2CHAPTER TOPICS Rock cycle Soil formation Soil composition Physical and chemical properties of soilMain soil typesErosion and other soil problemsSoil conservation
3Rock groups: igneous, sedimentary, metamorphic Igneous – from melted rock that has cooled/solidified (Ex. granite)Rarely has fossils, crystalsSedimentary – formed on surface (land/water) from layered sediment broken from rock (Ex. limestone, shale)Most rock, fossils, visible layersMetamorphic – other rock that changes due to heat/pressure (ex. slate and marble)Rarely has fossils, may have layered crystals
6Soil Holds nutrients and water IT TAKES A YEAR TO MAKE 1 mm TOPSOILHolds nutrients and waterCleanses and filters water as it flows through soilAffects the amount of water that returns to atmosphereNamed for physical and chemical propertiesEX: texture, pH
7Soil FormationFormed from weathering, takes TIME (rocks broken into smaller and smaller bits)Physical weathering – alternate freezing and thawing, wind/water erosion, ocean wavesChemical weathering – carbonic acid in soil (from CO2 and H2O)Biological weathering – lichen produce acidseveral factors influence the soil formed:Parent material – rock/mineral it came fromLiving organisms – decompose litter and recycle nutrients (Ex. Rhizobium, fungi, insects, worms, snails)
8PERCENTS ARE FOR A TYPICAL/HEALTHY SOIL Soil Composition1. Mineral Particles (45%)Weathered rockProvides essential nutrients for plants2. Organic Material (5%)Litter, animal dung, dead remains of plants and animalsIncrease water-holding capacityHumus – decomposed org. matter, binds nutrients/water3. Water (25%)4. Air (25%)PERCENTS ARE FOR A TYPICAL/HEALTHY SOIL
17Soil Properties - physical Soil texture affects soil propertiesCoarse textured soil (sandy)Will not hold water well- flows through easilyFine textured soil (high in clay)Due to negatively charged surface, able to hold onto important plant nutrients (K+, Ca2+)Poor drainageLow oxygen levels in soil
20Soil Properties - physical LoamCombo all textures – 20% clay, 40% sand and siltIdeal for agricultureSand holds air/waterClay holds nutrients
21Soil Properties - chemical Nutrients: Nitrogen, potassium (potash), phosphorusSoil AcidityMeasured using pH scale0-7 = acidic ; 7 = neutral ; 7-14 = basicpH of most soils range from 4-8Affects solubility of certain plant nutrientsAffects leaching of nutrient mineralsEx: acidic soil doesn’t bind positive ions as wellOptimum soil pH is 6-7plant nutrients are most available to plantsSoil amendments (ex: lime) can be used to achieve this pH
22Re-group Physical and chemical properties of soil Soil vocab: clay, silt, sand, loam, humus, topsoil
23Soil examples coniferous forests O-horizon composed of needles Not good farmland- too acidic
24Soil examples Temperate Deciduous Forests Precipitation high enough to leach most organics and nutrients out of O-, A- and B-horizonsSoil fertility maintained by leaf litter
25Soil examples temperate, semi-arid grassland Very fertile soil Soluble nutrients stay in A-horizon due to low leaching
26Soil examples arid regions Low precipitation = no leaching, no vegetation = not much org. matter
27Soil examples tropical and subtropical areas with high precipitation Very little organic material accumulation due to fast decay rateB-horizon is highly leached, acidic, and nutrient poorNutrient minerals in plants, not soil
28Soil Problems Soil Erosion Why a problem? Def: wearing away of soil from the landCaused primarily by water and windWhy a problem?less soil grow less plantsDecrease amount of nutrients need more fertilizersSediment into surface water that decreases quality of fish habitat
29Soil Problems Erosion causes: natural, but anthropogenic activities make it worse:Poor agricultural practicesRemoving natural plant communities when building roads (plant cover holds soil)overgrazing
30Case in Point: American Dust Bowl Great Plains have low precipitation and subject to droughtsevere droughtNo natural vegetation roots to hold soil in placeReplaced by annual cropsWinds blew soil as far east as NYC and DC.Farmers went bankrupt
33Soil Problems Soil Salinization Often in arid and semi-arid areas Def: gradual accumulation of salt in the soilOften in arid and semi-arid areasThe little precipitation that falls is quickly evaporatedLeaves behind saltsmost plants dieSoil remediationDilution, bioremediation/phytoremediation
34Soil Problems Desertification Typically a human-induced condition Def: degradation of once-fertile land into nonproductive desertTypically a human-induced conditionEx: African Sahel; possible solution: Agroforestry to plant crops and Acacia trees (nitrogen-fixing + decomposing leaves)
35Soil Conservation Conservation Tillage Crop Rotation (polyculture) Residues from previous year’s crops are left in place to prevent soil erosionIncludes no tillageCon: weedsCrop Rotation (polyculture)Planting a series of different crops in the same field over a period of yearsLessens pest and insect diseaseReplenish nitrogenEx: corn soybeans oats alfalfa (soy and alfalfa = legumes)
36Contour Plowing Strip Cropping Terracing Soil Conservation – farming on SLOPES – need to slow water run-off to prevent erosion.Strip CroppingContour PlowingPlowing around hill instead of up-downRows catch waterStrip CroppingAlternating strips of different crops on steep slopes ; prevents erosion by naturally damming waterTerracingCreating terraces on steep slopes to prevent erosionTerracing
37Preserving Soil Fertility Organic fertilizersAnimal manure, crop residue, worm castings, and compost (individual and municipal)Nutrients available only as material decomposesSlow acting and long lastingCould contain disease-causing pathogens if not properly composted.Inorganic fertilizersMade from chemical compoundsSolubleFast acting, short lastingBad for environmentleach and pollute groundwater and surface run-offProduced using lots of fossil fuels
39SOIL SUSTAINABILITYUse soil without depleting fertility and amount so it’s productive enough for future generations
40Soil Conservation Policies in US Food Security Act (Farm Bill) 1985Required farmers with highly erodible soil to incorporate erosion-control practices or are at risk of losing subsidies
41What 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?
42Having 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?
43What 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?
44Does rain affect leaching? Other than organic matter and inorganic particles, what else constitutes soil?What does anthropogenic mean?What does sustainable mean?
45In 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?
46Name the 3 types of rockWhich 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?
47Granite 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?
48How 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?
49What 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?