Soil Soil Composition Soil - PowerPoint Presentation

Slide1

SoilSlide2

Soil

CompositionSlide3

Soil

Uppermost layer of earth’s crust that supports plants, animals and microbes

Soil Forming Factors

Parent MaterialTimeClimateVegetation & OrganismsTopographySlide4

1. Parent Material

Refers to the rock and minerals from which the soil derives.

The nature of the parent rock has a direct effect on the soil texture (think igneous vs sedimentary rocks)

Parent material may be native or transported to area by wind , water or glacier.Slide5

2. Time

After enough time, soil reaches maturity.

Depends on several factors

On average it takes 500 years to form 1 inch of soil. Slide6

3. Climate

Two most important factors that determine climate are

Temperature

and Moisture, they affectWeathering processesMicroenvironmental conditions for soil organismsPlant growthDecomposition ratesSoil pHChemical reactions in the soilSlide7

Formation of soil occurs

faster

in a climate with:

higher temperatures (increase the speed of the reaction)more rainfall (provides water for chemical reactions)Slide8

Weathering

Physical

includes temperature changes (freezing and thawing), crystal growth, pressure, plant roots, burrowing animals

causes disintegration of parent material and facilitates chemical weatheringChemicalalways in waterincludes hydration, hydrolysis, oxidation.examples :oxidation of Fe to form limoniteSlide9

4. Vegetation & Organisms

A single

teaspoonful

of soil is home to more than a billion organisms. Bacteria and protozoans – around 1 billionNematode worms—300Springtails—15Mites—20Pseudoscorpions—1Slide10

Larger Soil Organisms

Worms

– digest materials that make up humus and produce castings (amazing worm poo) and aerated soils with tunnels

Ants – aerate soils with tunnels and chambers, forage for food on surface and leave underground to decompose, bury seedsSlide11

Ecosystem Services

Soil organisms provide

ecosystem services

Important environmental benefits that ecosystems provide ExamplesDecaying and cycling organic materialPreventing soil erosionBreaking down toxic materialsCleansing waterSoil aeration (especially done by earthworms)Slide12

Symbiotic Relationships

Mycorrhizae

– fungus on the roots of some plants

Rhizobium – Soil bacteria that fix Nitrogen (remember them?... )Found on Legumes (peas, clover, peanuts etc…) NOT ON potatoes!Helps plants absorb essential nutrient minerals from the soilMycelium – threadlike body of the fungus (extends beyond the roots)Slide13

5. Topography

Physical characteristics of location where soil is formed.

Drainage

Slope directionElevationWind exposureSlide14

Soil Composition

Mineral Particles (45%)

Weathered rock

Provides essential nutrients for plantsOrganic Material (5%)Litter, animal waste, dead remains of plants and animals, humus (picture)Water (25%)Air (25%) Slide15

Texture of Soil

Relative proportion of sand, silt and clay determines

TEXTURE

Soil textures are produced by the combination of SandSilt ClaySlide16

Sand

- Basketball

Biggest

Can feel individual particles Silt - softballClay- tip of your penSmallestCan NOT feel individual particles (think baby powder)Slide17
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Spaces in the Soil

40-60% of volume of soil is normally

pore space

(space in between the grains)Spaces allow water and air to travel through soil.Plant roots growing in the soil need air Slide19

Permeability

The rate at which water (and air) moves from upper to lower soil layers.

Amount of room between grains (pore spaces) determines this

Larger pore spaces drain water quicklySmaller pore spaces tend to hold water and drain much slowerSlide20

“Large”

High permeability

Low permeability

Water

Water

Clay

“Small”

Silt

“Medium”

SandSlide21

Loam

Soils made of a mixture of:

Sand

SiltClay~40% sand~40% silt~20% claySlide22

Soil Textural Triangle

What type of soil am I?

55% sand

5% silt40% claySlide23

Soil Textural Triangle

What type of soil am I?

20% sand

75% silt5% claySlide24

Soil Properties

Soil texture affects soil properties

Coarse textured soil (sandy)

Large Pore SpacesWill not hold water well- flows through easilyFine textured soil (high in clay)Small Pore SpacesPoor drainageLow oxygen levels in soilDue to negatively charged surface, able to hold onto important plant nutrients (K+, Ca2+, NO2-)Slide25
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Soil

Nutrients & LayersSlide27

Soil pH

The pH of most soils ranges from 4.0 to 8.0.

But, the soil of the Pygmy Forest in California is extremely acidic (2.8-3.9) and in Death Valley, California, it is very basic (10.5).

Proper pH directly affects the availability of plant food nutrientsSlide28

pH

Too acidic or basic will not

Allow compounds to dissolve

Allow presence of certain ionsIf soil is too acidic, add ground limestoneIf soil is too basic, add organic material like cow manureSlide29

Soil Nutrients

Macronutrients

Larger in atomic structure. Ex. Nitrogen (N), Phosphorus (P) & Potassium (K).

MicronutrientsThese are smaller in atomic structure. Plants need them in small amounts. Ex. Selenium, Zinc & Iron.Slide30

Nitrogen Content

Stimulates above ground growth

Produces rich green color

Influences quality and protein content of fruit A plant’s use of other elements is stimulated by presence of NReplenished naturally by rhizobium on legume rootsFertilizer from manure or Chemicals Slide31

Phosphorus for Growth

Abundant in

Strong root system

Increases seed yield and fruit developmentParts of root involved in water uptake (hairs)Fertilizer is made from rock phosphate (remember the phosphorus cycle does not cycle through the atmosphere)Slide32

Potassium Content

Potash

Important in vigor and vitality of plant

Carries carbohydrates through the plantImproves color of flowersImproves quality of fruitPromotes vigorous root systemsOffsets too much NFound naturally in feldspar and mica rocksSlide33

Soil Horizons

O

- Rich in organic material

A - TopsoilE – Heavily leached (not always present)B - Lighter colored subsoilC - Weathered parent materialSlide34

Organic Layer (O-horizon)

The uppermost layer; it is rich in organic material.

Plant litter accumulates in the O-horizon and gradually decays.

In desert soils the O-horizon is completely absent, but in certain organically rich soils it may be the dominant layer.Slide35

Topsoil (A-horizon)

It is dark and rich in accumulated organic matter and humus.

It has a granular texture and is somewhat nutrient-poor due to the loss of many nutrient minerals to deeper layers and by leaching.Slide36

Subsoil (B-horizon)

The light-colored subsoil beneath the A-horizon; it is often a zone of illuviation where nutrient minerals have leached out of the topsoil and litter accumulate.

It is typically rich in iron and aluminum compounds and clay.Slide37

Parent Material (C-horizon)

This contains weathered pieces of rock and borders the un-weathered solid parent material (R Layer) .

Most roots do not go down this deep and it is often saturated with groundwater.Slide38

Soil

ProblemsSlide39

Soil Problems

Soil Erosion

Wearing away or removal of soil from the land

Caused primarily by water and windWhy a problem?Causes a loss in soil fertility as organic material and nutrients are erodedMore fertilizers must be used to replace nutrients lost to erosionAccelerated by poor soil management practicesSlide40

Very severe

Severe

Moderate

Soil ErosionSlide41

Soil is eroding faster than it is forming on more than one-third of the world’s cropland.Slide42

Salinization & WaterloggingSlide43

Soil Salinization

Gradual accumulation of salt in the soil, usually due to improper irrigation techniques

Often in arid and semi-arid areas

The little precipitation that falls is quickly evaporatedLeaves behind saltsSalt concentrations get to levels toxic to plantsSlide44

Desertification

Degradation of once-fertile rangeland, agricultural land, or tropical dry forest into nonproductive desert

Typically a human-induced condition

Change in vegetation changes climate, further decreasing precipitation levels (usually in a positive feedback loop scenario)Asia and Africa – largest areas – many droughtsSlide45

American Dust Bowl

Great Plains have low precipitation and subject to drought

1930-1937 severe drought

No natural vegetation roots to hold soil in placeNative vegetation replaced by annual cropsWinds blew soil as far east as NYC and DC.Farmers went bankruptSlide46

Soil Conservation Policies in US

Soil Conservation Act 1935

Authorized formation of Soil Conservation Service, now called Natural Resource Conservation Service (NRCS)

Assess soil damage and develop policies to improve soilFood Security Act (Farm Bill) 1985Required farmers with highly erodible soil had to change their farming practicesInstituted Conservation Reserve Program (CRP)Pays farmers to stop farming highly erodible landSlide47

Soil Conservation Practices

Conservation Tillage

Residues from previous year’s crops are left in place to prevent soil erosion

Includes no till agricultureSlide48

Soil Conservation Practices

Crop Rotation

Planting a series of different crops in the same field over a period of years

Lessens pest and insect diseaseLets nutrients specific for certain plants naturally replenishSlide49

Soil Conservation Practices

Contour Plowing

Plowing around hill (following natural contour of land) instead of up-down

Decreases soil erosionSlide50

Soil Conservation Practices

Strip Cropping

Alternating strips of different crops along natural contoursSlide51

Soil Conservation Practices

Terracing

Creating terraces on steep slopes to prevent erosionSlide52

Soil Conservation Practices

Agroforestry

Trees and crops are planted together to improve soil fertility in degraded soils

Trees grow much longer and provide many soil benefits: - reduces soil erosion - regulates water - provides habitat for natural enemies of crop pests - leaf litter regenerates soil - shadeExample: Acacia trees and millet Slide53

Soil Reclamation

Two steps

Stabilize land to prevent further erosion

Restoring soil to former fertilityBest way to do this is to plant shelterbeltsRow of trees planted to reduce wind erosion of soil