Soil Chemistry

1
Soil Chemistry

• pH
• soil
• soil solution
• Cation Exchange Capacity
• charge of soil particles

2
Soil pH

• Measure of Hydrogen ion activity
• Acidic-Neutral-Alkaline
• determines availability of nutrients
• buffering - soil resist sudden large changes in pH

3
pH Range

• Note this a
• Logarithmic Scale  based on the
• "powers of ten" 
• pH 6.0 is  10-times  more acidic than pH 7.0
• pH 5.0 is  100-times more acidic than pH 7.0
• 6.5-7.2 is ideal

4
Acidic Soil

• soils in in regions of high rainfall tend to be
  acid
• Cations leach according to strength held
• HgtCagtMggtKgtNH4gtNa
• as cations are leached from soil solution,
  cations on soil particles move into soil solution
  
• H replaces these cations on the soil particle
• pH of soil decreases - becomes more acidic

5
Acidic Soil

• add acid forming materials to soil to amend pH
• peat moss, pine needles
• elemental sulfur, sulfate fertilizers
• form H2SO4 - increase H concentration

6
Alkaline Soil

• increase soil pH with lime (CaCO3)
• in soil solution Ca and OH- (hydroxyl ion)
• Increased Ca concentration displaces H
• H interacts with OH in soil solution
• pH increases - becomes more alkaline

7
Cation Exchange Capacity

• Clay and organic matter have a negative charge
• attract and hold cations
• Cations are attracted/held with different
  strength
• HgtCagtMggtKgtNH4gtNa
• soluble salts - amount of cation salts in soil
  solution

8
Plant Nutritional Requirements

• Depend on
• plant/crop characteristics
• rate of growth - light temperature
• stage of development
• flower, fruiting, rooting
• growing medium - CEC
• amount of rainfall/irrigation
• temperature
• container size - limited reservoir

9
Essential Elements for Plants

• Iron
• Manganese
• Zinc
• Copper
• Boron
• Molybdenum
• Chlorine
• Nickel

• Carbon
• Oxygen
• Hydrogen
• Nitrogen
• Phosphorus
• Potassium
• Calcium
• Magnesium
• Sulfur

10
Remember 17

• C. Hopkins Café Managed by my cousin Mocel
• C H O P K N S Ca Fe Mg B Mn Cu Zn Mo Cl

For a Nickel
11
Nitrogen (N) pg 253

• Plants take up in form of
• NO3-(rarely), NO2-, NH4
• nitrate(NO3-) highly leachable
• Sources
• Ammonium, Nitrate, Urea
• Functions
• synthesis of amino acids, proteins, chlorophyll,
  nucleic acids and coenzymes
• Vegetative growth

12
Phosphorus (P)

• Plants take up as
• H2PO4- orthophosphorus (acid)
• HPO4- monohydrogen phosphate (alkaline)
• Source
• mined apatite (rock phosphate)
• decomposition of organic matter

13
Phosphorus

• Function
• energy (ATP, NADPH) metabolic transfer processes,
  photosynthesis, respiration, nucleic acids
  (genetic material), phospholipids (membranes)
• early maturity (flowers and fruit), root growth,
  stem strength

14
Potassium (K)

• Taken up in elemental form
• Source
• Potassium chloride, Potassium sulfate, potassium
  nitrate
• Function
• sugar and starch formation, synthesis of proteins
• enzyme reactions, osmotic regulation, stomatal
  opening

15
Iron (Fe)

• Function
• chlorophyll synthesis, enzymes, photosynthesis
• Source
• soils
• ferrous sulfates

16
Chelating Agents

• large organic molecule that plant can absorb
• combine with cations to prevent them from
  reacting with anions that would make them
  insoluble and unavailable
• combine with iron, manganese, zinc, copper

17
Determining Requirements

• controlled studies for crop and production
  techniques
• soil test - need to consider availability not
  just presence
• tissue analysis -
• tissue and when it is sampled varies for each crop

18
Nutrient availability

• Amount of nutrient in soil /soil solution
• Form of Nutrient
• Water availability
• pH

19
pH and Nutrient Uptake
20
Nutrient Deficiency

• Mobile N P K Cl Mg
• Immobile B Ca Cu Fe Mn Ni S Zn
• Chlorotic
• Interveinal
• Necrosis
• Stunting
• Handout

21
Photo Websites

• www.hbci.com/wenonah/min-def/list.htm
• http//hort.ufl.edu/nutdef