Transcript Chapter 8 The Colliodal Fraction: Chapter 9: Soil Acidity Kaolinite Mica Montmorillonite Fulvic acid THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C.

Chapter 8 The Colliodal Fraction:
Chapter 9: Soil Acidity
Kaolinite
Mica
Montmorillonite
Fulvic acid
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Figure 8.1
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Figure 8.4
Basic Phyllosilicate
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Important Clays Minerals
• Kaolinite – Most common in soils
• Smectite – Shrink-Well Clays
– Montmorillonite
• Vermiculite
• Micas – Fine-grained micas
– Illite
• Chlorite
• Humus – Humic acid and organic matter
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Figure 8.27
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Figure 8.12
Structure of Humic Acid
THE NATURE AND PROPERTIES OF SOILS, 13/e
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Figure 8.10
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Genesis of Soil Colloids
• Alteration – An example would be the change from
muscovite mica to fine-grained mica through physical
breakdown, loss of some elements and addition of others.
• Recrystallization – Results from the complete
breakdown of the original crystal structure and regrowth of
clay minerals.
• Relative Stages of Weathering – Fine-grained micas
are an early stage while kaolinite and iron oxides are late
stages
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Figure 8.14
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Principles Governing Cation Exchange
Reactions
• Reversibility – A cation is usually replaced by a
hydrogen ion and this reaction is reversible
Micelle*Na+ + H+ = Micelle*H+ + Na+
• Charge Equivalence – Exchanges take place on a
charge-by-charge basis
Micelle*Ca2+ + 2H+ = Micelle*2H+ + Ca2+
• Ratio Law – The amount of exchangeable cation in the
soil solution will affect the ion’s equilibrium
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Principles Governing Cation Exchange
Reactions
• Mass Action – If a product precipitates, volatilizes, or
strongly associates with an anion, the reaction is not
reversible.
• Cation Selectivity – Higher charge and hydrated
radius affect the exchangeability of cations
Al3+ > Ca2+ > Mg2+ > K+ = NH4+ > Na+
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Figure 8.19
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Figure 8.22
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Figure 8.20
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
CEC and pH in Soil Orders
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Figure 8.23
Relation of CEC to pH
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Acidifying a Soil
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Pools of Soil Acidity
• Active Acidity
– H+ ion activity in the soil solution.
• Exchangeable (Salt Replaceable) Acidity
– Associated with exchangeable aluminum and hydrogen ions
in the parent material.
– The take the place of beneficial cations.
• Residual Acidity
– Hydrogen and Aluminum ions bound to organic matter and
clays. May free-up Cation exchange locations with liming
– May be 100,000 times greater acid input than the other pools
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Pools of Acid
THE NATURE AND PROPERTIES OF SOILS, 13/e
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Acid Rain
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Geographic Distribution of Acid Rain
THE NATURE AND PROPERTIES OF SOILS, 13/e
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Effect of Soil pH on Root Growth
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Plant Macronutrients
• Calcium and Magnesium are essential to plants
and are tied to soil acidity
• Calcium
– Calcium is second only to N and K as a plant
macronutrient
– Used in cell walls, cell elongation, membrane
permeability, and enzymes
– Taken up exclusively by young root tips and
redistributed in the plant with transpiration water
– Symptoms: Young leaves not unfolding, lack of root
development, blossom-end rot, empty peanut shells
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Symptoms of Low Calcium
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Plant Macronutrients
• Magnesium
–
–
–
–
Taken up in less quantity than Calcium
Used in the Chlorophyll molecule
Used in the synthesis of oils, proteins, and enzymes
Symptoms: Mottled green and yellow coloring in the
older leaves.
• Both Calcium and Magnesium deficiencies can be
remedied by applying lime (CaO) or Gypsum
(CaSo4*2H2O)
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Principle Pathways of Calcium and Magnesium
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
Calcium and Magnesium Cycle
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
THE NATURE AND PROPERTIES OF SOILS, 13/e
Nyle C. Brady and Ray R. Weil
©2002 Pearson Education, Inc.
Upper Saddle River, New Jersey 07458