Olds College LHAP Soil Reaction pH powerpoint
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Soil Reaction pH powerpoint

Soil and Water/Soil Reaction pH powerpoint .pptx

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Slide 1 Soil Reaction: pH Chemical Properties of Soil Slide 2 Soil pH (Reaction) pH is a measure of the Hydrogen ion concentration of the soil solution Slide 3 Soil Reaction (pH) Water DISSOCIATES into H+ and OH- ions In pure water, these concentrations are EQUAL (neutral) At neutral the pH is 7 pH LESS THAN 7 indicated a greater concentration of the H+ (acid) pH GREATER THAN 7 there is a higher concentration of OH- (alkaline/basic) Number is negative logarithm of hydrogen concentration pH of 4 is a hydrogen concentration of 0.0001 mol/liter Slide 4 Soil pH is a MASTER VARIABLE that affects soil chemical and biological properties Schill Slide 5 pH is correlated with: the SOLUBILITY of nutrient compounds and hence, their availability to plants Slide 6 pH is correlated with: organism populations and the levels of their activity the rate and degree of organic matter decomposition Slide 7 pH is correlated with: nitrogen mineralization (the nitrogen in organic matter is converted into inorganic material: ammonium NH4+ Slide 8 pH is correlated with: base saturation: the extent to which the cation exchange sites are saturated with cations other than H+ Slide 9 Cations on Clay Surfaces the proportion of bases to the TEC (Total Cation Exchange Capacity) is termed BASE SATURATION this is expressed as a % the GREATER the base saturation the HIGHER the pH value (more alkaline) Slide 10 pH of 7 cannot assume that a pH of 7 infers 50% base saturation the PROPORTION of bases to hydrogen for a pH of 7 will vary from one soil to another The pH at a given base saturation is also dependent on: the kind of clay present the adsorbed cations on the clay Slide 11 Alkaline Soils Soils will become alkaline if… they are over limed They are irrigated with alkaline water The parent material is calcium rich CaCO3 and MgCO3 develop (in arid conditions) Slide 12 Acid Soils Soils become acidic for one of 4 reasons Rainfall and leaching of base cations Organic matter decay resulting in organic acids Harvest of crops Acidic parent material Slide 13 Factors that Lower pH Lower pH results from the formation of carbonic acid from the dissolved carbon dioxide in soil water Slide 14 Factors that Lower pH the deposition of sulfur compounds through “acid rain” Slide 15 Plant Nutrients Primary Macro Nutrients Nitrogen NH4+, NO3 - Phosphorous H2PO4-, HPO4 -2 Potassium K+ Secondary Macro Nutrients Calcium Ca +2 Magnesium Mg +2 Sulfur SO4-2 Micro Nutrients Iron Fe +2, Fe +3 Copper Cu+2 Zinc Zn +2 Manganese Mn +2 Molybdenum MoO4 -2 Boron BO3-3,H3BO3 Chlorine Cl - Slide 16 Significance of Soil Reaction(pH) AVAILABILITY OF NUTRIENTS The most desirable pH for maximum solubility (availability) is about 6.5 to 7.5 Slide 17 Significance of Soil Reaction(pH) AVAILABILITY OF NUTRIENTS as pH increases the availability of calcium, magnesium, and potassium in the soil solution increases. Slide 18 Significance of Soil Reaction(pH) AVAILABILITY OF NUTRIENTS Nitrogen and Sulfur reach a maximum availability above about 5.5 and nitrogen starts to lose availability at a high pH. Slide 19 Significance of Soil Reaction(pH) AVAILABILITY OF NUTRIENTS Micronutrient most soluble at lower pH values less soluble at higher pH ( except Molybdenum ) Slide 20 Significance of Soil Reaction(pH) AVAILABILITY OF NUTRIENTS Phosphorus gets tied up with calcium in soils about 8-8.4 At 8.5, where sodium is the dominant cation it is available again. Loses availability below 5.5 Slide 21 Significance of Soil Reaction(pH) SOIL ORGANISMS AND THEIR ACTIVITIES Soil pH near 7 is best for the widest range of soil microorganisms Bacteria, algae, fungi and actinomycetes are all quite active Slide 22 Significance of Soil Reaction(pH) SOIL ORGANISMS AND THEIR ACTIVITIES As pH DECREASES the fungi increase in dominance as the bacteria and actinomycetes decrease in abundance and activity Result: decrease in organic matter decomposition Slide 23 Significance of Soil Reaction(pH) SOIL ORGANISMS AND THEIR ACTIVITIES Nitrifying bacteria are also inhibited when the pH is less than 5.5 Slide 24 Significance of Soil Reaction(pH) Mycorrhizal Fungi will thrive in the pH most suitable to their host plant For many that is a more acidic pH Slide 25 Pools of Soil Acidity Active Acidity H+ activity in the soil SOLUTION exchangeable on the colloids (clay & organic matter) have immediate effect on soil pH H+ H+ H+ H+ H+ H+ H+ Shazral Slide 26 Pools of Soil Acidity Reserve Acidity H+ is BOUND by organic matter and clays like these barnacles to rock Slide 27 Buffering Capacity Ability to resist a change in pH ensures stability in the soil pH prevents drastic fluctuations in pH It takes less material to change the pH in a sandy soil Slide 28 Alkaline Soils usually contain calcium and magnesium carbonates above pH of 8.4, usually sodium carbonates and bicarbonates The carbonates must be dissolved if alkaline soil is to be made neutral Slide 29 Acidifying the Soil Many soils have few exchangeable hydrogen and much exchangeable Calcium, Magnesium and sometimes Sodium Slide 30 Acidifying Materials Sulfur is the cheapest and most commonly used material Slide 31 2S + 3O2 + 2H2O 2H2So4 4H++ 2SO42- Step 1: microorganisms convert S into Sulfuric Acid Step 2: this then combines with the carbonate materials H2SO4 + CaCO3 CaSO4 + H2O +CO2 Step 3: when all the carbonate materials have been dissolved the Sulfuric acid can thenreact with cations on the clay and OM surfaces colloid = Ca+2+H2SO4 colloid =H+ CaSo4 It takes about 6 to 8 weeks for sulfur to act during the summer Slide 32 Altering pH To lower pH apply: Sulfur Organic Matter Slide 33 Acidifying Materials Peat - 1 m3 has the same acidifying power as 300-650g of Sulfur Fertilizers - use acidifying fertilizers when you need to add nutrients (not to just alter the pH -if you add too much you will have salinity problems and possible toxicities) Slide 34 Acidifying Materials Iron (ferrous) Sulfate don’t use it regularly though as the IRON will reduce the availability of Phosphorus Slide 35 Ammonium fertilizers will acidify soil through the following reaction: NH4+ + 3O2 2N2O- + 2H2O +4H+ 2N2O- + O2 2NO3 Ammonium based fertilizers will not change pH of alkaline soil for many years Slide 36 Altering pH To raise pH add Lime Lime contains Calcium and Magnesium carbonates the rate of application depends on a soil’s CEC, the texture and the initial pH Slide 37 Raising the pH: Liming can use calcium carbonate the more finely ground, the more rapid the pH changes Slide 38 Origin of Carbonates In most cases the parent material constitutes the initial source of carbonates,either because they already existed there, or because although they were not originally present, the carbonates have formed in the soil as a result of the weathering of original minerals rich in calcium Slide 39 Test for Carbonates Soils with Calcium Carbonates (calcareous material) will effervesce (fizz) when a few drops of 10%HCl is added to the soil. Slide 40 We often plant in this calcareous layer Slide 41 We often plant in this calcareous layer

Slide Outline

Extracted text and images from the presentation.

Slide 1

Soil Reaction: pH

Chemical Properties of Soil

Slide 2

Soil pH (Reaction)

pH is a measure of the Hydrogen ion concentration of the soil solution

image1.png

Slide 3

Soil Reaction (pH)

Water DISSOCIATES into H+ and OH- ions

In pure water, these concentrations are EQUAL (neutral)

At neutral the pH is 7

pH LESS THAN 7 indicated a greater concentration of the H+ (acid)

pH GREATER THAN 7 there is a higher concentration of OH- (alkaline/basic)

Number is negative logarithm of hydrogen concentration pH of 4 is a hydrogen concentration of 0.0001 mol/liter

Slide 4

Soil pH

is a MASTER VARIABLE that affects soil chemical and biological properties

Schill

image6.jpg image9.png

Slide 5

pH is correlated with:

the SOLUBILITY of nutrient compounds

and hence, their availability to plants

image5.png image11.png

Slide 6

pH is correlated with:

organism populations and the levels of their activity

the rate and degree of organic matter decomposition

image3.png

Slide 7

pH is correlated with:

nitrogen mineralization

(the nitrogen in organic matter is converted into inorganic material: ammonium NH4+

image12.png image4.png

Slide 8

pH is correlated with:

base saturation:

the extent to which the cation exchange sites are saturated with cations other than H+

image7.png

Slide 9

Cations on Clay Surfaces

the proportion of bases to the TEC (Total Cation Exchange Capacity) is termed BASE SATURATION

this is expressed as a %

the GREATER the base saturation the HIGHER the pH value (more alkaline)

image8.png image15.png

Slide 10

pH of 7

cannot assume that a pH of 7 infers 50% base saturation

the PROPORTION of bases to hydrogen for a pH of 7 will vary from one soil to another

The pH at a given base saturation is also dependent on:

the kind of clay present

the adsorbed cations on the clay

Slide 11

Alkaline Soils

Soils will become alkaline if…

they are over limed

They are irrigated with alkaline water

The parent material is calcium rich

CaCO3 and MgCO3 develop (in arid conditions)

image10.jpg image19.png image21.png

Slide 12

Acid Soils

Soils become acidic for one of 4 reasons

Rainfall and leaching of base cations

Organic matter decay resulting in organic acids

Harvest of crops

Acidic parent material

image20.png

Slide 13

Factors that Lower pH

Lower pH results from the formation of carbonic acid from the dissolved carbon dioxide in soil water

image22.png image22.png

Slide 14

Factors that Lower pH

the deposition of sulfur compounds through “acid rain”

image13.png

Slide 15

Plant Nutrients

Primary Macro Nutrients Nitrogen NH4+, NO3 - Phosphorous H2PO4-, HPO4 -2 Potassium K+

Secondary Macro Nutrients Calcium Ca +2 Magnesium Mg +2 Sulfur SO4-2

Micro Nutrients Iron Fe +2, Fe +3 Copper Cu+2 Zinc Zn +2 Manganese Mn +2 Molybdenum MoO4 -2 Boron BO3-3,H3BO3 Chlorine Cl -

image16.png

Slide 16

Significance of Soil Reaction(pH)

AVAILABILITY OF NUTRIENTS

The most desirable pH for maximum solubility (availability) is about 6.5 to 7.5

image17.png

Slide 17

Significance of Soil Reaction(pH)

AVAILABILITY OF NUTRIENTS

as pH increases the availability of calcium, magnesium, and potassium in the soil solution increases.

image17.png

Slide 18

Significance of Soil Reaction(pH)

AVAILABILITY OF NUTRIENTS

Nitrogen and Sulfur reach a maximum availability above about 5.5 and nitrogen starts to lose availability at a high pH.

image17.png

Slide 19

Significance of Soil Reaction(pH)

AVAILABILITY OF NUTRIENTS

Micronutrient most soluble at lower pH values

less soluble at higher pH ( except Molybdenum )

image17.png image14.png image23.png image24.png

Slide 20

Significance of Soil Reaction(pH)

AVAILABILITY OF NUTRIENTS

Phosphorus gets tied up with calcium in soils about 8-8.4

At 8.5, where sodium is the dominant cation it is available again.

Loses availability below 5.5

image17.png

Slide 21

Significance of Soil Reaction(pH)

SOIL ORGANISMS AND THEIR ACTIVITIES

Soil pH near 7 is best for the widest range of soil microorganisms

Bacteria, algae, fungi and actinomycetes are all quite active

image17.png

Slide 22

Significance of Soil Reaction(pH)

SOIL ORGANISMS AND THEIR ACTIVITIES

As pH DECREASES the fungi increase in dominance as the bacteria and actinomycetes decrease in abundance and activity

Result: decrease in organic matter decomposition

image17.png

Slide 23

Significance of Soil Reaction(pH)

SOIL ORGANISMS AND THEIR ACTIVITIES

Nitrifying bacteria are also inhibited when the pH is less than 5.5

image30.png

Slide 24

Significance of Soil Reaction(pH)

Mycorrhizal Fungi will

thrive in the pH most

suitable to their host

plant

For many that is a more acidic pH

image28.jpg

Slide 25

Pools of Soil Acidity

Active Acidity

H+ activity in the soil SOLUTION

exchangeable on the colloids (clay & organic matter)

have immediate effect on soil pH

H+

H+

H+

H+

H+

H+

H+

Shazral

image41.png image25.png

Slide 26

Pools of Soil Acidity

Reserve Acidity

H+ is BOUND by organic matter and clays like these barnacles to rock

image26.png image25.png

Slide 27

Buffering Capacity

Ability to resist a change in pH

ensures stability in the soil pH

prevents drastic fluctuations in pH

It takes less material to change the pH in a sandy soil

image33.png image37.png

Slide 28

Alkaline Soils

usually contain calcium and magnesium carbonates

above pH of 8.4, usually sodium carbonates and bicarbonates

The carbonates must be dissolved if alkaline soil is to be made neutral

Slide 29

Acidifying the Soil

Many soils have few exchangeable hydrogen and much exchangeable Calcium, Magnesium and sometimes Sodium

image10.jpg image19.png image39.png

Slide 30

Acidifying Materials

Sulfur is the cheapest and most commonly used material

image10.jpg image19.png image27.png image16.png

Slide 31

2S + 3O2 + 2H2O 2H2So4 4H++ 2SO42-

Step 1: microorganisms convert S into Sulfuric Acid

Step 2: this then combines with the carbonate materials

H2SO4 + CaCO3 CaSO4 + H2O +CO2

Step 3: when all the carbonate materials have been dissolved the Sulfuric acid can thenreact with cations on the clay and OM surfaces

colloid = Ca+2+H2SO4 colloid =H+ CaSo4

It takes about 6 to 8 weeks for sulfur to act during the summer

Slide 32

Altering pH

To lower pH apply:

Sulfur

Organic Matter

image38.png image25.png

Slide 33

Acidifying Materials

Peat - 1 m3 has the same acidifying power as 300-650g of Sulfur

Fertilizers - use acidifying fertilizers when you need to add nutrients (not to just alter the pH -if you add too much you will have salinity problems and possible toxicities)

image31.png

Slide 34

Acidifying Materials

Iron (ferrous) Sulfate

don’t use it regularly though as the IRON will reduce the availability of Phosphorus

image29.png

Slide 35

Ammonium fertilizers will acidify soil through the following reaction:

NH4+ + 3O2 2N2O- + 2H2O +4H+

2N2O- + O2 2NO3

Ammonium based fertilizers will not change pH of alkaline soil for many years

Slide 36

Altering pH

To raise pH add Lime

Lime contains Calcium and Magnesium carbonates

the rate of application depends on a soil’s CEC, the texture and the initial pH

image36.png image25.png

Slide 37

Raising the pH: Liming

can use calcium carbonate

the more finely ground, the more rapid the pH changes

image10.jpg image19.png image39.png

Slide 38

Origin of Carbonates

In most cases the parent material constitutes the initial source of carbonates,either because they already existed there, or because although they were not originally present, the carbonates have formed in the soil as a result of the weathering of original minerals rich in calcium

Slide 39

Test for Carbonates

Soils with Calcium Carbonates (calcareous material) will effervesce (fizz) when a few drops of 10%HCl is added to the soil.

Slide 40

We often plant in this calcareous layer

image35.jpg image32.png image34.jpg

Slide 41

We often plant in this calcareous layer

image40.jpg image32.png