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 Rock cycle  Soil formation  Soil composition  Physical and chemical properties of soil  Main soil types  Erosion and other soil problems  Soil.

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Presentation on theme: " Rock cycle  Soil formation  Soil composition  Physical and chemical properties of soil  Main soil types  Erosion and other soil problems  Soil."— Presentation transcript:


2  Rock cycle  Soil formation  Soil composition  Physical and chemical properties of soil  Main soil types  Erosion and other soil problems  Soil conservation

3  groups: igneous, sedimentary, metamorphic  Igneous – from melted rock that has cooled/solidified (Ex. granite)  Rarely has fossils, crystals  Sedimentary – formed on surface (land/water) from layered sediment broken from rock (Ex. limestone, shale)  Most rock, fossils, visible layers  Metamorphic – other rock that changes due to heat/pressure (ex. slate and marble)  Rarely has fossils, may have layered crystals



6  Holds nutrients and water  Cleanses and filters water as it flows through soil  Affects the amount of water that returns to atmosphere  Named for physical and chemical properties  EX: texture, pH IT TAKES A YEAR TO MAKE 1 mm TOPSOIL

7 TIME  Formed from weathering, takes TIME (rocks broken into smaller and smaller bits)  Physical weathering – alternate freezing and thawing, wind/water erosion, ocean waves  Chemical weathering – carbonic acid in soil (from CO2 and H2O)  Biological weathering – lichen produce acid  several factors influence the soil formed:  Parent material – rock/mineral it came from  Living organisms – decompose litter and recycle nutrients (Ex. Rhizobium, fungi, insects, worms, snails)

8 1. Mineral Particles (45%)  Weathered rock  Provides essential nutrients for plants 2. Organic Material (5%)  Litter, animal dung, dead remains of plants and animals  Increase water-holding capacity  Humus – decomposed org. matter, binds nutrients/water 3. Water (25%) 4. Air (25%) PERCENTS ARE FOR A TYPICAL/HEALTHY SOIL


10  Pore space  air- good for aeration (O 2, CO 2, N 2 )  water- provides water to roots

11  O-horizon  Rich in plant litter/organic matter  A-horizon  Topsoil (organic matter and humus), plant growth, leached EE  B-horizon  Lighter colored subsoil, illuviation, high inorganic  C-horizon  Somewhat weathered parent material, groundwater, no organic  Bedrock - unweathered

12  There are millions of microorganisms in 1 tsp of fertile agricultural soil

13  Soil organisms provide ecosystem services  Examples  Decaying and cycling organic material  Breaking down toxic materials  Cleansing water  Soil aeration (especially done by earthworms)

14  Nutrients are cycled between plants, organisms and soil  Example  Bacteria and fungi decompose plant and animal wastes  They are transformed into CO 2, soil nutrients and water

15  Soil Texture  Relative proportion of sand, silt and clay  Sand: 2mm-0.05mm (large)  Silt: 0.05mm-0.002mm (medium)  Clay: less than 0.002mm (small)


17  Soil texture affects soil properties  Coarse textured soil (sandy)  Will not hold water well- flows through easily  Fine textured soil (high in clay)  Due to negatively charged surface, able to hold onto important plant nutrients (K +, Ca 2+ )  Poor drainage  Low oxygen levels in soil



20  Loam  Combo all textures – 20% clay, 40% sand and silt  Ideal for agriculture ▪ Sand holds air/water ▪ Clay holds nutrients

21  Nutrients: Nitrogen, potassium (potash), phosphorus  Soil Acidity  Measured using pH scale ▪ 0-7 = acidic ; 7 = neutral ; 7-14 = basic  pH of most soils range from 4-8  Affects solubility of certain plant nutrients  Affects leaching of nutrient minerals ▪ Ex: acidic soil doesn’t bind positive ions as well  Optimum soil pH is 6-7 ▪ plant nutrients are most available to plants ▪ Soil amendments (ex: lime) can be used to achieve this pH

22  Physical and chemical properties of soil  Soil vocab: clay, silt, sand, loam, humus, topsoil

23  coniferous forests  O-horizon composed of needles  Not good farmland- too acidic

24  Temperate Deciduous Forests  Precipitation high enough to leach most organics and nutrients out of O-, A- and B- horizons  Soil fertility maintained by leaf litter

25  temperate, semi-arid grassland  Very fertile soil  Soluble nutrients stay in A-horizon due to low leaching

26  arid regions  Low precipitation = no leaching, no vegetation = not much org. matter

27  tropical and subtropical areas with high precipitation  Very little organic material accumulation due to fast decay rate  B-horizon is highly leached, acidic, and nutrient poor  Nutrient minerals in plants, not soil

28  Soil Erosion  Def: wearing away of soil from the land  Caused primarily by water and wind  Why a problem?  less soil  grow less plants  Decrease amount of nutrients  need more fertilizers  Sediment into surface water that decreases quality of fish habitat

29  Erosion causes:  natural, but anthropogenic activities make it worse: ▪ Poor agricultural practices ▪ Removing natural plant communities when building roads (plant cover holds soil) ▪ overgrazing

30  Great Plains have low precipitation and subject to drought  1930-1937 severe drought  No natural vegetation roots to hold soil in place ▪ Replaced by annual crops  Winds blew soil as far east as NYC and DC.  Farmers went bankrupt


32  Nutrient Mineral Depletion

33  Soil Salinization  Def: gradual accumulation of salt in the soil  Often in arid and semi-arid areas  The little precipitation that falls is quickly evaporated  Leaves behind salts  most plants die  Soil remediation  Dilution, bioremediation/phytoremediation

34  Desertification  Def: degradation of once-fertile land into nonproductive desert  Typically a human-induced condition  Ex: African Sahel; possible solution: Agroforestry to plant crops and Acacia trees (nitrogen-fixing + decomposing leaves)

35  Conservation Tillage  Residues from previous year’s crops are left in place to prevent soil erosion  Includes no tillage  Con: weeds o Crop Rotation (polyculture) Planting a series of different crops in the same field over a period of years Lessens pest and insect disease Replenish nitrogen Ex: corn  soybeans  oats  alfalfa (soy and alfalfa = legumes)

36  Contour Plowing  Plowing around hill instead of up-down  Rows catch water  Strip Cropping  Alternating strips of different crops on steep slopes ; prevents erosion by naturally damming water  Terracing  Creating terraces on steep slopes to prevent erosion Strip Cropping Terracing

37  Organic fertilizers  Animal manure, crop residue, worm castings, and compost (individual and municipal)  Nutrients available only as material decomposes ▪ Slow acting and long lasting ▪ Could contain disease-causing pathogens if not properly composted.  Inorganic fertilizers  Made from chemical compounds  Soluble ▪ Fast acting, short lasting  Bad for environment ▪ leach and pollute groundwater and surface run-off ▪ Produced using lots of fossil fuels


39  Use soil without depleting fertility and amount so it’s productive enough for future generations

40  Food Security Act (Farm Bill) 1985  Required farmers with highly erodible soil to incorporate erosion-control practices or are at risk of losing subsidies

41  What physical test could you do to soil?  What chemical test could you perform on soil?  What are the layers of soil horizons, but top down?  What is the ideal pH for most plants?

42  Having a pH lower than 7 makes a substance a ____.  What is loam?  Why does clay bind readily to some ions?  What inorganic soil particle is the largest?  What inorganic soil particle is the smallest?

43  What happens to the quantity of organic material as you move down the horizons?  Which soil horizon is the illuviation zone?  Which soil horizon is where the topsoil is located?  What does leaching mean?

44  Does rain affect leaching?  Other than organic matter and inorganic particles, what else constitutes soil?  What does anthropogenic mean?  What does sustainable mean?

45  In typical soil, is there more organic matter or inorganic particles?  Why is air space important for soil?  What is humus?  What part of soil increases its water holding capacity?  Where do the inorganic particles of soil come from?

46  Name the 3 types of rock  Which rock is from cooled lava?  Which rock forms from layer upon layer of other rock particles and dead organisms?  What rock forms when either of the other 2 are exposed to high heat and pressure enough to change them?

47  Granite is an example of what type of rock?  Marble is an example of what type of rock?  Limestone and sandstone are examples of what type of rock?  Why is soil important?  What are the 3 types of weathering processes?  What role do earthworms play in forming soil?

48  How does carbonic acid form?  What does it do to rock?  Give an example of physical weathering.  Give an example of biological weathering.  Where is bedrock located?

49  What are the consequences of erosion?  What are causes of erosion?  What is desertification?  What is soil salinization?  How do you remedy it?  What causes it?

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