Garden Soils and Fertilizer for Community Gardens


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Ward Upham, Rapid Response Center and Extension Master Gardener Coordinator
Kansas Community Gardens Conference, July 8-9, 2013

This class will cover the properties of garden soil, why those properties are important and how to improve soil so that it will grow healthier, more productive plants. Fertilizers and their use will also be covered.

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  • Most people think about the first first but overlook anchorage and oxygen is not often emphasized. Every living cell in a plant must have oxygen. So, how good your soil is depends on how well it provides these four things.
  • Pore space is vital for a good soil. A good soil would have about 50% pore space.
  • Saturated soil eliminates oxygen. Most plants will die within a week if the soil is completely saturated.
  • The structure of a soil is how it holds together. A clay soil with good structure will break into small particles called peds that are much like grape nuts. These peds allow the formation of large pore spaces while maintaining very good water and nutrient holding capacity.
  • This is the broken down parent material.
  • Doesn’t matter what the original material was; could have been limestone or flint. All that matters is the size.
  • Note how surface area increases as you move from silt to clay.
  • Think of “hooks” as being able to hold nutrients. A sand-based green has few hooks and therefore cannot hold many nutrients. Therefore, sand-based greens are often spoon-fed. Eight hooks on the original piece but 64 on the smaller blocks.
  • If a soil loses structure, it loses pore space
  • Should always strip off topsoil and store it until all grading is done. Then return it.
  • Adding organic matter to improve soils.
  • If this is a heavy soil, you have formed a “pot.” The planting hole will fill with water and the tree may drown.
  • Area is a square because tiller is on back of garden tractor and too difficult to make circle.
  • Note that organic matter does not go all the way to edge. Therefore, organic matter feathers out toward the outside edges. Roots do not like to go from one type of soil to another. This gradual reduction from modified to unmodified soil encourages roots to leave the planting area.
  • The width of the bar does not show how much of that element is in the soil but rather how available that element is to the plant.
  • Lime is calcium carbonate and gypsum is calcium sulfate. Calcium raises pH and sulfate lowers it. They cancel one another out.
  • Garden Soils and Fertilizer for Community Gardens

    1. 1. Garden Soils & Fertilizer
    2. 2. What does soil provide? –Nutrients . . . . . eat –Water . . . . . . . Drink –Anchorage . . . hold on - Oxygen ………Breathe
    3. 3. Soil Is More Than Just Weathered Rock Organic Matter 25% Air 5% 25% Water 45% Mineral Matter
    4. 4. SOIL COMPONENTS: Air • Every living cell in a plant needs oxygen. • Oxygen level drops as you go deeper into the soil. Atmosphere is 21% oxygen. • Anything less than 3% oxygen in soil and roots die. • Need 5-10% oxygen for roots to grow. • Need 12-18% oxygen for new roots to form.
    5. 5. SOIL COMPONENTS: Air • Even trees have 80 to 90% of their roots in the top foot of soil. Not Like This But Like This
    6. 6. Soil Components Organic Matter 5% 50% Water 45% Mineral Matter
    7. 7. SOIL COMPONENTS: Air • Some trees tolerant of flooding such as red maple, pin oak and cottonwood • Others aren’t such as pines and red oak • Turf isn’t tolerant of flooding and will usually die within a week or sooner
    8. 8. Soil Components Organic Matter 25% Air 5% 25% Water 45% Mineral Matter
    9. 9. Soil Components Organic Matter 25% Air 5% 25% Water Organic Matter • Smallest % • Plant and animal residue • Helps build & maintain structure • Source of mineral elements 45% Mineral Matter
    10. 10. Soil Components Organic Matter 25% Air 5% 25% Water 45% Mineral Matter
    11. 11. Soil Components Organic Matter 25% Air 5% 25% Water •Minerals • Inorganic particles • Classified according to size • Sand – largest • Silt – medium • Clay – smallest • Soil texture 45% Mineral Matter
    12. 12. Soil Texture • Soil texture - the proportion of sand, silt and clay. Separate Diameter (mm) Number of particles/g Surface area/g (cm2) Very coarse sand 2-1 90 11 Coarse sand 1 – 0.5 720 23 Medium sand 0.5 – 0.25 5,700 45 Fine sand 0.25 – 0.10 46,000 91 Very fine sand 0.10 – 0.05 722,000 227 Silt 0.05 – 0.002 5,776,000 454 Clay <0.002 90,260,853,000 8,000,000
    13. 13. Surface Area Same volume, twice the surface area
    14. 14. Surface Area More surface, more “hooks”
    15. 15. Soil Texture • Estimate by rolling slightly moist soil in fingers – Firm ball, smooth and becomes sticky when moistened, forms a long ribbon  too much clay – Won’t stay together very well and feels gritty  good soil for most landscape plants – Won’t stay together at all and feels very coarse  too sandy
    16. 16. Advantages and Disadvantages of Different Soils • Sandy Soils • Clay Soils
    17. 17. SANDY SOIL • Advantages: – Good aeration – Good drainage – Good heat convection – Good water infiltration – Less prone to compaction • Disadvantages – Excessive evaporation – Requires extra water and fertilization • Droughty - Poor water holding capacity • Leaches readily
    18. 18. CLAY SOIL • Advantages – High nutrient and water holding capacity • Disadvantages – Poor internal (vertical) drainage – Slow to dry out – Slow to warm up – Puddles when wet – Crusts as it dries – Becomes compacted if it is worked when wet – High “Shrink/Swell” capacity
    19. 19. Photosynthesis & Respiration • Photosynthesis Makes the food for the plant and stores it in plant tissues. Requires water from the soil. • Respiration Breaks the food down into the basic building blocks for plant health and growth. Requires oxygen from the soil and gives off carbon dioxide into the soil.
    20. 20. Soil Aeration • Soils must contain sufficient large pore space to allow oxygen to penetrate to the deepest of roots and carbon dioxide to exit from the soil.
    21. 21. Soil Aeration Get the good gas in and the bad gas out
    22. 22. Soil Structure • The arrangement of primary soil particles into aggregates (like grape nuts) • Soil particles vary in size and how tightly they are held together • Soil structure is a factor of texture and organic matter content
    23. 23. SOIL STRUCTURE • Aggregates: form mainly as a by-product of soil microorganisms that use organic matter as their food • Can improve soil structure by adding organic matter • Think “sugar cubes.”
    24. 24. Organic Matter Improves Problem Soils • Organic matter gives a clay soil some of the good characteristics of a sandy soil such as better aeration and a faster water infiltration rate. • Organic matter also acts as a sponge in sandy soils so they are better able to hold water and nutrients
    25. 25. Aeration Management • Promote soil particle aggregation • Maintain large, open pore spaces • Avoid destructive practices • Don’t smash the sugar cubes ! •If you must, then supply some glue to reform them.
    26. 26. WAYS TO RUIN SOIL STRUCTURE • Compact the soil • Work the soil when wet
    27. 27. WAYS TO RUIN SOIL STRUCTURE • Compact the soil • Work the soil when wet • Pulverize with excessive tillage
    28. 28. • Soil structure is destroyed and horizons are mixed during home construction
    29. 29. Aeration Management • Maintain high organic matter in the soil
    30. 30. Organic Matter Decomposed or partially decomposed plant and animal remains “Humus” is organic matter that has lost its’ original identity
    31. 31. ADDING Organic Matter • Mix thoroughly with underlying soil but don’t go quickly from amended soil to undisturbed soil • Steps – Till deeply – Add organic matter (2 to 4 inches or more) – Till again just enough to mix; don’t create pockets or layers
    32. 32. • 2 to 4 inches of amendment should be incorporated into the top 6 inches of soil
    33. 33. Adding Organic Matter When Planting a Tree • Do NOT add organic matter just to the soil that came out of the planting hole.
    34. 34. Adding Organic Matter When Planting a Tree • Mark off 10’ x 10’ area for tree.
    35. 35. Adding Organic Matter When Planting a Tree • Till area
    36. 36. Adding Organic Matter When Planting a Tree • Add organic matter
    37. 37. Adding Organic Matter When Planting a Tree • Till again
    38. 38. Adding Organic Matter When Planting a Tree • Plant Tree
    39. 39. Adding Amendments Other than Organic Matter • Gypsum • Sand • Expanded Shale
    40. 40. What About Gypsum? • Gypsum is calcium sulfate. • Has no effect on pH. • Will work on sodic soils; those that are high in sodium. • Sodic soils are not common; usually have a pH between 8.5 to 10.0. • In other soils, will not hurt but also will not help unless the soil is deficient in calcium or sulfur.
    41. 41. What About Sand? • Sand has limited value as a soil amendment - and can create more problems than it solves • To be of benefit, enough sand must be added to exceed the “threshold” at which pore space begins to increase - around 80% of the soil • Sand below the threshold level only occupies air filled pores (And can result in a form of concrete)
    42. 42. What About Expanded Shale? • Expanded shale is ground shale passed through a kiln at 2000 degrees C. As the shale cools, cavities are left that can hold water and air. • Add 3 inches to the surface of a problem soil and till 6 to 8 inches deep • Recommended for heavy, clay soils only
    43. 43. Chemical Properties • pH – The degree of acidity or alkalinity of a soil
    44. 44. Nutrient availability is greatly influenced by pH
    45. 45. Chemical Properties • Adjusting pH – Lime increases pH • gypsum does not affect pH – Sulfur will also lower pH but at a slow rate
    46. 46. How Sulfur Works • Powdered sulfur does not change pH directly • Certain bacteria oxidize sulfur and this oxidized sulfur changes the pH • Ideal temps are between 75 and 104 degrees • Soil should be moist • Small particle size of sulfur helps speed reaction • Several months are often needed for most of the reaction to take place
    47. 47. Calcareous Soils • Some soils have little particles of limestone (calcium carbonate) mixed in. These are called calcareous soils • All free calcium carbonate must be neutralized with sulfur before the pH will change • Often it is not practical to change the pH of a calcareous soil.
    48. 48. Is Your Soil Calcareous? • Can do simple test to find out • Add a few drops of vinegar to a small quantity of dry soil – If it fizzes vigorously, the soil is 3% calcium carbonate or higher – A mild fizz suggests between 1 and 2% calcium carbonate – A fizz that is heard but not seen suggests less than 1% calcium carbonate
    49. 49. How Much Sulfur for a Calcareous Soil? • Need 1 pound of sulfur to neutralize 3 pounds of calcium carbonate • Assume 80 pounds per cubic foot of soil • You would need 26 pounds of sulfur per 100 square feet to neutralize each 1% of calcium carbonate
    50. 50. So What Do You Do With a Calcareous Soil • Sulfur Method: Add 50 pounds of elemental sulfur per 1000 square feet in the spring before planting and mix into the soil. • Chelated Iron Method: Add EDDHA. – Sequestar 6% Iron Chelate WDG – Sequestrene 138 – Millers FerriPlus • Chelated iron can be mixed into the soil or applied as a drench
    51. 51. Fertilizers
    52. 52. FERTILIZER ANALYSIS • Sequence of Three Numbers: Reflects the percentage by weight of nitrogen, phosphorus and potassium – in that order
    53. 53. ROLE OF PRIMARY MACRONUTRIENTS Nitrogen: Growth and green color Phosphorus: Seedling germination and growth, root development, flowering and fruit development Potassium: Toughness and ability to withstand stress
    54. 54. Basic Info on Fertilization • Normally key off the amount of nitrogen because it is needed most frequently and often in greatest amounts • Phosphorus and potassium levels are much more stable in soil and are added as called for in soil test • Native Kansas soils usually have adequate potassium (artificial soils, such as golf greens, may not)
    55. 55. COMPLETE FERTILIZER • Contains some of each primary macronutrient – 12-12-12 – 13-13-13 – 5-10-5 – 6-24-24 – 8-32-16 – 10-10-10
    56. 56. COMPLETE BALANCED FERTILIZER • Contains all primary macronutrients in the same proportion – 12-12-12 – 13-13-13 – 10-10-10
    57. 57. How Much Fertilizer To Add Want 1lb Nitrogen/1,000 sq ft = ? Lbs 10-10-10 1 lb/1,000 sq ft = 10 lbs 10% N 33-10-10 1 lb/1,000 sq ft = 3.03 lbs 33% N 20-10-10 1 lb/1,000 sq ft = 5 lbs 20% N
    58. 58. How Much Fertilizer To Add Lawn = 15,000 sq ft How many lbs of 27-3-3 will you need to fertilize the lawn at a rate of 1.5 lbs/1,000 sq ft? 27-3-3 1.5 lb/1,000 sq ft = 5.55 lbs/1,000 sq ft 27% N 5.55 x 15 = 82.5 lbs for 15,000 sq ft.
    59. 59. How Much Fertilizer To Add Want to fertilize a 5,000 sq ft garden with 1 lb N/1,000 sq ft using 20-5-5 fertilizer. How many lbs of fertilizer will you need to buy? 20-5-5 1 lb/1,000 sq ft = 5 lbs/1,000 sq ft 20% N 5 lbs x 5 = 25 lbs for 5,000 sq ft.
    60. 60. Thank You