p.18
Human Influenced Soil Acidification
What happens when oxygen is introduced into normally anaerobic soils containing sulfur?
Oxidation of the sulfur may produce large amounts of acidity, forming acid sulfate soil.
p.6
Sources of Hydrogen Ions in Soil
How is carbonic acid formed in the soil?
When carbon dioxide gas dissolves in water.
p.6
Sources of Hydrogen Ions in Soil
What processes produce high levels of CO2 in soil air?
Root respiration and the decomposition of soil organic matter by microorganisms.
p.29
Effects of Soil Acidity on Plants
How do fungi respond to soil acidity?
Fungi are versatile and flourish satisfactorily over a wide pH range.
p.29
Effects of Soil Acidity on Plants
Why do bacteria dominate microbial activity in certain soils?
Bacteria are strong competitors and tend to dominate at intermediate and higher pH levels.
p.43
Management Strategies for Sodic Soils
What can make the management of sodic soils difficult?
The cost of calcium supplements.
p.20
Human Influenced Soil Acidification
What happens when active acid sulfate soils are disturbed?
They can release sulfuric acid, leading to soil acidity.
p.11
Sources of Hydrogen Ions in Soil
What natural phenomena contribute acids to precipitation?
Lightning, volcanic eruptions, forest fires, and combustion of fossil fuels.
p.28
Effects of Soil Acidity on Plants
What nutrients are reduced in strongly acid soils?
Calcium (Ca), Magnesium (Mg), Potassium (K), Phosphorus (P), Nitrogen (N), Sulfur (S), Molybdenum (Mo), and Boron (B).
p.37
Effects of Sodic Soils on Soil Structure
What happens to clay particles when excessive sodium is adsorbed?
The forces that hold clay particles together are greatly weakened.
p.30
Management of Soil Acidity
What is liming in the context of soil management?
The application of lime to alleviate soil acidity.
p.14
Human Influenced Soil Acidification
What is a common type of nitrogen fertilizer that influences soil acidification?
Ammonium-based fertilizers, such as ammonium sulfate and urea.
p.41
Management Strategies for Saline Soils
What should be the first step in managing saline soils?
Intercepting water coming into the problem area.
p.40
Effects of Sodic Soils on Soil Structure
How do sodic soils compare to saline soils in terms of erosion susceptibility?
Sodic soils are more susceptible to wind and water erosion compared to saline soils.
p.44
Management Strategies for Sodic Soils
What happens to sodium when it is displaced in sodic soils?
It is converted to salt (Na2SO4) and leached out of the rooting zone.
p.5
Acid Soils Characteristics
What are the typical pH ranges for various types of soils?
They vary and are used to classify soil acidity or alkalinity.
p.19
Human Influenced Soil Acidification
Which bacterium is known to aid in oxidation reactions related to soil acidification?
Thiobacillus ferrooxidans.
p.18
Human Influenced Soil Acidification
What can cause potential soil acidity in certain soils or sediments?
The presence of reduced sulfur.
p.11
Sources of Hydrogen Ions in Soil
What types of precipitation can contain acids?
Rain, snow, fog, and dust.
p.8
Sources of Hydrogen Ions in Soil
Do different acid functional groups in organic matter dissociate at the same pH level?
No, different groups dissociate at different pH levels.
p.42
Management Strategies for Saline Soils
How can intercepting cropping help in saline soil management?
By using crops like alfalfa to utilize water before it enters problematic areas.
p.27
Effects of Soil Acidity on Plants
What conditions can cause iron toxicity in its reduced form?
Anaerobic conditions combined with acid pH.
p.5
Acid Soils Characteristics
What is the significance of pH values in soil?
They help describe soil acidity or alkalinity.
p.8
Sources of Hydrogen Ions in Soil
How does the accumulation of organic matter affect soil acidity?
It tends to acidify the soil by facilitating the loss of nonacid nutrient cations and providing a source of H+ ions.
p.43
Management Strategies for Sodic Soils
What soil conditions are required for managing sodic soils?
Good soil drainage and low ground water level.
p.15
Human Influenced Soil Acidification
What is one way ammonium nitrogen affects soil acidity?
Its oxidation can lead to a decrease in soil pH.
p.41
Management Strategies for Saline Soils
What is the second step in managing saline soils after intercepting water?
Mitigation of the actual salinity.
p.33
Saline and Sodic Soils Overview
What defines sodic soils?
Excessive levels of sodium (Na+) adsorbed at the cation exchange sites.
p.16
Human Influenced Soil Acidification
What is the primary source of nitrogen and sulfur emissions contributing to soil acidification?
Combustion of fossil fuels in electric power plants and vehicles.
p.5
Acid Soils Characteristics
What does pH measure in substances?
The acidity or alkalinity.
p.40
Effects of Sodic Soils on Soil Structure
What happens to expanding types of clays in sodic soils?
The soil dispersion effect becomes more severe, causing clogging of larger soil pores.
p.12
Sources of Hydrogen Ions in Soil
What happens when a plant root takes in a positive charge?
It can maintain charge balance by either taking up a negative charge or exuding a positive charge as a different cation.
p.37
Effects of Sodic Soils on Soil Structure
What occurs to sodium-clay particles when wet?
They easily disintegrate or disperse from larger soil aggregates.
p.15
Human Influenced Soil Acidification
How do organic materials decrease soil pH?
By oxidation of ammonium nitrogen and formation of organic and inorganic acids during decomposition.
p.14
Human Influenced Soil Acidification
How do ammonium-based fertilizers contribute to soil acidification?
They are oxidized by microbes in the soil to produce strong inorganic acids.
p.8
Sources of Hydrogen Ions in Soil
Why is organic matter considered a source of H+ ions?
Because it contains numerous acid functional groups from which H+ ions can dissociate.
p.20
Acid Soils Characteristics
Where are active acid sulfate soils commonly found?
In coastal areas and regions with high rainfall.
p.41
Management Strategies for Saline Soils
How can improved drainage be achieved in saline soils?
By using infield and boundary field ditches.
p.31
Management of Soil Acidity
What is the most commonly used liming material?
Calcium carbonate (calcitic lime).
p.18
Human Influenced Soil Acidification
What is the result of drainage or excavation in soils with potential acid sulfate materials?
It can lead to the formation of acid sulfate soils due to increased acidity.
p.13
Acid Soils Characteristics
What does Figure 2 illustrate?
The global distribution of soil acidity and alkalinity.
p.40
Effects of Sodic Soils on Soil Structure
What is a major effect of sodic soils on physical structure?
They result in soils that are difficult to till, poor seed germination, and restricted plant root growth.
p.26
Effects of Soil Acidity on Plants
What happens to plants at pH levels below 4.0 - 4.5?
H+ ions can become toxic, damaging root membranes.
p.4
Acid Soils Characteristics
How many hectares of acidic upland areas are there in the Philippines?
About 9.6 million hectares.
p.33
Saline and Sodic Soils Overview
What characterizes saline soil?
Excessive levels of soluble salts in the soil water that negatively affect plant growth.
p.42
Management Strategies for Saline Soils
What is one method for managing saline soils?
Planting water use efficient crops.
p.23
Management of Soil Acidity
What can be avoided by preserving the wetland condition of Acid Sulfate Soils?
Damage to agricultural crops and acid drainage contamination.
p.35
Effects of Saline Soils on Plant Growth
What happens when a solution has low osmotic potential due to high soluble salt concentration?
Plant roots cannot extract water from the soil, causing drought-like symptoms in the plants.
p.42
Management Strategies for Saline Soils
What role do cover crops play in managing saline soils?
They are used during non-crop intervals to support drainage systems.
p.31
Management of Soil Acidity
What is quicklime?
Calcium oxide, a highly reactive liming material.
p.16
Human Influenced Soil Acidification
What role does acid deposition from the atmosphere play in soil acidification?
It contributes to the increase of nitrogen and sulfur in the soil.
p.15
Human Influenced Soil Acidification
What types of organic materials can influence soil acidification?
Animal manures, composts, sewage sludge, and some types of plant litter.
p.41
Management Strategies for Saline Soils
What is crucial to assess when dealing with high water tables in saline soils?
The source of the water that contributes to the high water table.
p.26
Effects of Soil Acidity on Plants
Why are Rhizobium bacteria important for legume plants?
They help supply legume plants with nitrogen.
p.24
Effects of Soil Acidity on Plants
How does aluminum toxicity affect bacteria?
It adversely impacts bacteria involved in nitrogen cycle transformations.
p.15
Human Influenced Soil Acidification
What role do acids play in soil acidification?
Organic and inorganic acids formed during decomposition contribute to lower soil pH.
p.19
Human Influenced Soil Acidification
What color do potential acid sulfate soils often exhibit?
Black color due to iron sulfide compounds.
p.32
Management of Soil Acidity
What is the role of OH- in the lime reaction?
It helps to neutralize H+ ions, reducing acidity.
p.23
Management of Soil Acidity
What is a considerable expense associated with Acid Sulfate Soil?
Attempting to neutralize the acidity.
p.25
Effects of Soil Acidity on Plants
When does manganese become toxic to plants?
When taken up in excessive quantities.
p.41
Management Strategies for Saline Soils
Why is drainage important in managing saline soils?
Because salts can only be leached downward with soil water.
p.8
Sources of Hydrogen Ions in Soil
What happens to nonacid nutrient cations like Ca2+ and Mg2+ due to organic matter?
They form soluble complexes with organic matter, leading to their loss by leaching.
p.32
Management of Soil Acidity
What is the chemical reaction of lime in soil management?
CaCO3 + H2O → Ca2+ + HCO3- + OH-
p.9
Sources of Hydrogen Ions in Soil
What are ammonium ions (NH4+) derived from?
Organic matter or most fertilizers.
p.7
Sources of Hydrogen Ions in Soil
What role do organic acids play in soil?
They contribute to the generation of hydrogen ions.
p.12
Sources of Hydrogen Ions in Soil
How do plant roots affect soil pH?
Plant roots can alter the pH of the soil.
p.37
Effects of Sodic Soils on Soil Structure
What happens to sodium-clay particles when the soil dries?
They clog the soil pores, especially macro-pores, and settle down in dense layers.
p.30
Management of Soil Acidity
How does liming affect toxic metals in the soil?
It inactivates toxic metals.
p.7
Sources of Hydrogen Ions in Soil
How do low molecular weight organic acids dissociate?
They only weakly dissociate.
p.2
Acid Soils Characteristics
What type of conditions do acid soils create for plants?
Plant restricting conditions.
p.25
Effects of Soil Acidity on Plants
Do symptoms of manganese toxicity vary among plant species?
Yes, symptoms vary among plant species.
p.17
Sources of Hydrogen Ions in Soil
What role do humus and clay colloids play in soil acidity?
They hold nonacid cations that can be exchanged with H+ ions.
p.6
Sources of Hydrogen Ions in Soil
What is the most common contributor to soil acidity?
The formation of carbonic acid and the dissociation of its H+ ions.
p.43
Management Strategies for Sodic Soils
What is the first step in reclaiming sodic soils?
Replace excessive sodium from the cation exchange sites with large amounts of calcium supplements (gypsum).
p.20
Acid Soils Characteristics
What is an active acid sulfate soil?
A type of soil that contains iron sulfides and can produce sulfuric acid when disturbed.
p.30
Management of Soil Acidity
What is one principle of liming?
Neutralization of soil acidity.
p.23
Management of Soil Acidity
What is the best solution for managing Acid Sulfate Soil?
Avoidance, specifically preventing S oxidation.
p.22
Management of Soil Acidity
What role does calcite play in managing acid sulfate soil?
Calcite acts as a neutralizing agent that can react with sulfuric acid from sulfur oxidation to form gypsum.
p.33
Saline and Sodic Soils Overview
What are the consequences of saline soil on crops?
Reduced crop yields and potential plant death under severe conditions.
p.24
Effects of Soil Acidity on Plants
What is the most common symptom of aluminum toxicity in plants?
A stunted root system with short, thick, stubby roots.
p.31
Management of Soil Acidity
What is dolomitic lime?
A liming material that contains both calcium carbonate and magnesium carbonate.
p.42
Management Strategies for Saline Soils
What types of crops can be grown in poorly drained saline soils?
Late maturing, deep rooted, and salt tolerant crops like alfalfa, sugar beet, and sunflower.
p.25
Effects of Soil Acidity on Plants
At what pH level does manganese become increasingly soluble?
At levels as high as 5.6.
p.17
Sources of Hydrogen Ions in Soil
What happens to nonacid cations during soil acidification?
They can be exported in leaching water along with accompanying anions.
p.19
Human Influenced Soil Acidification
What role do microorganisms play in soil acidification?
They facilitate oxidation reactions, making them proceed thousands of times faster.
p.20
Effects of Soil Acidity on Plants
What are the environmental impacts of active acid sulfate soils?
They can lead to acidification of water bodies and harm aquatic life.
p.14
Human Influenced Soil Acidification
What are two examples of ammonium-based fertilizers?
Ammonium sulfate [(NH4)2SO4] and urea [CO(NH2)2].
p.21
Human Influenced Soil Acidification
What is acid mine drainage?
An extremely acid and toxic brew formed as water percolates through oxidizing materials.
p.23
Management of Soil Acidity
What benefits does maintaining wetland conditions provide?
It preserves natural habitats for diverse wild plants and animals.
p.2
Acid Soils Characteristics
What is the pH value that defines acid soils?
Less than 5.5 for most of the year.
p.21
Human Influenced Soil Acidification
What impact does pH shock have on aquatic communities?
It can devastate the aquatic community.
p.25
Effects of Soil Acidity on Plants
What is manganese's role in plants?
Manganese is an essential plant nutrient.
p.4
Sources of Hydrogen Ions in Soil
What does the pH scale express in relation to soil?
The activity or concentration of H+ ions present in a solution.
p.30
Management of Soil Acidity
What effect does liming have on nutrient availability?
It increases the availability of nutrients.
p.35
Effects of Saline Soils on Plant Growth
How does soil water flow in relation to osmotic potential?
Soil water flows from higher osmotic potential (low salt concentration) to lower osmotic potential (high salt concentration).
p.31
Management of Soil Acidity
What is the role of magnesium in dolomitic lime?
It helps to correct magnesium deficiencies in the soil.
p.35
Effects of Saline Soils on Plant Growth
What is the primary effect of excessive soluble salts on plants?
It limits the ability of plant roots to absorb soil water, even in wet conditions.
p.18
Human Influenced Soil Acidification
What are some examples of sulfur compounds found in coastal sediments?
Pyrite (FeS2), iron monosulfides (FeS), and elemental sulfur (S).
p.11
Sources of Hydrogen Ions in Soil
What acids are commonly found in precipitation?
Sulfuric and nitric acids.
p.22
Management of Soil Acidity
Why is neutralization of acid sulfate soil often impractical in the field?
Because of the enormous amounts of CaCO3 required.
p.31
Management of Soil Acidity
What is the benefit of using lime in agriculture?
Improves soil structure and nutrient availability.
p.17
Sources of Hydrogen Ions in Soil
What ions dominate the exchange complex in acidic soils?
Acid cations such as H+ and Al3+.
p.9
Sources of Hydrogen Ions in Soil
What is the role of microbial activity in nitrification?
Microbial oxidation converts ammonium ions to nitrate ions.
p.33
Saline and Sodic Soils Overview
What process does soil sodicity cause?
Degradation of soil structure through soil dispersion.
p.34
Saline and Sodic Soils Overview
What types of soluble salts are found in saline soils?
High levels of Ca, Mg, and Na sulfates, chlorides, and bicarbonates.
p.11
Sources of Hydrogen Ions in Soil
How do acids in precipitation affect soil?
They contribute H+ ions to the soil.
p.21
Human Influenced Soil Acidification
What happens when acid mine drainage reaches a stream?
Iron sulfates dissolved in the drainage water continue to produce acid by oxidation and hydrolysis.
p.31
Management of Soil Acidity
What is hydrated lime?
Calcium hydroxide, produced by adding water to quicklime.
p.31
Management of Soil Acidity
What is the effect of lime on soil pH?
It raises the soil pH, making it less acidic.
p.24
Effects of Soil Acidity on Plants
What characteristics do roots exhibit under aluminum toxicity?
Little branching or growth of laterals.
p.25
Effects of Soil Acidity on Plants
What are common symptoms of manganese toxicity in plants?
Crinkling or cupping of leaves and interveinal patches of chlorotic tissue.
p.17
Sources of Hydrogen Ions in Soil
What causes soils to become acidic?
When H+ ions exchange with nonacid cations like Ca2+, Mg2+, K+, and Na+.
p.7
Sources of Hydrogen Ions in Soil
What are stronger acids produced from litter breakdown?
Carboxylic and phenolic acid groups in humus.
p.34
Saline and Sodic Soils Overview
What type of soluble salt is predominant in sodic soils?
High sodium carbonate (Na2CO3).
