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  1. SOIL

  2. Soil50% pores and 50% solids

  3. SandA soil solid • No electrical charge • Very large pore spaces • Water drains rapidly

  4. ClayA soil solid • Retains nutritional elements (due to negative electrical charge) • Very small pore spaces • Water drains very slowly

  5. (A cation is an atom with a positive charge) Represent the negative charge on clay particles. An individual clay particle cannot be seen by the unaided eye. It is less than two thousandth of a millimeter (0.002 mm). 20 MILLION hydrogen atoms laid in a line would equal 1 mm

  6. Most of the nutrients that plants need have a positive electrical charge. Primary nutrients • N+/- • P+ • K+ • S- • Ca+ • Mg+ • Fe+ • Mn+ • Cu+ • Zn+ • B+ • Mo- • Al+ Secondary nutrients Micronutrients {Ni+ and Cl- are sometimes included}

  7. Soil can be thought of as a storehouse for plant nutrients.

  8. SOIL Soil provides all that a plant needs with the exception of…

  9. SOIL CO2 sunlight

  10. soil does provide: • Oxygen • Water • Nutrients (13-14)(N,P,K,S,Ca,Mg,Fe,Mn,Cu,Zn,B,Mo,--Al,Cl,Ni) • Some sources include aluminum (Al) while others list chlorine (Cl) and nickel (Ni) as micronutrients

  11. Tilth Suitability of a soil to support plant growth {physical condition of a soil}

  12. Tilth Relates to: • Structure • Aggregate formation – greater degree of aggregation = better tilth • Texture is the percent of: • Clay, Silt and Sand minerals

  13. Aggregates--soil structure-- • Soil particles that are held together by • Sticky organic substances produced by microorganisms and plant roots. (polysaccharides – i.e. sugars) • Enmeshment – fungal hyphae and fine plant roots • Electrostatic forces

  14. Tilling • Cultivation: • Breaks apart aggregates • Collapses pores • AVOID TILLING EXCEPT TO: • Mix in organic matter • Control weeds • Prepare seed beds

  15. Better tilth means better access to the essentials for growth • Oxygen • Water • Nutrients (13-14)(N,P,K,S,Ca,Mg,Fe,Mn,Cu,Zn,B,Mo,--Al,Cl,Ni)

  16. Tilth Suitability of a soil to support plant growth (physical condition of a soil); -moisture retention -drainage -aeration -ease of seed germination and emergence -ease of root development & penetration -ease of tillage -does not directly pertain to nutrition

  17. relative Size of Sand, Silt and Clay Clay below 0.002 mm - sticky Silt 0.002 to 0.05 mm - silky Sand 0.05 to 2.0 mm - gritty

  18. The diameter of a clay particle is 1,000 times smaller than the diameter of a large grain of sand or the thickness of a key (the average house key is 2 mm thick). Individual clay particles can only be seen with a microscope.

  19. Relative size of soil particles

  20. Small Pores in clay can prevent plants from getting water ≈capillary action ≈ • In low water conditions, the clay will feel moist but the water is not available for the plants. • Under these low water conditions, capillary action results in water being held so tightly to the clay particles that the forces of transpiration cannot overcome the adhesive forces holding the water to the clay.

  21. Transpiration • Transpiration is the evaporation of water from plants. It occurs chiefly at the leaves while their stomata are open. • Transpiration is the "engine" that pulls water up from the roots to: • supply photosynthesis; • bring minerals from the roots for biosynthesis within the leaf; • cool the leaf.

  22. Moist Clay ≠ Happy Plants • When there is minimal water present, it will only fill the very small areas between the clay particles. • Under these conditions, the force of attraction between the soil and water is greater than the forces exerted by transpiration to pull the water into the roots. • The net result is that the clay feels and looks moist but the water is bound too tightly to be available to the plants.

  23. Roots can get water as long as they can overcome the adhesive forces that hold water to the soil particles.

  24. Soil pores… …are multi-access highways for: - air - water - soluble nutrients - plant roots - microbes

  25. Medium sand silt Comparing pore spaces in sand to those in silt.

  26. Medium sand silt Pores enable: -aeration-moisture availability -root growth -

  27. Adequate Oxygen levelsand soil tilth • Plenty of pores for optimum oxygen diffusion • Good drainage to avoid water saturation

  28. Healthy white roots

  29. -- low soil oxygen is the most common limiting factor of plant (root) growth. ~small pores and/or excessive water~

  30. Oxygen is necessary for the normal growth processes of root and plant • Oxygen diffuses through air in soil pores • Oxygen diffuses very slowly through water • Oxygen dissolved in water is used up very quickly and new oxygen arrives very slowly by diffusion.

  31. Root development in self-watering containers Poorly developed roots due to excessive water. Notice the lack of healthy, white roots. Healthy roots in container with adequate water supply.


  33. Loam≈ A type of soil that does not include any organic material!

  34. Loam consists ONLY of minerals (sand, silt and clay)

  35. Sandy loam ≈≈≈ Good soil for a garden is SANDY LOAM TRUE LOAM has too much silt and clay to drain readily and is a poor soil for garden use.

  36. Sandy Loam Good soil for a garden is SANDY LOAM -less silt and clay and more sand than a true loam -sand should be predominately coarse and medium sized particles (i.e. >0.25mm)

  37. Clay soils are usually: • Fertile - negative charge so good nutrient retention (storehouse) • Tend to compact and thus limit O2 availability • Inadequate pore space for good air and water movement • As little as 20% clay particles result in soil behaving like a clayey, sticky soil. Source: Colorado State Extension Service

  38. Soil Texture Triangle

  39. AMENDMENTS • IMPROVING SOIL TILTH • Water retention --addition of organic material -addition of vermiculite (not perlite) -addition of clay to sandy soil -what about underlying clay soil?(it will limit drainage) • Pore size • Nutrient retention

  40. AMENDMENTS • VERMICULITE • Increases moisture holding capacity • Increases pore space • PERLITE • Low water holding capacity • Increases pore space

  41. Tilth Suitability of a soil to support plant growth (physical condition of a soil); -moisture retention -drainage -aeration -ease of seed germination and emergence -ease of root development & penetration -ease of tillage

  42. AMENDMENTS • IMPROVING SOIL TILTH • PROVIDING NUTRIENTS • Microbial activity (see SOIL {2}) • Correcting deficiencies • Soil test (LSU – pH, P, K, Ca, Mg, Na, S, Cu and Zn)