©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Chapter 8 The Colliodal Fraction: Chapter 9: Soil Acidity Kaolinite Mica Montmorillonite Fulvic acid

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 8.1

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 8.4 Basic Phyllosilicate

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil 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

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 8.27

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 8.12 Structure of Humic Acid

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 8.10

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil 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

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 8.14

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil 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*Ca H + = Micelle*2H + + Ca 2+ Ratio Law – The amount of exchangeable cation in the soil solution will affect the ion’s equilibrium

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil 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 Al 3+ > Ca 2+ > Mg 2+ > K + = NH 4 + > Na +

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 8.19

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 8.22

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 8.20

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil CEC and pH in Soil Orders

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 8.23 Relation of CEC to pH

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Acidifying a Soil

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil 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

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Pools of Acid

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Acid Rain

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Geographic Distribution of Acid Rain

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Effect of Soil pH on Root Growth

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil 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

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Symptoms of Low Calcium

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil 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 (CaSo 4 *2H 2 O)

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Principle Pathways of Calcium and Magnesium

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Calcium and Magnesium Cycle

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil