Soil and the Soil Ecosystem

1. Soil and the Soil Ecosystem 1

2. Why Study Dirt? • 90% of the world’s food comes from land based agriculture • 22% of the land used for crops, grazing, and forestry has become degraded during the past fifty years (See Table 8-1 p.187). 2

3. http://www.globalchange.umich.edu/globalchange2/current/lectures/land_deg/concern.gifhttp://www.globalchange.umich.edu/globalchange2/current/lectures/land_deg/concern.gif 3

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6. Areas of the planet threatened by soil erosion 6

7. Loss of Farmland to Development is Something We Experience Locally 7

8. No healthy topsoil = No us. 8

9. What is Healthy Soil? Add to this air, water, soil nutrients, salts, and pH. 9

10. Soil Formation—Mineral Soil • Soil building begins with the physical and chemical fragmentation of the Parent Material. • Mechanical Weathering • Temperature change • Abrasion • Chemical Weathering • Acid deposition • Oxidation • Type of parent material and the climate determine the type of mineral soil. 10

11. Soil Formation—Detritus • Detritus is Decaying plants and animals. • Supplies nutrients for plants • Lowers soil pH • Makes inorganic nutrients available to plants by increasing their solubility • Typical range pH 6-8. 6-6.5 optimum for biological activity in most soil ecosystems. • Creates a loose texture that increases aeration and water infiltration / water holding capacity. 11

12. Soil Formation—Detritus • Optimum organic matter content for most non-wetland soil ecosystems is 3-5% • Detritus that has undergone most of its decomp. Is referred to as humus • humus-detritus that has been almost completely digested by the detritus feeder food web. • humus will decomp @ 2%-5% of vol./yr. 12

13. Soil Formation—Detritus Food Web • Microflora (the decomposers) help to unlock the nutrients stored in detritus and make them available to the rest of the DFW. • Burrowing animals aerate the soil and mix the organic and inorganic components of the soil. • 1 ha of healthy soil may contain 500k earthworms that can process 9 metric tons (20 k lbs) of soil/year. • See handout for other denizens of the soil 13

14. Bacteria are the most important organisms in the detritus food web. They are the first heterotrophs in any food chain. • 15 tons/ acre 14

15. Rate of Topsoil Formation • Varies depending on the conditions of the area, but primary sources list a range from 1” every 50 to 500 years. • That’s a long time to wait for a meal. 15

16. Soil Characteristics • Soils differ greatly from one area to another. • Even on relatively small plots of land, soil types may differ. • Soils are generally studied according to their • Profile • Texture • Structure • Color 16

17. Soil Profile page188 17

18. SoilTexture Page189 18

19. Soil Texture • Sand are the largest particles and they feel "gritty." • Silt are medium sized, and they feel soft, silky or "floury." • Clay are the smallest sized particles, and they feel "sticky" and they are hard to squeeze. 19

20. Loam is common and generally considered ideal for plant growth. • Properties of Soil Particles Worth Noting: • large particles have large spaces separating them • small particles have a larger surface area to volume ratio • Nutrient ions and water molecules cling to surfaces • Workability (Tilth)-the ease with which a soil can be cultivated 20

21. Soil Consistence • Loose • Friable • Firm • Extremely Firm • Source 21

22. Soil Structure 22

23. Soil Structure 23

24. Soil Structure • Soil Structure-the “feel” of the soil (clumpy, soft, loose, etc.) • Soil Structure vs. Soil Texture 24

25. Soil Color • Quantified by horizon and inclusions using the Munsell Soil Color Charts. 25

26. Soil Color 26

27. Soil and Plants • Plant considerations pertaining to soil: • nutrients • water • air • pH • salinity • These factors together affect the fertility “tilth” of the soil. 27

28. Nutrients • Nitrogen (N2, NO3-, NO2-, NH3) • Phosphate (PO43- ) • Potassium (K+)  • Calcium (Ca2+) • These are added to the soil by weathering of parent material, fixation by bacteria from the atmosphere, and through decomposition of detritus. 28

29. Nitrogen • Needed for chlorophyll synthesis. • Leafy growth above ground. • Hasten maturity of crops. • Enhance fruit development. • Optimum amounts present in soil depend 29

30. Phosphorus • Encourages cell division • Encourages root development • 50 – 75 lbs / acre typically available to plants for growth. 30

31. Potassium • Enhances disease resistance • Activates enzymes needed for development • Cuticle development • Regulates turgor pressure • Necessary for protein metabolism 31

32. Other Soil Properties • leaching • nutrient-holding capacity • ion-exchange capacity • Organic vs. Inorganic Fertilizer 32

33. Water • Infiltration • What it is • Why it matters • How to measure it • Water Content • What it is • Why it matters • How to measure it 33

34. Water • Water Holding Capacity • What it is • Why it matters • How to measure it • Evaporative Water Loss • What it is • Why it matters • How to measure it 34

35. Air • the ability of the underground organs of plants to exchange gases with the outside environment is essential for their survival. Roots need air to grow. • Many things affect the aeration of soil. • mineral particles • OMC • Actions of Detritus Feeders and other animals • Actions of plants • Weather 35

36. pH • from water • from detritus • from mineral soil • evaporative qualities 36

37. Salinity • Plants must maintain an osmotic balance with their external environment. • addition of salt to the soil prevents plants from taking up water into their roots 37

38. Soil As an Ecosystem Nebel p.192 38

39. There is an 85% to 95% decline in GPP when plants are grown on subsoil compared to when they are grown on topsoil. • Loss of humus in topsoil is called mineralization 39

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