Nutrients   soil fertility
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Nutrients - Soil Fertility

Nutrients - Soil Fertility
Fruit and Vegetable Science
K. Jerome

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Nutrients soil fertility Presentation Transcript

  • 1. SOIL FERTILITY
  • 2.
    • Ability of soil to supply nutrients for plant growth  
  • 3.    
    • Soil is storehouse of nutrients   Some available, some not
  • 4. Soil fertility:  
    • quantity of nutrients soil contains
    • how well protected from leaching
    • how available to plant
    • how easily roots can take them up
  • 5. Plant nutrients  
    • Essential elements needed for plant growth
  • 6. Plant nutrients
    • Plants absorb 90 elements
    • Only a few needed for growth
    • Some not needed by plants but by animals that eat plants (cobalt)
    • Others not needed, can be toxic (lead)
  • 7.  
  • 8.
    • How to determine which are essential?
  • 9. Essential plant elements
    • 1. lack of element stops plant from growth or reproduction
    • 2. element is directly involved in plant processes
    • 3. shortage of element can only be corrected by supplying that element  
  • 10. 17 essential elements  
    • 3 account for 95% plant needs
    • carbon, oxygen and hydrogen
    • come from water, air
  • 11. Non-minerals         Macronutrients Air and Water Carbon (C)       Hydrogen (H)       Oxygen (O)
  • 12. 14 come from soil  
    • 6 used in large amounts:
    • macronutrients
    • Nitrogen Calcium
    • Phosphorus Magnesium
    • Potassium Sulfur
  • 13. Primary Macronutrients  
    • Nitrogen Phosphorus Potassium
    • Not always available in large enough quantities
    • Add by fertilizing
  • 14. Secondary Macronutrients  
    • Calcium Magnesium Sulfur
    • Soil usually has plenty
  • 15.   Micronutrients
    • 8 nutrients left
    • Used in small amounts
    • Plant won't grow normally without them
  • 16.   NUTRIENT IONS
    • Plants absorb some of the nutrients as ions instead of elements
    • Ion has positive or negative charge
  • 17.
    • Ion has:
      • positive charge cation
      • negative charge anion
  • 18.  
    • Ions form in soil when compounds dissolve in water   Example:
    • Potassium nitrate (fertilizer) dissolves in water,
    • molecule breaks down into potassium ion and nitrate ion
  • 19.  
    • Plant roots absorb ions - soak like a sponge
    • Soil particles adsorb ions - hold on to them - stick to it
  • 20.  
  • 21. SOURCES OF ELEMENTS IN SOIL
    • Nutrient elements present in soil in four places (pools)
  • 22. SOURCES OF ELEMENTS IN SOIL
    • 1. soil minerals
    • major source
    • released slowly by weathering
    • not source of nitrogen
    •  
  • 23. SOURCES OF ELEMENTS IN SOIL
    • 2. organic matter
    • large amounts of nitrogen
    • nutrient anions
    • released by decay   
  • 24. SOURCES OF ELEMENTS IN SOIL
    • 3. adsorbed nutrients
    • held by clay and humus particles
    • relatively available to plants
  • 25. SOURCES OF ELEMENTS IN SOIL
    • 4. dissolved ions
    • ions in soil solution
    • plants absorb directly
    • may be leached
  • 26.  
  • 27. Soil colloids    
    • Tiny particles of clay and humus with slight electrical charge
    • This charge attracts plant nutrient ions
  • 28.   CATION EXCHANGE  
    • Negative charge on soil colloids:
      • attracts positively charge ions
      • repels negatively charged ions
  • 29. adsorption  
    • Negatively charged colloid attracts swarm of cations from soil solution
  • 30.  
  • 31.  
  • 32. Cation Exchange
    • When one ion taken up by plant (pulled off soil particle), replaced by another.
    • Replacement of one cation for another
  • 33.  
    • Ability of soil to hold nutrients –
    • directly related to the number of cations it can attract to soil colloids
    • Determined by the amount of clay and humus in soil mix
  • 34.
    • Displacement of cations depends on:
    • Relative concentration
    • high concentration displaces low
    • The number of charges on a cation
  • 35. high CHARGE displaces low Al>Ca>Mg>K>Na
  • 36.  
  • 37.
    • Plant roots have negatively charged surfaces
    • positively charged hydrogen ions attached
    • Cation exchange takes place when plant roots exchange positive hydrogen ions for cations on soil colloids or in solution
  • 38.   Cation Exchange Capacity (CEC)
    • The ability of soil to hold exchangable ions
    • CEC expressed in milligram equivalents per 100 grams of soil (mEq/100g)
  • 39.  
  • 40. Bonding strength  
    • If two cations are present in soil in equal numbers
    • one that bonds most strongly will be adsorbed
    • others will be leached out
  • 41. Mass action 
    • more ions in soil,
    • more exchange sites it will occupy
  • 42.  
    • Weakly held cations are more available for plant uptake
  • 43.
    • A clay particle is covered with negative charges
    • Opposites attract, ions with positive charge(s) stick all over surface of clay
    • root hairs secrete
    • H+ into water around clay particles
    • Smaller H cations
    • replace larger cations
  • 44.  
    • Several nutrients available to plants as negatively charged ions – anion exchange
    • Negative charge means it is repelled from cation exchange site
    • Anion exchange greatest in acid soils
  • 45. Implications for Growing  
    • High CEC soils have more clay
    • Low CEC soils more sand
  • 46.  
  • 47.   Herbicide
    • CEC determines how much herbicide should be used.
    • Colloids absorb pesticides also, tie them up.
    • High CEC, clay soils usually need more to get effect you want
  • 48. Fertilization  
    • High CEC soils have greater ability to hold nutrients - larger amounts, less frequently
    • Low CEC - smaller amounts more frequently - leach out
  • 49.  
    • Golf courses - all sand - low CEC - fertilize lightly and often
    • Greenhouses - soilless - low CEC - fertilize lightly and often
  • 50.  
    • Improve CEC by adding organic matter
    • Clay soils need less organic matter except to aerate soil
  • 51. NUTRIENT UPTAKE  
  • 52. Nutrient absorption  
    • Nutrient ions cross cell membranes of root cells and move into vascular system
  • 53.
    • Some uptake is passive
    • Most uptake is active - takes energy to pull nutrients into high concentration already in plant  
  • 54.  
    • Roots produce energy by respiration
    • Waterlogged soil limits respiration - limits nutrient uptake
  • 55.  
    • Root hairs get ions from soil solution by their own form of cation and anion exchange
  • 56.  
    • As root tips grow, move through solution, constantly finding more nutrients
  • 57.  
    • Capillary action moves nutrients through solution toward plant roots
  • 58.  
    • Diffusion
    • moves ions through soil solution
    • – higher concentration to lower concentration
  • 59. Factors affecting uptake  
    • Anything interfering with photosynthesis - slows growth, slows uptake   --low light --poor drainage --soil compaction --dry soils --soil temperature
  • 60.  
  • 61. Luxury Consumption
    • Plants can sometimes store nutrients for when growth may be slowed
  • 62.    
    • Plants with deep roots, healthy roots need less fertilization