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Soil
 

Soil

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    Soil Soil Presentation Transcript

    • Soil is composed of:Soil is composed of:  rock particles  humus  mineral salts  water  air  organisms
    • Rock particlesRock particles  vary in size Gravel Sand Silt Clay
    • Three types of Soil:Three types of Soil: Clay Sandy Loam BESTBEST TYPETYPE
    • ThreeThree types of soil:-types of soil:- 2 Sand : 1 Clay2 Sand : 1 Clay
    • Clay Soil:Clay Soil:  heavy soil  difficult to dig as clay sticks
    • Clay Soil:Clay Soil:  when dry it forms hard clods  little air present Clay Sandy Loam
    • Clay Soil:Clay Soil:  retains water  soil becomes waterlogged
    • A waterlogged soil has few air spaces as these become filled with water
    • 1. amount of air Particle size affects theParticle size affects the following properties of soil:-following properties of soil:-
    • 2. the rate and amount of drainage Particle size affects theParticle size affects the following properties of soil:-following properties of soil:-
    • 3. the rise of water in the soil (capillarity) Capillary waterCapillary water
    • The smaller the particle size, the higher water rises.
    • Question: [APRIL, 2010]Question: [APRIL, 2010] Paper 2BPaper 2B List TWO properties of soil that are affected by soil texture. (4)  The distance between soil particles  The amount of air between soil crumbs/drainage  The rise of water in the soil (capillarity) Any TWO
    • Clay Soil is made lighter byClay Soil is made lighter by adding:-adding:- i) humus How do these work? ii) lime
    • AddingAdding limelime
    • Clumping of soil particlesClumping of soil particles introduces air in soilintroduces air in soil A clay soil before treatment. lime humus A clay soil after treatment.
    • Good crumb structureGood crumb structure [texture] of soil[texture] of soil
    • What is ‘humus’?What is ‘humus’? black or dark brown material that remains after decomposition
    • Dark soil: rich in humusDark soil: rich in humus
    • 0-45cm 45-90cm Bedrock Upper topsoil layer is dark. Why? Lower soil layer is rich in salts. Why? Lower soil layer is rich in salts. Why?
    • Question: [APRIL, 2010] Paper 2BQuestion: [APRIL, 2010] Paper 2B Explain how humus: i) Increases the soil’s water content. (2) Absorbing large amounts of water or reducing evaporation from the soil.
    • Question: [APRIL, 2010] Paper 2BQuestion: [APRIL, 2010] Paper 2B b. Explain how humus: ii) Improves the texture of a clay soil. (2) Humus helps soil particles stick together into larger crumbs.
    • Sandy Soil:Sandy Soil:  light soil  water drains quickly As water drains quickly TWO disadvantages result:
    • 1. Soil dries up quickly1. Soil dries up quickly Why is this a disadvantage for the farmer? Water is expensive!!
    • 2. S2. Salts are leached easilyalts are leached easily LeachingLeaching:: salts dissolve &salts dissolve & are lostare lost
    • Sandy Soil is improved by:Sandy Soil is improved by:  adding humus as this:- 1.holds more water 2.provides salts
    • Soil is composed of:Soil is composed of:  rock particles  humus  mineral salts  water  air  organisms
    • HumusHumus  a jam-like substance made up of decayed plants and animals  is found in the topsoil – blackish in colour
    • HumusHumus  if there is not enough oxygen, materials accumulate to form half decayed materials called peat  peat decays into humus if placed in well aerated soil
    • HumusHumus  helps to clump soil particles into crumbs
    • Humus improves soil by:-Humus improves soil by:-  providing mineral salts from decay by bacteria and fungi  providing air spaces  retaining water  improves crumb structure (prevents soil from being blown away)
    • Loam SoilLoam Soil  contains twice as much sand ascontains twice as much sand as clayclay Clay [1 part] Sand [2 parts] silt
    • How can youHow can you separate the soilseparate the soil particles as shownparticles as shown in the chart?in the chart?  add water  mix  leave to settle
    • ExperimentExperiment To find the components of soil.
    • To find the organic content of soil. ExperimentExperiment
    • percentage of organic matter = × loss in weight weight of original dry sample 100 Original weight: 105 g Final weight: 100 g Loss in weight: 5 g × = 5 100 4.8% 105
    •  rock particles  humus  mineral salts  water  air  organisms SOILSOIL
    • WaterWater  is found as thin films around soil particles  water moves upwards towards the surface by capillarity
    • To find the water content of soil. ExperimentExperiment
    • Precaution when heating soil:Precaution when heating soil: Temperature must NOT be more than 100°C. WHY?
    • × loss in weight original wet sample 100 Original wet weight: 200 g Final weight: 185 g Loss in weight: 15 g × = 15 100 7.5% 200 Percentage of water in soil:Percentage of water in soil:
    • SOILSOIL  rock particles  humus  mineral salts  water  air  organisms
    • 1. rock erosion 2. decay of dead organisms TWO sources of salts in soil:TWO sources of salts in soil:
    • Salinisation is a Soil ProblemSalinisation is a Soil Problem  often in arid and semi-arid areas (natural mineral salt conc. high) – The little precipitation that falls is quickly evaporated – Leaves behind salts  salt concentrations get to levels toxic to plants  gradual accumulation of salt in the soil, usually due to improper irrigation techniques
    • Many organisms bring aboutMany organisms bring about decay:decay:
    •  To compare the drainage of two soil samples. ExperimentExperiment
    • SOILSOIL  rock particles  humus  mineral salts  water  air
    • 1. roots for respiration Air is used by:Air is used by: 2. decomposers to decay material into humus
    • How can a farmer introduce air into the soil? A good soil has a lot of airA good soil has a lot of air spaces between the crumbsspaces between the crumbs
    • By ploughing
    •  To estimate the volume of air in a soil. ExperimentExperiment
    • Conclusion:  Air is important in soil for roots to respire and for decomposers to remain alive. ExperimentExperiment volume of air in soil percentage of air = volume of soil sample 100×
    •  rock particles  humus  mineral salts  water  air  organisms SOILSOIL
    • Bacteria & FungiBacteria & Fungi make salts available to plants
    • Earthworms improve soil by:Earthworms improve soil by: 1. their burrows they mix and loosen the soil and so help to drain and aerate it 2. providing salts due to their wastes and by pulling leaves into the soil
    • Earthworms improve soil by:Earthworms improve soil by: 3. making the soil alkaline as it passes through their intestine – bacterial growth is favoured by this pH
    • Earthworms improve soil by:Earthworms improve soil by: 4. binding soil particles together by the secretions from the intestines 5. making the soil finer – young roots can emerge easier
    • Harmful OrganismsHarmful Organisms  Nematodes can be harmful by:- 1.feeding on bacteria 2.being ectoparasites and pierce root 3.being endoparasites and damage roots and crops
    • Harmful OrganismsHarmful Organisms  various insect larvae eat the roots of plants e.g. wireworms (beetle larvae)
    • Soil fertility can be increasedSoil fertility can be increased by:by: 1. Adding fertilisers 2. Crop rotation 3. Ploughing 4. Keeping a neutral pH
    • Two types of Soil FertiliserTwo types of Soil Fertiliser 1. Natural fertilisers 2. Artificial / Chemical fertilisers
    • Natural FertilisersNatural Fertilisers Animal manure Compost
    • Why is the temperature at theWhy is the temperature at the centre of the compost pilecentre of the compost pile higher than ambienthigher than ambient temperature?temperature?
    • Heat released by microbes is difficult to be lost to the surroundings – far from surface. Cool air in Cool air in Warm air out
    • Advantages of NaturalAdvantages of Natural FertilisersFertilisers provide a wide variety of salts maintain the crumb structure long-lasting
    • Disadvantages of NaturalDisadvantages of Natural FertilisersFertilisers Salts are released slowly – decay is slow Bad smell Pests can grow in it
    • Artificial FertilisersArtificial Fertilisers Manufactured from chemical compounds
    • Advantages of ArtificialAdvantages of Artificial FertilisersFertilisers Salts are very soluble and are quickly available to the plant No pests in it No unpleasant smell
    • Disadvantages of ArtificialDisadvantages of Artificial FertilisersFertilisers salts are leached quickly destroy the crumb structure (soil becomes a powder)
    • Disadvantages of ArtificialDisadvantages of Artificial FertilisersFertilisers have less types of salts than manure no water-holding capacity
    • Explain why it is environmentallyExplain why it is environmentally sound to limit the use of artificialsound to limit the use of artificial fertilisers.fertilisers. Mobile- easily leach and pollute groundwater No water holding capacity (like organic)
    • Question: [SEP, 2011] Paper 2Question: [SEP, 2011] Paper 2 List TWO types of natural fertiliser. (2) 1. Compost / peat 2. Animal manure
    • Question: [MAY, 2011] Paper 1Question: [MAY, 2011] Paper 1 Give the biological explanation of the message in the following poster. (3)
    • Decomposers, consisting of bacteria and fungi, bring about the decay of the dead plant material. The decaying material is called compost and is vital for the growth of plants as mineral ions are released into the soil. Plants use nitrates, phosphates and other mineral salts to keep healthy.
    • Soil fertility can be increasedSoil fertility can be increased by:by: 1. Adding fertilisers 2. Crop rotation 3. Ploughing 4. Keeping a neutral pH
    • Crop rotationCrop rotation  means the planned order of specific crops planted on the same field  rotation may vary from 2 or 3 year or longer period  e.g. - wheat in autumn - root crop in summer - barley or oats in spring - leguminous plants (clover, peas)
    •  if the same crop is planted: certain salts are depleted
    • Benefits of CropBenefits of Crop rotationrotation 1. maintains crumb structure 2. supplies nitrates 3. reduces infection to plants as a pest cannot continue its life cycle if a different crop is planted
    • Soil fertility can be increasedSoil fertility can be increased by:by: 1. Adding fertilisers 2. Crop rotation 3. Ploughing 4. Keeping a neutral pH
    • Beneficial effects of ploughing:  makes soil porous so water drains better  introduces air into the soil
    • Beneficial effects of ploughing:  incorporates the residue from the previous crop into the soil  reduces the prevalence of weeds in the fields
    • THE ENDTHE END