SOIL PROPERTIES A crash course in soils

1. SOIL PROPERTIESA crash course in soils D. Smith Raleigh Charter H.S. 2005-06

2. What is Soil?? • Soil is the top layer of the Earth’s surface. • 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 • Mineral matter comes from parent material • Air & Water percents are interchangeable • Humus is organic matter! Water (~25%) Humus (~5%) Air (~25%) Mineral (~45%)

4. Why are soils important? Soils are important: • As a habitat for growing crops • Food • Fabrics/Dyes • Rubber/Building Materials • 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 • Medium for photosynthesis

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

6. Soil Composition continued… • Mineral Matter • Provides nutrient minerals for plants • Provides pore space for water & air • Older soils are: • More weathered • Lower in certain essential nutrient minerals • Humus: black/dark brown organic material remaining after decomposition • Leaf litter, animal dung, & decaying organisms • Increases the soil’s water-holding capacity by acting like a sponge

7. 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

8. Physical Weathering • Followed by Erosion (Wind, Water, Ice) • What are “agents” of physical weathering? • Tree roots/plant roots • Frost wedging: • Water collects in cracks in rock • Water expands when it freezes • Pieces of rock break off

9. 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

10. Chemical Weathering • Most chemical weathering involves gases in the atmosphere (oxygen and carbon dioxide) and/or water • Example: Think about metal rusting • You go from metal to rust—a chemical reaction has taken place

11. Topsoil Formation

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

13. Earthworms & Ants: • Cycle minerals • Aerate the soil • Decomposing corpses contribute organic matter • Assist plants in reproduction by burying seeds • Mycorrhizae • Symbiotic relationship between fungi and the roots of vascular plants • Fungus absorbs nutrients from the soil, and provides it for the plant. • Plant produces food (photosynthesis), and provides it for the fungus.

14. Soil Food Web

15. Soil Food Web (incl. humans)

16. Dr. Greg Pillar, Queens College

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

18. SOIL TEXTURE • Soil texture: The way a soil "feels" • Depends on the fraction 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.

19. Physical Property: Texture • Texture is determined by its % sand, silt, and clay. • Texture determines the type of soil, and the soil’s properties. Loam: ideal for agricultural soil

20. Why care about soil texture? • Predicts soil properties-fertility, etc. • Sandy soils • low organic matter • Poor retention water and nutrients (it flows through) • As silt and clay fractions increase, soils • 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 and are called LOAM

21. Check-In

22. Physical: Porosity & Permeabilityagain… Think it is important?? • Definition? • amt of soil pore spaces (aeration) Porosity Permeability • Definition? • ability of water to percolate through • ____ porosity = ____ permeability

23. Soil Composition continued… • As water infiltrates the soil, it can carry dissolved materials with it. • Leaching: Removal of dissolved materials from the soil by water percolating downward • Illuviation: Deposition of leached material in lower layers • Some substances completely leach out of the soil because they’re so soluble that they migrate right down to the groundwater.

24. Physical: Ionic Charge • Soil minerals are often present as ions. • Minerals ions are either positively or negatively charged. • Clay particles have mostly negative charges on their outer surfaces. • Positively charged mineral ions are attracted to the soil particles and are held for plant use. • potassium K+ and magnesium Mg2+ • Negatively charged mineral ions are repelled by the soil particles and are washed away from roots. • nitrate NO3-

25. Physical Characteristics (review) • Why would 100% sand be undesirable for plants? • Why would 100% clay be undesirable for plants? • Answer SAND / SILT / CLAY for the following: • A soil with a lot of _____ would have good drainage, but poor nutrient-holding characteristics. • A soil with a lot of _____ would have poor drainage, but good nutrient-holding characteristics. • A soil with a lot of _____ would have low porosity. • A soil with a lot of _____ would have high permeability.

26. Chemical Property: pH • Most soil pH is 4-8. Plants are happiest at 6-7.  • Plants are affected by soil pH. (1) The solubility of certain nutrient minerals varies with differences in pH • Low pH = Al & Mn are more soluble, and can be absorbed in toxic amounts. • High pH = some salts are less soluble, and are less available to the plants. (2) Soil pH affects the leaching of nutrient minerals. • Acidic soil = positively charged ions are less soluble and are unavailable for 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

27. Plant pH Preferences

28. Soil Conditioners (Lime) • CaCO3 or MgCO3 • Soil amendment / conditioner… not a fertilizer! • Important functions: • Corrects soil acidity • Adds important plant nutrients— Ca & Mg • Reduces solubility & toxicity of certain elements in the soil • Al, Mn, Fe • This toxicity could reduce plant growth under acid conditions. • Promotes availability of major plant nutrients. • Zn, Cu, P • Increases bacterial activity & mutualistic relationships. http://www.wvu.edu/~Agexten/hortcult/turf/liming.htm

29. Soil stores important nutrients Phosphorus (P) Nitrogen (N) Potassium (K) Calcium (Ca) Magnesium (Mg) Dr. Greg Pillar, Queens College http://www.lesco.com/

30. Soil Nutrients • Nitrogen • Phosphorus • 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

31. NITROGEN FUNCTIONS • Used to make chlorophyll • Responsible for rapid growth and health green leaves TOO LITTLE/TOO MUCH • Not enough nitrogen?  Plant leaves turn yellow • Too much nitrogen?  Long weak stems/no flowering MOVEMENT THROUGH and TO THE SOIL: • Nitrogen Cycle 

32. PHOSPHORUS FUNCTION • Responsible for root development and growth • Helps plant produce flowers and fruit • Important in photosynthesis and respiration, energy transfer and storage TOO MUCH/TOO LITTLE • Not enough phosphorus?  Purplish or deep green leaves  Poor root system • Too much phosphorus?  No symptoms  Plants NEVER have too much phosphorus—there’s not a lot out there—what does exist bonds to soil or leaches away quickly MOVEMENT THROUGH and TO THE SOIL: • Phosphorus cycle

33. What is a soil profile?

34. Hey, look at all the layers! That’s the soil profile… Picturing a Soil Profile Imagine a hill… Layers are called horizons Imagine the bulldozer taking a good chunk out of that hill. Imagine a bulldozer…

35. 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- eluvial, mineral horizons which lie at or near the surface and are characterized as zones of maximum leaching (E = Exit) 􀂄B- illuvial, washed in, layer of accumulation (I = Into) 􀂄C- unconsolidated material under A&B layers 􀂄 Bedrock

36. Soil profile example Maryland Soil Profile

37. Soil Profile Example 2 Florida Soil Profile

38. Some Review Questions • What effect does temperature have on soil? • It controls how fast organic material breaks down • How might pH affect soil? • It changes what nutrients are available and toxins (e.g. metals) in the soil • What is a soil profile? • The cross-section of soil that shows different layers