SOILS

1. SOILS

2. What is Soil?? Soils are the transition between the biotic and abiotic worlds. Soil is a mixture of: • Minerals • Water • Gases • HUMUS-Dead “things” that have broken down and become organic material—decayed plant and animal remains (thanks to decomposing fungi and bacteria)

3. Soil Composition (idealized)

4. Why are soils important? Soils are important: • As a habitat for growing crops • Food • Fabrics/Dyes • Rubber/Building Materials • Medium for photosynthetic organisms • Medium for decomposers • As foundations of buildings • As beds for roads and highways • As an absorbent of domestic wastes in rural areas as well as a depository for other wastes • As a filter for pollution that comes from rain and water runoff

5. What determines how soil forms? There are THREE main contributing factors • Length of time soils have been developing—the AGE of the soils • The materials (rocks) from which they form- these are called PARENT MATERIAL • The ENVIRONMENT in which they developed (climate, vegetation, soil life, topography) Good rule of thumb: 500-1000 yrs per inch of topsoil

6. How do parent materials get into soils?? WEATHERING: Any process where rock breaks down (changes chemically and physically) There are two types of weathering: Physical or Mechanical Weathering: Large rock mass is broken into smaller fragments of the same type-NO CHEMICAL CHANGE Chemical Weathering: mass of rock is decomposed by chemical reactions

7. What is happening in these photos?

8. Let’s take a closer look at frost wedging… • Water collects in cracks in rock • Water expands when it freezes • Water melts; Pieces of rock break off Rock

9. Chemical Weathering • Most chemical weathering involves gases in the atmosphere (oxygen, carbon dioxide, acid gases) and/or water Example: Think about metal rusting • You go from metal to rust—a chemical reaction has taken place Contrast with EROSION (movement!) by wind, water, ice

10. Topsoil Formation

11. Detritus-based Soil Ecosystem All these happy little critters break down dead plant and animal material and aerate the soil—they make topsoil!

12. What is a soil profile?

13. Soil Profiles • Soil Profiles - the sequence of layers (horizons) from the surface downward to rock or other underlying material Soil Layers - “O”- organic horizons, litter derived from dead plants and animals - A- TOPSOIL horizons which lie at or near the surface [Eluvial- Characterized as zones of maximum leaching, E = Exit] - B- SUBSOIL [sometimes illuvial I = Into] - C- unconsolidated parent material under A&B layers - Bedrock

14. Soil profile example Maryland Soil Profile

15. What are some soil properties? • Porosity • Permeability • Texture • pH • Nutrient Levels—Nitrogen/Phosphorus • Color

16. Soil Porosity and Permeability • Porosity- volume of pores (spaces) per volume of soil—sometimes referred to as “aeration” • Permeability- rate of flow of materials through soil • Infiltration—water getting into soil

17. SOIL TEXTURE • Soil texture: The way a soil "feels" Depends on the fraction of each size of particle in the soil • Sand, silt, and clayare names that describe the size of individual particles in the soil. • SANDare the largest particles and they feel "gritty.“ • SILTare medium sized, and they feel soft, silky or "floury" • CLAYare the smallest sized particles, and they feel "sticky" and they are hard to squeeze.

18. Why care about soil texture? Predicts soil properties-fertility, drainage, etc. LOTS! • Sandy soils • low organic matter • Poor retention water and nutrients (it flows through) • As silt and clay fractions increase, • More organic matter • Better buffered • Better retention of water and nutrients • But you can have TOO much clay • Hard to cultivate-too sticky when wet; too hard when dry • Shrinks and swells The best soils are a mix of all three (20% clay, 40% sand, 40% silt) and are called LOAM

19. Soil pH What does pH measure? • It’s a measure of how acidic or basic of a solution is on a 0 to 14 scale (REM: inverse log of [H+]?) • We actually measure pH of soil SOLUTION • The pH of the soil solution affects how much of soil nutrients are available to plants. TOO ACID or TOO BASIC, can cause important nutrients (like nitrogen and phosphorus) to be unavailable. • At these extremes (too acid and too basic), METALS also released into soil, causing TOXIC effects in plants • PESTICIDE TIE-IN: If soil is too acidic, applied pesticides, herbicides, and fungicides will not be absorbed (held in the soil) and they will end up in runoff

20. Plant pH Preferences

21. Soil Nutrients • Nutrients: essential chemical elements needed for the growth of healthy plants • Plants get nutrients from soil after the nutrients have dissolved in the soil solution (the water around soil particles) • Each nutrient has specific roles in producing healthy plants • Nitrogen • Phosphorus

22.  Needed for chlorophyll, growth Low nitrogen causes yellowy leaves Needed for roots, energy  Low phosphorus causes purply leaves, poor roots

24. Sources of Images • GLOBE Program- Agricultural Soils http://ltpwww.gsfc.nasa.gov/globe/agrisoil.htm http://ltpwww.gsfc.nasa.gov/globe/basics.htm • http://mather.ar.utexas.edu/AV/CRP369K/Lectures/Soils.pdf • http://gushwalogy.org/APES/EnvironPowerPt/EnvironPowerPts/Agriculture%5B1%5D.ppt