Lesson 6

Soil

Think About It…

Can plants be grown in pure sand?

Focus Question…

How does soil form and how can it be preserved?

Development of Soil…

1. What is the first step in soil formation? The weathering of rocks

Weathered rocks and the Koevals!

Development of Soil…Mosses and lichens are

called pioneer organisms because they are the first organisms to grow on rocks

Development of Soil…2. What is the second step in soil formation? the addition of humus (decaying organic matter)

Soil Profile – Draw this!1. A soil profile is a cross

section of soil.2. There are three major soil

horizons – A, B, and C.

a. Horizon A – top & darkest layer (high concentration of organic matter - humus)

b. Horizon B – subsoil enriched with clay minerals leached from the topsoil.

c. Horizon C – bottom layer (weathered rock)

Factors Affecting Soil Profiles

1. Topography (slope) of the land –

a.Soils on slopes tend to be thinner

b.soils in flat areas like valleys or plains are thicker

2. Age – older soils are thicker because they have had more time to develop.

3. Climate – See next few slides…

Climate Affects Soil: Tropical Soil

a. Tropical Soil…– Is intensely

weathered (and often infertile) soil because of …high temperatures and heavy rainfall

– Can only be farmed for a few years

http://www.clas.ufl.edu/users/azimmer/photogallery/PeruSciPhotos/ps5.JPG

Climate Affects Soil : Desert Soil

b. Desert soil…– Is light-colored

with a thin A horizon b/c…

–contains little or no organic matter b/c there is very little rain.

www.lpi.usra.edu/science/treiman/greatdesert/workshop/desertsoil/desertsoil_imgs/p7184692m.jpg

Cryptobiotic Crust – Don’t Bust the Crust!

http://helios.bto.ed.ac.uk/bto/microbes/bootcrus.jpg

http://www.gatewaytosedona.com/imagebin/gwsites/gwsedona/department/10/crust_300.jpg

Climate Affects Soil : Polar Soilc. Polar Soil has

permanently frozen soil (permafrost) b/co It forms at

high latitudes and elevations so it is always cold!

o Can not support the growth of trees (tundra)

Climate Affects Soil: Temperate Soild. Temperate soil is

rich and thick and very fertile because it forms in flat

areas over a long period of time

– Includes grasslands, forests, prairies

– Our grains are grown here!

•http://www.blueplanetbiomes.org/images/grasslands_lrg.jpg

Distribution of Soil Typeshttp://soils.ag.uidaho.edu/soilorders/i/worldorders.jpg

Soil Textures 1. Particles of soil are classified

by size.

2. The particles of soil are…

clay, silt, & sand.

3. What determines a soil’s texture

The relative proportions of these particles.

4. The texture of a soil affects

its capacity to absorb and retain water & support plant growth.

http://wps.prenhall.com/wps/media/objects/1411/1445480/FG12_15_wo_arrows.JPG

Soil Texture Triangle

Soil Fertility…1. Soil fertility is the measure of a

soil’s ability to grow plants.

2. Farmers use fertilizer to… replace nutrients & grow more food.

a. Inorganic fertilizer is made in factories.

b. There are 2 disadvantages:

1. requires energy to make it.

2. too expensive for poor farmers.

It is used in conventional farming

http://www.bdembjp.com/images/chittagongUrea.JPG

Fertilizer factory in Japan

2b. Natural, Organic Fertilizer…

2b. Examples: compost (plants) and manure (animal waste)

The advantage of using organic fertilizers…

… adds humus and moisture to the soil

Manure-spreading Truck

Soil Fertility - Legumes 3. The planting of legumes

– peas, beans - and clover – allows bacteria to grow on plant roots and replace nitrates in the soil.

4. Nitrogen-fixing bacteria… get nitrogen (N) from the air and “fix” it into fertilizer.

Remember this for your lab!!

http://www.iger.bbsrc.ac.uk/Research/Departments/SEES/Teams/images/legume-roots.jpg

Note the nodules on the roots – these contain colonies of

nitrogen-fixing bacteria.