At what soil pH is aluminum toxicity rarely a problem?
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Above 5.2.
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At what soil pH is aluminum toxicity rarely a problem?
Above 5.2.
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.
What is one source of hydrogen ions in soil related to sulfur?
Oxidation of sulfur.
How is carbonic acid formed in the soil?
When carbon dioxide gas dissolves in water.
What processes produce high levels of CO2 in soil air?
Root respiration and the decomposition of soil organic matter by microorganisms.
How do fungi respond to soil acidity?
Fungi are versatile and flourish satisfactorily over a wide pH range.
Why do bacteria dominate microbial activity in certain soils?
Bacteria are strong competitors and tend to dominate at intermediate and higher pH levels.
What can make the management of sodic soils difficult?
The cost of calcium supplements.
What happens when active acid sulfate soils are disturbed?
They can release sulfuric acid, leading to soil acidity.
What natural phenomena contribute acids to precipitation?
Lightning, volcanic eruptions, forest fires, and combustion of fossil fuels.
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).
What happens to clay particles when excessive sodium is adsorbed?
The forces that hold clay particles together are greatly weakened.
What is liming in the context of soil management?
The application of lime to alleviate soil acidity.
What is a common type of nitrogen fertilizer that influences soil acidification?
Ammonium-based fertilizers, such as ammonium sulfate and urea.
What should be the first step in managing saline soils?
Intercepting water coming into the problem area.
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.
What happens to sodium when it is displaced in sodic soils?
It is converted to salt (Na2SO4) and leached out of the rooting zone.
What are the typical pH ranges for various types of soils?
They vary and are used to classify soil acidity or alkalinity.
Which bacterium is known to aid in oxidation reactions related to soil acidification?
Thiobacillus ferrooxidans.
What can cause potential soil acidity in certain soils or sediments?
The presence of reduced sulfur.
What types of precipitation can contain acids?
Rain, snow, fog, and dust.
Do different acid functional groups in organic matter dissociate at the same pH level?
No, different groups dissociate at different pH levels.
How can intercepting cropping help in saline soil management?
By using crops like alfalfa to utilize water before it enters problematic areas.
What conditions can cause iron toxicity in its reduced form?
Anaerobic conditions combined with acid pH.
What is the significance of pH values in soil?
They help describe soil acidity or alkalinity.
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.
What soil conditions are required for managing sodic soils?
Good soil drainage and low ground water level.
What is one way ammonium nitrogen affects soil acidity?
Its oxidation can lead to a decrease in soil pH.
What is the second step in managing saline soils after intercepting water?
Mitigation of the actual salinity.
What ions are produced when lime reacts with water?
Ca2+, HCO3-, and OH-.
What does the decomposition of plant residues commonly yield?
Sulfuric acid (H2SO4).
What defines sodic soils?
Excessive levels of sodium (Na+) adsorbed at the cation exchange sites.
What is the primary source of nitrogen and sulfur emissions contributing to soil acidification?
Combustion of fossil fuels in electric power plants and vehicles.
What does pH measure in substances?
The acidity or alkalinity.
What happens to expanding types of clays in sodic soils?
The soil dispersion effect becomes more severe, causing clogging of larger soil pores.
In which agricultural setting can iron toxicity be a problem?
In acid rice paddies.
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.
What is considered the best solution for managing acid sulfate soil?
Avoidance.
At what pH level can iron become toxic to plants?
Usually less than 4.0.
What percentage of the total land area of the Philippines is covered by acidic upland areas?
32 percent.
What occurs to sodium-clay particles when wet?
They easily disintegrate or disperse from larger soil aggregates.
How do organic materials decrease soil pH?
By oxidation of ammonium nitrogen and formation of organic and inorganic acids during decomposition.
How do ammonium-based fertilizers contribute to soil acidification?
They are oxidized by microbes in the soil to produce strong inorganic acids.
Why is organic matter considered a source of H+ ions?
Because it contains numerous acid functional groups from which H+ ions can dissociate.
Where are active acid sulfate soils commonly found?
In coastal areas and regions with high rainfall.
How can improved drainage be achieved in saline soils?
By using infield and boundary field ditches.
What is the most commonly used liming material?
Calcium carbonate (calcitic lime).
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.
What is the electrical conductivity (EC) level in sodic soils?
Less than 4 dS/m.
What does Figure 2 illustrate?
The global distribution of soil acidity and alkalinity.
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.
What happens to plants at pH levels below 4.0 - 4.5?
H+ ions can become toxic, damaging root membranes.
How many hectares of acidic upland areas are there in the Philippines?
About 9.6 million hectares.
What is the most common problem associated with acid soils?
Aluminum toxicity.
What process converts ammonium ions (NH4+) to nitrate ions (NO3-)?
Nitrification.
What characterizes saline soil?
Excessive levels of soluble salts in the soil water that negatively affect plant growth.
What is one method for managing saline soils?
Planting water use efficient crops.
What can be avoided by preserving the wetland condition of Acid Sulfate Soils?
Damage to agricultural crops and acid drainage contamination.
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.
What role do cover crops play in managing saline soils?
They are used during non-crop intervals to support drainage systems.
What is quicklime?
Calcium oxide, a highly reactive liming material.
What is the exchangeable sodium percentage (ESP) in sodic soils?
Greater than 15%.
What role does acid deposition from the atmosphere play in soil acidification?
It contributes to the increase of nitrogen and sulfur in the soil.
What is commonly used as a calcium supplement in sodic soils?
Gypsum.
What types of organic materials can influence soil acidification?
Animal manures, composts, sewage sludge, and some types of plant litter.
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.
Why are Rhizobium bacteria important for legume plants?
They help supply legume plants with nitrogen.
How does aluminum toxicity affect bacteria?
It adversely impacts bacteria involved in nitrogen cycle transformations.
What role do acids play in soil acidification?
Organic and inorganic acids formed during decomposition contribute to lower soil pH.
What color do potential acid sulfate soils often exhibit?
Black color due to iron sulfide compounds.
What is the pH range of sodic (alkali) soils?
Between 8.5 and 10.0.
What is the role of OH- in the lime reaction?
It helps to neutralize H+ ions, reducing acidity.
What is a considerable expense associated with Acid Sulfate Soil?
Attempting to neutralize the acidity.
When does manganese become toxic to plants?
When taken up in excessive quantities.
In which type of soil do fungi predominantly thrive?
In low pH soils.
Why is drainage important in managing saline soils?
Because salts can only be leached downward with soil water.
What beneficial soil bacteria can be killed by high hydrogen ion concentration?
Rhizobium bacteria.
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.
What is the chemical reaction of lime in soil management?
CaCO3 + H2O → Ca2+ + HCO3- + OH-
What are ammonium ions (NH4+) derived from?
Organic matter or most fertilizers.
What is the primary purpose of liming materials?
To reduce soil acidity.
What does the reaction of lime in soil help to neutralize?
Soil acidity.
What type of groups are oxidized during the decomposition of plant residues?
Organic –SH groups.
What are examples of low molecular weight organic acids produced by microbes?
Citric and malic acids.
What is the chemical formula for sulfuric acid?
H2SO4.
What role do organic acids play in soil?
They contribute to the generation of hydrogen ions.
What is the pH range that may provide the most satisfactory plant nutrient levels?
5.5 – 7.0.
Which form of iron is more soluble and can cause toxicity?
The reduced Fe(II) form.
How do plant roots affect soil pH?
Plant roots can alter the pH of the soil.
What happens to sodium-clay particles when the soil dries?
They clog the soil pores, especially macro-pores, and settle down in dense layers.
How does liming affect toxic metals in the soil?
It inactivates toxic metals.
What condition should sulfide-bearing wetland soils be maintained in?
Saturated condition.
What is the pH range of saline soils?
Less than 8.5.
How many hydrogen ions (H+) are released during the oxidation of one ammonium ion (NH4+)?
Two H+ ions.
What do microbes generate as they break down organic matter in the soil?
Many organic acids.
How do low molecular weight organic acids dissociate?
They only weakly dissociate.
What type of conditions do acid soils create for plants?
Plant restricting conditions.
Do symptoms of manganese toxicity vary among plant species?
Yes, symptoms vary among plant species.
What role do humus and clay colloids play in soil acidity?
They hold nonacid cations that can be exchanged with H+ ions.
What is the most common contributor to soil acidity?
The formation of carbonic acid and the dissociation of its H+ ions.
What is the first step in reclaiming sodic soils?
Replace excessive sodium from the cation exchange sites with large amounts of calcium supplements (gypsum).
What is an active acid sulfate soil?
A type of soil that contains iron sulfides and can produce sulfuric acid when disturbed.
What is one principle of liming?
Neutralization of soil acidity.
What is the best solution for managing Acid Sulfate Soil?
Avoidance, specifically preventing S oxidation.
What conditions favor microbial activity that accelerates soil acidification?
Warm, moist conditions.
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.
What are the consequences of saline soil on crops?
Reduced crop yields and potential plant death under severe conditions.
What is the most common symptom of aluminum toxicity in plants?
A stunted root system with short, thick, stubby roots.
What is dolomitic lime?
A liming material that contains both calcium carbonate and magnesium carbonate.
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.
What elements are mobilized by acid mine drainage that affect aquatic life?
Iron and aluminum.
At what pH level does manganese become increasingly soluble?
At levels as high as 5.6.
What happens to nonacid cations during soil acidification?
They can be exported in leaching water along with accompanying anions.
What role do microorganisms play in soil acidification?
They facilitate oxidation reactions, making them proceed thousands of times faster.
How is soil acidity quantified?
Using the pH scale.
What are the environmental impacts of active acid sulfate soils?
They can lead to acidification of water bodies and harm aquatic life.
What are two examples of ammonium-based fertilizers?
Ammonium sulfate [(NH4)2SO4] and urea [CO(NH2)2].
What is acid mine drainage?
An extremely acid and toxic brew formed as water percolates through oxidizing materials.
How much limestone is needed to neutralize the acidity from the oxidation of 1 kg of sulfur?
About 3 kg of limestone.
What benefits does maintaining wetland conditions provide?
It preserves natural habitats for diverse wild plants and animals.
What is the pH value that defines acid soils?
Less than 5.5 for most of the year.
What impact does pH shock have on aquatic communities?
It can devastate the aquatic community.
What is manganese's role in plants?
Manganese is an essential plant nutrient.
What does the pH scale express in relation to soil?
The activity or concentration of H+ ions present in a solution.
What effect does liming have on nutrient availability?
It increases the availability of nutrients.
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).
What is the typical pH range of acid mine drainage?
0.5 – 2.0.
What is the electrical conductivity (EC) level in saline soils?
Greater than 4 dS/m.
What mineral is mentioned as a source of reduced sulfur?
Pyrite.
What deficiency is commonly found in acid soils?
Molybdenum.
What is the role of magnesium in dolomitic lime?
It helps to correct magnesium deficiencies in the soil.
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.
What are some examples of sulfur compounds found in coastal sediments?
Pyrite (FeS2), iron monosulfides (FeS), and elemental sulfur (S).
What acids are commonly found in precipitation?
Sulfuric and nitric acids.
Which Archaeon is associated with facilitating oxidation reactions in soil acidification?
Ferroplasma acidipilum.
Why is neutralization of acid sulfate soil often impractical in the field?
Because of the enormous amounts of CaCO3 required.
What is the benefit of using lime in agriculture?
Improves soil structure and nutrient availability.
What ions dominate the exchange complex in acidic soils?
Acid cations such as H+ and Al3+.
What is the role of microbial activity in nitrification?
Microbial oxidation converts ammonium ions to nitrate ions.
What process does soil sodicity cause?
Degradation of soil structure through soil dispersion.
What is the exchangeable sodium percentage (ESP) in saline soils?
Less than 15%.
What types of soluble salts are found in saline soils?
High levels of Ca, Mg, and Na sulfates, chlorides, and bicarbonates.
How do acids in precipitation affect soil?
They contribute H+ ions to the soil.
What happens when acid mine drainage reaches a stream?
Iron sulfates dissolved in the drainage water continue to produce acid by oxidation and hydrolysis.
What is hydrated lime?
Calcium hydroxide, produced by adding water to quicklime.
What is the effect of lime on soil pH?
It raises the soil pH, making it less acidic.
What characteristics do roots exhibit under aluminum toxicity?
Little branching or growth of laterals.
What toxicities are associated with acid soils?
Aluminum and Iron.
What are common symptoms of manganese toxicity in plants?
Crinkling or cupping of leaves and interveinal patches of chlorotic tissue.
What causes soils to become acidic?
When H+ ions exchange with nonacid cations like Ca2+, Mg2+, K+, and Na+.
What are stronger acids produced from litter breakdown?
Carboxylic and phenolic acid groups in humus.
What type of soluble salt is predominant in sodic soils?
High sodium carbonate (Na2CO3).
