lesson 6 soil. think about it… can plants be grown in pure sand?
TRANSCRIPT
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.