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SOILS ANDPOTTING MIXESGreen Industry TrainingSpring 2013Dr. Heidi Kratsch
Outline•Soil texture, structure, chemical properties•Topsoil qualities•Organic matter•Potting media•Ingredients•Proportion...
Plant roots need gases• Oxygen - burns (respires) sugars provided by the  canopy (leaves) for energy• Release carbon dioxi...
Composition of a typical soil                  Water      Mineral      fraction                    Air            Organic ...
Soil texture      The      mineral      particles:      sand, silt,      and clay
The effect of particle size   Sand particles     Clay particles           Air flow  Water flow
Texture effects on soil physical propertiesTexture     Available water   Aeration   Drainage CompactionSandLoamSilt loamCl...
Soil texture and drainage  Coarse      Medium             Fine  Texture     Texture           Texture            Silt Loam...
Answer: No…!•Why? It’s a problem of scale: • Soil weighs about 90 lbs per cu. ft. • Soil from a hole 3 ft. in diameter by ...
WHAT CAN I DO?Answer: Enhance soilSTRUCTURE
Soil structure • The combination of sand, silt and clay (with   organic matter) into secondary particles called   aggregat...
Structure develops over time
Compaction•Destroys soil structure•Seals off soil surface•Stress – perhaps death of plants
Impact is worse when soil is wet
Effect of compaction on plants
Soil layers (horizons)                •In an undisturbed                 setting, soils are                 allowed to for...
The reality in urban areas….
Excavation and Fill Soils•Needed to provide proper grade and surface drainage, but…•Generally low in organic matter • Exca...
Effect of construction on soil drainage
Excessive drainage problem•Very sandy soil•Coarse soils are naturally droughty within hours after rain•Add extra organic m...
Amending soils with organic matter• Improves drainage and aeration of clay soils• Improves water-holding capacity of sandy...
Water and Mineral Nutrients
Water and mineral nutrition• Water action helps release minerals into the soil  solution (dissolving, freeze-thaw breakdow...
Soil chemical properties greatly affect therelease of nutrients or the movement of water• Soil texture• pH affects mineral...
What is pH?• pH is measured as the ―activity‖ or concentration of  hydrogen ions (H+) in the solution.• The higher the con...
• Why worry about soil pH?• Affects the dissolution of  soil minerals• Generally, higher pH =  lower mineral availability
CAN’T I JUSTACIDIFYMY SOIL?
Answer: No• Why? Another problem of scale:• Western soils have VERY large reservoirs of pH  buffers in the soil (solid car...
Buffering reactions:   CaCO3 + CO2 (in water)  Ca2+ + 2 HCO3(Calcium Carbonate)                (Bicarbonate)   HCO3 + H+ ...
Major pH-related problem: iron chlorosis
pH tolerant = iron-efficient plantsIron-inefficient   Intermediate     Iron-efficientQuaking aspen      Red maple        A...
SOIL SALINITY
Soil salinity = soluble salts in soil• Salts inhibit plant growth through ―chemical  drought‖ (induced water stress), spec...
Salinity and plant adaptation                           Soil EC (dS/m) 0        2         4        6         8        10  ...
Sources of salts• Natural deposits• Residual salts in new development areas (watch  fill soils)• Irrigation waters • natur...
Other salt problems• Sodium saturated, or Sodic soils can become  dispersed (involves clay particles).  • Breaks down soil...
Flocculated, aggregated clay    Dispersed, crusted clay
Boron• Essential mineral (specific ion) – becomes toxic  above 0.5-1.0 ppm• Occurs in arid, young soils• Other sources: we...
Boron toxicity symptoms in bur oak
Leaching salts with water• Ensure that soil has good internal drainage.  Water must move through the soil to carry salts  ...
Do amendments help?• Gypsum (calcium sulfate) • Used along with leaching • only effective for sodic soils• Sulfur • May be...
Step Back – Big Picture Review
―Typical‖ Nevada soils• Arid/Droughty conditions  • Low precipitation  • Coarse, sandy soils• High pH (alkaline – 7 to 8+)...
IF I CAN’T FIX THE SOIL, WHAT DO I DO?• Choose species adapted  to the conditions at hand• Prepare soils for best  possibl...
Potting mixes1. Anchorage and   stability2. Water3. Nutrients4. Aeration
Possible components• Field soil• Sand• Calcined clay• Perlite• Polystyrene• Peat moss• Pine bark• Hardwood bark• Coconut f...
Why not field soil alone?1. Anchorage and stability2. Water3. Nutrients4. Aeration
Pots restrict how water drains              Gravity
Shift towards soilless potting mixes•Do not need to be pasteurized (sterilized)•Lighter in weight (lower shipping costs)•M...
Properties of soilless potting mixes •Water retention •Aeration •DrainageThe goal is to increase aeration without decreasi...
Coarse mineral components•Perlite •   Volcanic origin •   Low bulk density •   Good drainage and aeration •   Low CEC and ...
Sand• Coarse concrete-grade  (washed)• High bulk density• Excellent drainage and  aeration• Increases water-holding  when ...
Calcined Clays • Good water- and nutrient-holding capacity • Excellent drainage qualities • Provides Coarse Texture and Ag...
Bulk Density•How heavy per unit                        Bulk density at                                                 CC ...
PeatsLess decomposed   • Sphagnum moss - a moss that grows in                   acid bogs in North America, Canada, and   ...
Sphagnum moss                      Sphagnum moss peat – pH 3.0 to 4.0                                   Hypnum moss peat– ...
Peat-based mixes•Common formulations: • Sphagnum peat moss / vermiculite (1 : 1) • Sphagnum peat moss / perlite (1 : 1)•Ex...
Coir (coconut) fiber – alternative to peat?• Made from coconut  husks.• High water-holding  capacity• Excellent drainage• ...
Bark-based products                              • Cheaper than                                Sphagnum peat              ...
Pasteurization• Eliminates disease  organisms, insects,  nematodes, weeds.• Steam: 160F for 30 min• Soil-based substrates ...
Other Pre-plant Additives• Dolomitic limestone • Correct the pH or acidity of a   mix• Phosphate • Superphosphate (0-45-0)...
Organic mixes• OMRI – • Organic Materials Review   Institute • Assures products are   consistent with the   requirements o...
Compost and manure                                 rules:Compost                          1. Pile must be 131-170F for• Ra...
Summary – container substrates• Stable product that will not shrink in volume during  plant production / shelf time.• Bulk...
Questions?             Contact:          Heidi KratschUniversity of Nevada Cooperative            Extension     Phone: 775...
2013 Green Industry Training: Soils and Potting Mixes
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2013 Green Industry Training: Soils and Potting Mixes

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2013 Green Industry Training: Soils and Potting Mixes

  1. 1. SOILS ANDPOTTING MIXESGreen Industry TrainingSpring 2013Dr. Heidi Kratsch
  2. 2. Outline•Soil texture, structure, chemical properties•Topsoil qualities•Organic matter•Potting media•Ingredients•Proportions•Selection
  3. 3. Plant roots need gases• Oxygen - burns (respires) sugars provided by the canopy (leaves) for energy• Release carbon dioxide in the process• If the two gases cannot freely exchange with the atmosphere • respiration shuts down • roots die off • Plants can’t get water or nutrients.• Many root- and wood-rotting organisms (fungi) thrive in low oxygen soil conditions.
  4. 4. Composition of a typical soil Water Mineral fraction Air Organic matter
  5. 5. Soil texture The mineral particles: sand, silt, and clay
  6. 6. The effect of particle size Sand particles Clay particles Air flow Water flow
  7. 7. Texture effects on soil physical propertiesTexture Available water Aeration Drainage CompactionSandLoamSilt loamClay loamClay
  8. 8. Soil texture and drainage Coarse Medium Fine Texture Texture Texture Silt Loam Clay Loam Sand Can’t I just add Sand or Clay to balance the condition of the soil?
  9. 9. Answer: No…!•Why? It’s a problem of scale: • Soil weighs about 90 lbs per cu. ft. • Soil from a hole 3 ft. in diameter by 2 ft deep is about 18 cu. ft., and weighs 1600 lbs. • To change the texture by 10 to 20% would require 160 to 320 lbs of material (sand or clay) • Requires considerable expense and effort • Could just be creating cement!
  10. 10. WHAT CAN I DO?Answer: Enhance soilSTRUCTURE
  11. 11. Soil structure • The combination of sand, silt and clay (with organic matter) into secondary particles called aggregates Soil aggregate
  12. 12. Structure develops over time
  13. 13. Compaction•Destroys soil structure•Seals off soil surface•Stress – perhaps death of plants
  14. 14. Impact is worse when soil is wet
  15. 15. Effect of compaction on plants
  16. 16. Soil layers (horizons) •In an undisturbed setting, soils are allowed to form naturally. •Over time, provides ideal conditions for plant roots.
  17. 17. The reality in urban areas….
  18. 18. Excavation and Fill Soils•Needed to provide proper grade and surface drainage, but…•Generally low in organic matter • Excavated subsoils (basement, grade cut…) • Often stockpiled for extended periods (much of the organic matter decomposed in 2 to 6 months)•Thoroughly disturbed, mixed and broken up, structure has been reduced, even eliminated.
  19. 19. Effect of construction on soil drainage
  20. 20. Excessive drainage problem•Very sandy soil•Coarse soils are naturally droughty within hours after rain•Add extra organic matter (for retention)•Precise water management (frequent, low volume – like drip/trickle systems)
  21. 21. Amending soils with organic matter• Improves drainage and aeration of clay soils• Improves water-holding capacity of sandy soils• Reduces compaction• Provides/retains nutrients• Locally lowers soil pH• NOTE: Add no more than 25% by volume • Higher levels can cause significant soil settling as OM breaks down
  22. 22. Water and Mineral Nutrients
  23. 23. Water and mineral nutrition• Water action helps release minerals into the soil solution (dissolving, freeze-thaw breakdown— weathering of rock)• Water is the medium by which mineral nutrients travel to, into, and through the roots
  24. 24. Soil chemical properties greatly affect therelease of nutrients or the movement of water• Soil texture• pH affects mineral form and release• Accumulation of salts: carbonates, sodium, chloride and sulfates, etc.) can restrict water and nutrient uptake, or alter soil structure
  25. 25. What is pH?• pH is measured as the ―activity‖ or concentration of hydrogen ions (H+) in the solution.• The higher the concentration of hydrogen ions, the lower the pH (more acidic). 2 4 6 8 10 12 acidic Neutral alkaline (7.0)
  26. 26. • Why worry about soil pH?• Affects the dissolution of soil minerals• Generally, higher pH = lower mineral availability
  27. 27. CAN’T I JUSTACIDIFYMY SOIL?
  28. 28. Answer: No• Why? Another problem of scale:• Western soils have VERY large reservoirs of pH buffers in the soil (solid carbonates and other minerals, ex. ―free lime‖) • 1% CaCO3 in an acre-foot of soil weighs 40,000 lbs • Nevada soils frequently contain 20-30%• All buffering compounds would have to be dissolved and neutralized before the pH will drop.
  29. 29. Buffering reactions: CaCO3 + CO2 (in water)  Ca2+ + 2 HCO3(Calcium Carbonate) (Bicarbonate) HCO3 + H+ (in water)  CO2 + H2O (this is just one acid neutralization reaction -- no change in pH, i.e., no increase in free H+)Added acid (H+) is consumed until all Carbonates are dissolved, or other cations leached from the system (i.e., Total Alkalinity is neutralized).
  30. 30. Major pH-related problem: iron chlorosis
  31. 31. pH tolerant = iron-efficient plantsIron-inefficient Intermediate Iron-efficientQuaking aspen Red maple AshSugar maple European beech LindenSweetgum Horsechestnut Scotch pineSilver maple Baldcypress GinkgoPin oak Quaking aspen Burr oak
  32. 32. SOIL SALINITY
  33. 33. Soil salinity = soluble salts in soil• Salts inhibit plant growth through ―chemical drought‖ (induced water stress), specific ion toxicity, or soil dispersion (Sodium salts)• Visual diagnosis: salt crusting/salt burn• Electrical conductivity (EC) is the measure of soil salinity. • EC > 2 deciSiemens/meter can harm plants• SAR – Sodium Adsorption Ratio • SAR > 13 is sodic, but soil problems can occur at lower levels.
  34. 34. Salinity and plant adaptation Soil EC (dS/m) 0 2 4 6 8 10 12 14 16 Berries Apple Alfalfa---| Corn----| Spinach----------| Bluegrass Tall fescue-------------| Alder-----------| Cottonwood----| Barley----------------------------------------------| Wheatgrass-----------------------------------------------|
  35. 35. Sources of salts• Natural deposits• Residual salts in new development areas (watch fill soils)• Irrigation waters • natural sources (esp. shallow wells) • water softeners (high in sodium)• Deicing salts (road throw and sidewalk runoff)• Over-application of fertilizers or manure and compost
  36. 36. Other salt problems• Sodium saturated, or Sodic soils can become dispersed (involves clay particles). • Breaks down soil structure • Seals soils to air and water penetration• Specific toxicities to specific salt constituents
  37. 37. Flocculated, aggregated clay Dispersed, crusted clay
  38. 38. Boron• Essential mineral (specific ion) – becomes toxic above 0.5-1.0 ppm• Occurs in arid, young soils• Other sources: well water, reclaimed water, geothermal springs, earthquake faults• Mobile in soils – moves up with moisture evaporation from soil• Boron-laden soils are often salty too!
  39. 39. Boron toxicity symptoms in bur oak
  40. 40. Leaching salts with water• Ensure that soil has good internal drainage. Water must move through the soil to carry salts out • Add organic matter • Deep tillage/ripping (not near established trees)• Apply water over 1-2 days • 6 inches of water to cut EC by 50% (in top foot) • 12 inches of water to cut EC by 80% • 24 inches of water to cut EC by 90%• Only effective if water table below 6 to 8 feet
  41. 41. Do amendments help?• Gypsum (calcium sulfate) • Used along with leaching • only effective for sodic soils• Sulfur • May be effective for sodic soils • Limited effectiveness for pH on a landscape scale• Organic matter • Improves soil structure • Does not lower salinity • Does not affect boron levels
  42. 42. Step Back – Big Picture Review
  43. 43. ―Typical‖ Nevada soils• Arid/Droughty conditions • Low precipitation • Coarse, sandy soils• High pH (alkaline – 7 to 8+) • Reduced mineral nutrient release (especially Iron)• Higher evaporation levels produce saline or sodic conditions• May not be able to ―fix‖ the conditions.
  44. 44. IF I CAN’T FIX THE SOIL, WHAT DO I DO?• Choose species adapted to the conditions at hand• Prepare soils for best possible condition
  45. 45. Potting mixes1. Anchorage and stability2. Water3. Nutrients4. Aeration
  46. 46. Possible components• Field soil• Sand• Calcined clay• Perlite• Polystyrene• Peat moss• Pine bark• Hardwood bark• Coconut fiber (coir) Usually combine 2 or more ingredients
  47. 47. Why not field soil alone?1. Anchorage and stability2. Water3. Nutrients4. Aeration
  48. 48. Pots restrict how water drains Gravity
  49. 49. Shift towards soilless potting mixes•Do not need to be pasteurized (sterilized)•Lighter in weight (lower shipping costs)•Mixes are more consistent – you know what to expect
  50. 50. Properties of soilless potting mixes •Water retention •Aeration •DrainageThe goal is to increase aeration without decreasing waterretention.
  51. 51. Coarse mineral components•Perlite • Volcanic origin • Low bulk density • Good drainage and aeration • Low CEC and water-holding•Vermiculite pH 7.5 • Heat-expanded mica • Low bulk density • Use coarse grades for best aeration and drainage • High CEC and water-holding pH 7.5 (U.S.), 9.0 (African) Vermiculite
  52. 52. Sand• Coarse concrete-grade (washed)• High bulk density• Excellent drainage and aeration• Increases water-holding when mixed with bark• Decreases water- holding when mixed with field soil• Low CEC
  53. 53. Calcined Clays • Good water- and nutrient-holding capacity • Excellent drainage qualities • Provides Coarse Texture and Aggregated Structure • Little influence on pH of a mix • Bulk density 30 to 40 lbs/ft 3
  54. 54. Bulk Density•How heavy per unit Bulk density at CC volume Material (lbs/ft3) Field soil 106•Acceptable range: Sand 107 3 40 to 60 lb/ft Sphagnum peat 54•Too heavy: not Coir (coconut fiber) 46 economical to ship Vermiculite 46•Too light: pots with Pine bark 51 Perlite 32 plants topple Rock wool 54 CC = Container Capacity
  55. 55. PeatsLess decomposed • Sphagnum moss - a moss that grows in acid bogs in North America, Canada, and northern Europe • Sphagnum peat moss - the partially decomposed remains of Sphagnum moss • Peat moss (or moss peat) – partially decomposed Sphagnum or hypnum • Reed-sedge peat – reeds, sedges, marsh grasses and cattails (variable in color and other properties) • Peat humus – highly decomposed; lowMore water-holding capacitydecomposed
  56. 56. Sphagnum moss Sphagnum moss peat – pH 3.0 to 4.0 Hypnum moss peat– pH 5.2 to 5.5 Reed-sedge peat – pH 4.0 to 7.5
  57. 57. Peat-based mixes•Common formulations: • Sphagnum peat moss / vermiculite (1 : 1) • Sphagnum peat moss / perlite (1 : 1)•Excellent water- and nutrient-holding, good drainage.•Very difficult to re-wet if allowed to dry out.•Must be careful not to over-fertilize and water enough to leach out excess nutrients.•Breaks down over time.
  58. 58. Coir (coconut) fiber – alternative to peat?• Made from coconut husks.• High water-holding capacity• Excellent drainage• Absence of weeds and pathogens• Decomposes slowly.• Easier to re-wet than Sphagnum peat.• Some sources high in ―Coco Peat‖ salts. pH 4.9 to 6.8
  59. 59. Bark-based products • Cheaper than Sphagnum peat • pH 4.5, increases over time • Excellent aeration and wettability • Poor water-holding • Often mixed with sand and vermiculite or peat moss (3 bark : 1 pH of softwoods 3.0 to 4.0 sand : 1 vermiculite or pH of hardwoods 6.0 to 7.0 peat moss)
  60. 60. Pasteurization• Eliminates disease organisms, insects, nematodes, weeds.• Steam: 160F for 30 min• Soil-based substrates must be pasteurized.• Soilless does not need it unless reused.• Does not protect against future infestation.
  61. 61. Other Pre-plant Additives• Dolomitic limestone • Correct the pH or acidity of a mix• Phosphate • Superphosphate (0-45-0)• Nitrogen and potassium • Enough to last 2 weeks• Micronutrient mix • Enough to last the growing season• Wetting agent • Gel granules help media hold Hydrogel crystals used as a water longer wetting agent
  62. 62. Organic mixes• OMRI – • Organic Materials Review Institute • Assures products are consistent with the requirements of the National Organic Standard.• Challenge is not finding ingredients but in getting consistency.• May not use wetting agents in certified organic products.
  63. 63. Compost and manure rules:Compost 1. Pile must be 131-170F for• Rarely used alone as a 3 days (closed system) to potting ingredient (20 to 15 days (open system). 30% is common). 2. Must be turned at least 5• Has been shown to times. suppress plant diseases. 3. Measure respiration (CO2• During composting process: release, O2 uptake or 1. First phase, most materials easily degraded (104-122F) temperature). 2. Second phase, cellulose and pathogens (and some beneficials) degraded (122- 149F) 3. Third phase, humus content increases, along with some beneficials.
  64. 64. Summary – container substrates• Stable product that will not shrink in volume during plant production / shelf time.• Bulk density low enough for shipping and handling but high enough to prevent toppling of plants.• At least 10 to 20% air by volume at CC (container capacity) in a 6.5-inch pot• High cation exchange capacity (CEC) for nutrient- holding.• pH of 6.2 to 6.8 (soil-based) or 5.4 to 6.5 (soilless) – crop dependent
  65. 65. Questions? Contact: Heidi KratschUniversity of Nevada Cooperative Extension Phone: 775-336-0251 Email: KratschH@unce.unr.edu

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