Chapter 14 Soil Resources

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

Rock 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

THE ROCK CYCLE !

EXAMPLES OF METAMORPHIC ROCK

Soil Holds nutrients and water IT TAKES A YEAR TO MAKE 1 mm TOPSOIL 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

Soil Formation 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)

PERCENTS ARE FOR A TYPICAL/HEALTHY SOIL Soil Composition 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

Soil Composition Pore space air- good for aeration (O2, CO2, N2) water- provides water to roots

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

Soil Organisms There are millions of microorganisms in 1 tsp of fertile agricultural soil

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

Nutrient Cycling Nutrients are cycled between plants, organisms and soil Example Bacteria and fungi decompose plant and animal wastes They are transformed into CO2, soil nutrients and water

Soil Properties - physical 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)

Soil Properties - physical 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+, Ca2+) Poor drainage Low oxygen levels in soil

Soil Properties - physical

Soil Properties - physical Loam Combo all textures – 20% clay, 40% sand and silt Ideal for agriculture Sand holds air/water Clay holds nutrients

Soil Properties - chemical 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

Re-group Physical and chemical properties of soil Soil vocab: clay, silt, sand, loam, humus, topsoil

Soil examples coniferous forests O-horizon composed of needles Not good farmland- too acidic

Soil examples 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

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

Soil examples arid regions Low precipitation = no leaching, no vegetation = not much org. matter

Soil examples 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

Soil Problems Soil Erosion Why a problem? 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

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

Case in Point: American Dust Bowl 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

Soil Problems Nutrient Mineral Depletion

Soil Problems Soil Salinization Often in arid and semi-arid areas 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

Soil Problems Desertification Typically a human-induced condition 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)

Soil Conservation Conservation Tillage Crop Rotation (polyculture) Residues from previous year’s crops are left in place to prevent soil erosion Includes no tillage Con: weeds 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)

Contour Plowing Strip Cropping Terracing Soil Conservation – farming on SLOPES – need to slow water run-off to prevent erosion. Strip Cropping 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 Terracing

Preserving Soil Fertility 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

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

Soil Conservation Policies in US Food Security Act (Farm Bill) 1985 Required farmers with highly erodible soil to incorporate erosion-control practices or are at risk of losing subsidies

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?

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?

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?

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

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?

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?

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?

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?

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?