1. AP Environmental Science Soil Resources (Ch 14) Living in the Environment, 14th edition, G. Tyler Miller

2. Soil Characteristics
Understand what soil is and how it forms. Compare and contrast the characteristics of different soils. What type do you have around your house?
1) clay = “layer silicates that are formed as products of chemical weathering of other silicate minerals at the earth's surface. They are found most often in shales, the most common type of sedimentary rock.”
2) silt = rock worn into tiny pieces (coarser than clay, but finer than sand). usually 1/20 millimeter or less in diameter
3) sand = quartz or silica worn down over time. grains with diameters between 0.06 mm to 2 mm
4) organic matter (humus)
5) Loam = soil containing a mixture of clay, sand, silt and humus. Good for growing most crops.

3. Soil Porosity and Permeability
Porosity - volume of water that “fits between” the soil particles
Permeability - rate of flow of water through soil
% retention - how much water is “trapped” by soil
Porosity and Permeability are directly related; when one is high, the other is high as well. % water retention is inversely related to both.
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1) Clay -  porosity  permeability,  retention
2) Silt -  porosity,  permeability, retention
3) Sand -  porosity,  permeability,  retention
4) Organic matter -  porosity,  permeability,  retention

4. Soil Horizons

6. Soil Horizons

7. Soil Conservation
Explain what soil erosion is. Describe its causes and effects. List and describe various soil conservation methods.
Soil moves….due to water, wind, people
Loss of topsoil…the most fertile
Soil ends up as sediment in water
Soil IS renewable…WHERE does it come from?

8. Irrigation

9. Salinization & Waterlogging

10. Salinization & Waterlogging

11. Desertification

12. List and describe some of the pros and cons of using fertilizers
List and describe some of the pros and cons of using fertilizers. What different sorts of fertilizers are available?
Organic…
manure adds N and soil bacteria & fungi
green manure
compost
mushroom spores
Inorganic…1/4th of the world’s crops depend on this.
N, K, P
Experimental data comparing methods!
Click on the picture!

13. Soil Formation
Soil formation - Parent material is slowly broken down by biological, chemical and physical weathering.
Biological - Respiration of plant roots and other organisms produce CO2, which reacts with soil water to produce carbonic acid (H2CO3).
Chemical - Acids crack rocks  water seeps in  breaks down particles.
Physical - Weathering introduces water that breaks down particles.
Time scale - Formation of 2.5 cm of topsoil takes yrs.

14. Soil Formation

15. Soil Composition Soil Composition
45% Mineral particles (broken down pieces of rock)
5% Organic matter (humus - from dead organisms, worm castings, leaf litter)
25% Water (precipitation)
25% Air (More with sandy soil, less with clay soil)
Soil organisms - Millions in one teaspoon of fertile agricultural soil!
- bacteria, fungi, algae, microscopic worms.
provide ecological services such as worm castings, decomposition to humus, breaking down of toxic materials, cleansing water, nutrient cycling from decomposers or upon death

16. Soil Texture Loam - ideal agricultural soil
40% sand (larger - structural support, aeration, permeability)
40% silt (smaller - holds nutrient minerals and water)
20% clay (even smaller - holds nutrient minerals and water)
Plants grown in sandy soils
More susceptible to mineral deficiencies and drought
Plants grown in clay soils
More susceptible to waterlogging, and oxygen depletion (think small pore size, low porosity)

17. Soil Texture Triangle

18. Soil Acidity (pH) pH - concentration of H+ ions
Scale - From 0 (very acidic) to 14 (very basic, or alkaline)
pH of most healthy soils
pH matters because it affects solubility of nutrient minerals
Aluminum and Manganese are more soluble in low pH - roots sometimes absorb too much (toxic levels)
Soil pH affects leaching - high pH increases leaching of important ions such as K+
Causes of changes - acid rain, decomposition, leaf litter, mining (acid sulfate soils)
Remediation
- Too high pH, add acidic leaf litter
- Too low pH, add lime

19. Soil Nutrients

20. Soil Nutrients (NPK)
Organic - animal manure, bone meal, compost (slow-acting, long-lasting)
Delay in availability to plants, needs time for the organic material to decompose
Delay causes low level of nutrient leaching
Improves water holding capacity
Inorganic - Manufactured from chemical compounds (fast-acting, short-lasting)
Highly soluble so immediately available to plants
High solubility also makes it leach quickly (pollutes water)
Suppresses growth of microorganisms
Source of nitrogen gases that increase air pollution
Production requires much energy from fossil fuels, increasing CO2 emissions.