonate. The nitrogen content is 21%.it is a neutral fertilizer because the acidity caused by ammonium ions is counteracted by the liming effects of calcium carbonate.
  • CACO3 improves the soil structure in soils with poor drainage.
  • It is highly hygroscopic.  It causes no corrosion.

Urea   

  • It contains 45-46%N.
  • It induces negligible acidity.
  • It is lost in the process of volatilisation and leaching.
  • It has a scorching effects due to the ammonium content.
  • It is very soluble in water and is easily leached.
  • It is applied in crops with high absorption capacity e.g. sugarcane.

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PHOSPHATIC FERTILIZERS. 

Characteristics.

  • They are sparingly soluble in water but are readily converted into di-calcium ions which combine with aluminium ions to form compounds not available to plants. That is, they are fixed.
  • They have a residual effect and their reconversion into mono-calcium forms is very gradual.
  • They are not liable to leaching thus they are applied early.
  • They have a slight scorching effect and have to be mixed well with soil to minimise scorching effect.

Reasons for application of Phosphatic fertilises during planting.

  • They are not liable to leaching.
  • They have a slight scorching effect thus has to be mixed well with soil to reduce tis effect.
  • They have a residual effect and their reconversion to mono-calcium forms is slow thus benefits subsequent crops.
  • They are easily fixed into unavailable forms thus should be placed in the rooting zone of plants so as it is utilised before it become fixed.

PROPERTIES OF INDIVIDUAL PHOSPHATIC FERTILISERS.

Single superphosphate. 

  • Contains 20-21% P2O5
  • It induces negligible acidity to the soil.
  • It supplies phosphorous. Calcium and sulphur.
  • It should not be stored with ammonium containing fertilisers due to the presence of calcium.

Double and triple superphosphates.

Induces negligible acidity in the soil.

  • Contains 43-52% P2O5

POTASSIC FERTILISERS. 

Characteristics. 

  • Have moderate scorching effect.
  • Moderately soluble in water than P but less soluble than N.
  1. Soil in East Africa have abundant K.

PROPERTIES OF INDIVIDUAL POTASSIC FERTILIZERS. 

Potassium chloride. (KCL)

  • Contains 50% potassium oxide K2O  Induces negligible acidity.  It is hygroscopic.

Potassium sulphate. (K2SO4)

  • Contains 50% K2O and provide mainly potassium, sulphur and a few trace elements.
  • Induces negligible acidity in the soil.

 COMPOUND/MIXED FERTILISERS. 

They are made by mixing 2 or more straight fertilisers. The nutrients they contain is expressed in 2 ways.

  • Fertiliser grade.  Fertiliser ratio.

Fertiliser grade.

  • It indicates a guarantee of minimum content as a percentage of N: P2O5: K2 E.g. 10-20-0.

Fertiliser ratio. 

Indicate the relative percentage expressed as a ratio of NPK present .e.g. 10-20-0 as a ratio becomes 1:2:0

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SOIL FERTILITY(II) :INORGANIC FERTILISERS.

PROPERTIES OF INDIVIDUAL COMPOUND FERTILISERS.

Diammonium phosphate.  DAP (NH4)2PO4  

It has a fertiliser grade of 18-46-0

It is moderately acidic because of the ammonium content.

Monoammonium phosphate. MAP

11-48-0

Others include:

  • NPK 23:23:23 NPK 17:17:0 NPK 20:10:10

FERTILISER APPLICATION.

Methods of fertiliser application.

Includes.

  • Placement method.
  • Side dressing.
  • Foliar spraying.

Broadcasting

Involves random scattering of fertilizer on the ground. Applicable with nitrogenous fertilizers and potassic fertiliser. Fertilizer should be shallowly dug into the soil to prevent loss through volatilisation.

Placement method.

Application of fertiliser in planting holes/drills. Used in application of Phosphatic fertilisers and should be mixed thoroughly with soil.

Side dressing. 

Placement of nitrogenous fertiliser at the side of the crop being top-dressed.

Includes:

Band application.

Placement of fertilisers along a band in between the rows of growing crops.

Ring application.

Placement of fertiliser on individual crop.

Foliar spraying. 

Application of specially formulated fertiliser solution onto the foliage and it is absorbed by leaves.

When to do foliar spraying. 

  • During prolonged dry spell.
  • When topdressing closely spaced crops such as wheat.  For micro nutrients.

Drip application/fertigation.  

Application of fertiliser dissolved in irrigation water and it applied to individual crop during irrigation.

DETERMINATION OF FERTILISER RATES.

 Calculations involving fertiliser application.

  1. Fertiliser grade/analysis.

Fertiliser grade indicates amount of each nutrient contained in a fertiliser.

% of nutrients = Nutrient content/Total weight of fertiliser x100

It is calculated in terms of NPK and is indicated on the fertiliser bags.

Example. One bag of 100kg of fertiliser of 10-10-10 grade contains 10kg N 10kg P2O5 and 10kg K2O.

Thus 30kg are the active element while the reaming 70kgs is filler/carrier material.

Fertiliser grade guides on amount of fertiliser to apply.

  1. Fertiliser Ratio.

It is the relative proportion of NPK in a fertiliser.eg a 10-10-10 grade has a ratio of 1:1:1

  1. Amount of fertiliser or nutrients required per unit area. (Per Ha)

This depends on nutrients needed and the fertiliser grade available.

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SOIL FERTILITY(II) :INORGANIC FERTILISERS.

 Example 1

Suppose a soil is deficient in all the 3 primary macro nutrients and in a field test it is found out that the following should be applied.

60kgN, 30kg P2O5 and 40kg K2O  per ha.Calculate the amount of S.A ,SSP and KCL required pee Ha if the fertiliser available are sulphate of ammonia (SA) 20%N,SSP 20% P2O5 and Muriate potash 50%  K2O.

Solution.

  1. Sulphate of ammonia.

100kg SA ——————–20kgN

X                6okgN

=60kgNX100KG SA/20KG N

=300kgSA

  1. Total amount of SSP.

100kgSSP—————–20KG P2O5

X                   30Kg

=100kgSSP X 30kg P2O5/20Kg P2O5 =150kg SSP

  1. Total amount of K2O

100Kg K2O —————————-50Kg K2O

X                   40Kg K2O

=80Kg KCL

Example two

A farmer was advised to apply 150kg CAN/Ha while topdressing his maize crop. CAN contains 21%N.

Calculate the amount of nitrogen applied per/Ha Solution.

21kgN ————100KgCAN

X          150KgCAN

21KgNX150KgCAN/100KgCAN =31.5KgN/Ha.

 THE NITROGEN CYCLE. 

It is a series of changes which nitrogen undergoes between the atmosphere, water, soil and living organisms.

WAYS IN WHICH NITROGEN IS REMOVED FROM THE ATMOSPHERE.

  1. Nitrogen fixation by lighting

N2 (g) + O2  2NO

2NO +H2O  HNO2 + HNO3

  1. Nitrogen fixation by Nitrogen fixing bacteria.

Nitrogen fixation by nitrogen can be in two forms

Symbiotic nitrogen fixation by bacteria of Rhizobium.

Non –symbiotic nitrogen fixation by free living bacteria e.g. Clostridium and Azotobacter.

  1. Nitrification

Process by which ammonium compounds are converted into nitrites and then nitrates.

  1. Harber-Bosch process.

It is the chemical preparation of ammonia.

N2+H2       2NH2.

WAYS IN WHICH NITROGEN IS RETURNED FROM THE ATMOSPHERE.

  1. Denitrification

Conversion of nitrates ions into ammonia gas and ammonium ions into ammonia gas.it is common in waterlogged soils.

  1. Combustion

Burning of vegetation causes conversion of nitrogenous compounds into nitrogen (IV) oxide and ammonia.

  1. Volatilisation.

Ammonium compounds in soil sublime to form ammonia gas. 

SOIL SAMPLING. 

Process of taking a small quantity of soil from the field to act as a representative sample of the soil in that field.

Soil sampling methods.

  • Traverse
  • Zigzag

 Areas to avoid taking samples from.

  • Dead furrows.
  • Terrace stand.
  • Swampy areas.
  • Between slopes and bottom lands.
  • Near trees and boundaries.
  • Old fence lines.
  • Old manure heaps.

Such areas are not a representative of the field and they give misleading results.

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Soil sampling procedure.

  1. Vegetation from the sampling spot is cleared and a vertical cut is made to a depth of 15-25cm for cropland and 5cm for pasture land.
  2. A slice is taken from the vertical cut using a soil auger or a spade.
  3. Soil is put in a clean container.
  4. The steps above are repeated in different spots 15-20 spots. Soil from all the spots is thoroughly mixed dried and crushed.
  5. A sub-sample (composite) from the mixture is taken for analysis.

Information on the sub-sample.

  • Name and address of the farmer.
  • Field number.
  • Date of sampling.

Soil testing.

Process of analysis the soil sample to determine the ability to supply the essential elements.

Importance of soil testing.

  • Information obtained may indicate how much lime and fertiliser one should use.
  • Helps to estimate the supply of available nutrients.  Helps in diagnosing the cause of low crop yields.

SOIL PH.

Measure of acidity or alkalinity of soil solution. Soil acidity is caused by H+ while soil alkalinity is caused by OH. Mathematically soil pH is= negative log to base 10 of H+  Testing soil pH.

  • Use of pH metre which is expensive.  Use of colour indicator dyes.

The pH scale.

Used to estimate the degree of acidity or alkalinity of a solution.

  • Most nutrients are available at around neutral. E.g. phosphates 6.5-7.5.
  • Low soil pH lowers availability of P as phosphates becomes immobile/fixed.
  • Micro-nutrients are also unavailable at low pH.
  • Too high pH. Renders some nutrients unavailable e.g. pH. 8.5> manganese, boron, iron and zinc are less available.

Importance of soil pH to crops.

  • Low pH inhibits activities of soil micro-organisms especially NFB. Low soil pH favours fungi and discourages bacteria  Soil pH determines the presence or absence of nutrients.
  • Plant damage by various soil pests e.g. nematodes is more severe in acidic soils. Due to lowering of plants resistance.
  • Different crop species performs within a range of soil pH. E.g. tea at pH 4.5.

   ALL AGRICULTURENOTES FORM 1-4 WITH TOPICAL QUESTIONS & ANSWERS          PRIMARY NOTES, SCHEMES OF WORK AND EXAMINATIONS

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