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What Makes Plants Thrive?


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Erin Silva from the UW-Madison agronomy department discusses what you need to do to help your plants flourish.

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What Makes Plants Thrive?

  1. 1. What Makes Plants Thrive?Photo credit:
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  3. 3. How To Ask QuestionsClick on the word bubble in your webinar window toask a question.For technical assistance during the presentation, call1-800-442-4614Click on the word bubble in your webinar window toask a question.For technical assistance during the presentation, call1-800-442-4614
  4. 4. “What Makes Plants Thrive?” Why start the discussion with soil?
  5. 5. Organic Agriculture (USDA NationalOrganic Program) Recognition that healthy soils are thefoundation of sound, sustainable agriculturesystem primary focus of organic farming is to usepractices that build healthy soils
  6. 6. National Organic ProgramSection 205.203(a) Select and implement tillage and cultivationpractices that maintain or improve thephysical, chemical, and biological condition ofsoil and minimize soil erosion
  7. 7. Soils: More Than “Just Dirt” Aim of organic and sustainable farming: toimprove the soil Encourage soil organisms Supply nutrients in sufficient quantity withoutoversupplying Maintain tilth and minimize compaction Build organic matter
  8. 8. Outline for today What is soil? Soil textures Soil organic matter Soil fertility management in relation to abovefactors
  9. 9. What is a soil? Characteristics of an ideal soil Components of a soil Appearance of a soil Soil texture/ soil type
  10. 10. Characteristics of an ideal soil What are characteristics of ideal soils? Fertile Deep Well drained/ aerated High in organic matter Friable soil is easily worked
  11. 11. Components of SoilMineralOrganicWaterAir
  12. 12. Soil Air Oxygen supports soil life Roots Microbes Air can be displaced by water
  13. 13. Management Question: The management of what important factor torelated to plant growth must be considered inrelationship to soil air?
  14. 14. Irrigation! Saturated soils – over-irrigation, poor drainage Water fills in all the air spaces – no room left for air Affects root growth/health, soil biological activity,available nitrogen
  15. 15. Mineral and organic components A substance with a complex structureconsisting of: Broken down rock particles (mineral component) Organic matter Ideal soil is about 5-6% Function of organic matter Source of food for soil microorganisms Source of nutrients for plants Holds minerals against loss from soil due to leaching Holds water where plants can access it
  16. 16. Soil Profile Topsoil It is the darkest layer of thesoil because it containsorganic matter and humus. Contains majority of feedingroots of plants Subsoil Low in nutrients Contains fewmicroorganisms Structure of subsoil isimportant for drainage
  17. 17. Example of asoil profile• Note the darkorganic horizon atthe surface andchanges in colorand structure downthe profile
  18. 18. Soil texture Determined by mineral component Coarseness or fineness of soil
  19. 19. Soil texture Clay Soil particles are less than0.002 mm in size Does not drain easily and isdifficult to work Root growth is poor due tosmall spaces between soilparticles
  20. 20. Soil texture Silt Particle size is between0.002 to 0.05 mm Feels silky to the touch
  21. 21. Soil texture Sand Sand particles range insize from 0.2 mm forthe very finest sand to 2mm for the coarsest Feels gritty if rubbedbetween your fingers Warms up and driesearly in spring Low in nutrients
  22. 22. Soil Types Most soils are a mixture of different soil textures Often a soil type will be dominated by a particular texture Can group soil types by how well they drain and majortexture class they contain Heavy soils Contain a high proportion of clay Light soils Contain a high proportion of sand Important to know the soil type because it will determine themanagement practices you need to use
  23. 23. Why is soil texture important? The texture will determine how much air is insoil and how well water flows through the soil Determines how easily the soil is worked
  24. 24. How might you manage a clay soil different than asandy soil? Irrigation – sandy soils will hold less water Types of crops – some crops do better in alighter soil (root crops, squashes) Fertility – may need to do in-seasonapplications in sandy soil Cultivation/cover cropping – Beware of erosion!
  25. 25. Pause for Questions....
  26. 26. Soil Organic Matter Many soil properties impact soil quality, butorganic matter deserves special attention Affects several critical soil functions, can be manipulatedby land management practices, and is important in mostagricultural settings across the country Because organic matter enhances water and nutrientholding capacity and improves soil structure, managingfor soil carbon can enhance productivity andenvironmental quality, and can reduce the severity andcosts of natural phenomena, such as drought, flood, anddisease
  27. 27. Soil Organic Matter Living Roots Earthworms and insects Microorganisms Dead Fresh plant residues Releases nutrients as it decomposes – allows for slow, steady release Recently deceased soil organisms Active organic matter Very Dead Well decomposed organic materials Humus Slow to decompose – may last 100’s of years Hay, cornstalks Not well understood
  28. 28. Characterization of Organic Matter:Humus
  29. 29. Organic Matter Generally 0-6% Reservoir for nutrients, improves soilaeration, drainage, water holding capacity Very complex compounds Difficult to characterize chemically Biologically controlled Very dynamic- differs depending on moisture,temperature
  30. 30. Humus Very well decomposedorganic matter refers to any organic matter that has reached a point ofstability, where it will break down no further andmight, if conditions do not change, remain as it is forcenturies, if not millennia Mineralization of organic matter to soil humusreleases some amounts of nitrogen, phosphorousand sulfur from organic forms, and candramatically influence the availability ofmicronutrients
  31. 31. Relative amounts of OM throughout US
  32. 32. Pause for Questions...
  33. 33. 16 essential elements: C, H, and O: not consider minerals Macronutrients: Primary macronutrients: N, P, and KNeeded in relatively large amounts Secondary macronutrients: Ca, Mg, S Micronutrients: Cl, Fe, B, Mn, Zn, Cu, Mo Required in small amounts Supplied through: Compost, cover cropping, fertilizers (both organic andsynthetic) If any one is missing or low, plant productivity islimited
  34. 34. How do plants take up nutrients? By roots Must be plant available
  35. 35. Soil solution and nutrient uptake
  36. 36. Ions Cation Calcium, magnesium Anion Certain forms of nitrogen
  37. 37. Nutrients in Ionic phase Magnets: opposites attract
  38. 38. Molecules: opposites also attract
  39. 39. Soil acts as a magnet Attracts and retains positively charged ions insoil solution Prevents them from moving downward withwater
  40. 40. Clay and Cation Exchange CapacityBrady & Weil, 2004. Elements of the Nature and Properties of Soils
  41. 41. Cation Exchange Capacity (CEC) It is the ability of clay, organic matter, and humus toattract positive ions Clay, organic matter, and humus all have negative chargeson their surfaces Most nutrients (P, K, Ca, etc) are cations or have positivecharges “Opposites attract” The higher the cation exchange capacity, the moreclosely the nutrients are held and the less likely theyare to be lost to leaching
  42. 42. Soils with high CEC Hold more nutrients Avoid rapid changes in levels of nutrients insoil solution
  43. 43. High vs. Low CEC
  44. 44. Soil organic matter and CEC Structure of soil organic matter is extremelycomplex, with that can interact with cations (plantrequired nutrients) Often contributes from 30 to 90% of the total chargepresent in the soil surface, even when present inrelatively low amounts.
  45. 45. pH Dependent Charge on OM
  46. 46. What else has positive charge andaffected by CEC? Water
  47. 47. OM vs. Clay Because of it complex and open structure, theability of humus to pull water from thesurrounding saturated atmosphere of the soilsapproaches 80 to 90% of its weight, ascompared to 15 or 20% for soil clays. Humus does not readily fix exchangeablecations, as do some clays, but maintains theseions in an easily exchangeable form
  48. 48. Management High CEC soils (high clay content, moderate tohigh organic matter content) high water holding capacity – be careful not to over-irrigate low leaching potential for cationic nutrients - lessfrequent need for lime and fertilizers (except N) their physical properties may make it difficult for afarmer to cultivate or maintain good aeration
  49. 49. Management Low CEC soils (high sand, low organicmatter) need for more frequent irrigation may need to apply fertilizer throughout season tomeet plant demand may be more prone to erosion can be easier to work
  50. 50. Questions?