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Nutrients - Soil Fertility Fruit and Vegetable ScienceK. Jerome

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

  • Essentialelementsneeded 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

  • 3account 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

  • 6used 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 MagnesiumSulfur
  • 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 asionsinstead of elements
  • Ion has positive or negative charge

17.

  • Ion has:
    • positive chargecation
    • 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 rootsabsorbions - soak like a sponge
  • Soil particlesadsorbions - 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 nutrientsfor when growth may be slowed

62.

  • Plants with deep roots, healthy roots need less fertilization

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