Soil Science Part 2

What is the vadose zone?

Unsaturuated zone above the water table

What is the water table?

The upper surface of the zone of saturation

What is groundwater?

Subsurface water within the saturated zone

What does SPAC mean? What is it?

It stand for Soil-Plant-Atmosphere continuum and is the process of water entering the soil wither being evaporated into the atmosphere, absorbed by plants, or moved/stored within the soil

What is evapotranspiration?

Evaporation from the surface plus the transpiration from plants

What is the potential evapotranspiration?

The amount of water that would evaporate from the surface and be transpired by plants if that water is at an optimal level

What is percolation? When does it cause losses?

THe downward movement of water through the soil. Losses by percolation are caused when input exceeds the holding capacity leading to drainage

What is the infiltration rate? What influences it?

THe rate which water enters the soil from the surface. It is influenced by soil properties, vegetation cover, soil management, slope, and rainfall characteristics

What makes a soil waterlogged?

All or nearly all pores are filled with water

What is a wetland? What types of soil is found there?

An area of land that is a transitional zone between aquatic and terrestrial systems. It has hydrocarbons and hydrophytes

How do people cause artificial drainage?

For contruction, infrastructure, and agriculture

What is soil air? What influences it?

The ventilation and gas exchange between the soil and the atmosphere. It is influenced by soil macroporosity, soil water content, and organism oxygen uptake

What is the oxidation-reduction potential?

The process of one compound losing an electron becoming oxidized and those electrons going to another compound causing it to be reduced

What are the ecological effects of aeration?

It effects the rates of organic decay, plant growth, and oxidation-reduction conditions

What is pH?

Acidity and alkalinity based on the balance between hydrogen and hydroxyl

What are soil colloids?

Organic and inorganic matter with a very small particle size and large surface area

What are the general properties of soil colloids?

The surface of the colloid carries electrostatic charges, adsorption of cations and anions, and adsorption of water

What are the four different types of soil colloids?

Crystalline silicate clays, non-crystalline silicate clays, iron/aluminum oxides, and organic colloids

How are silicate clays developed?

The weathering of minerals

What are the properties of crystalline silicate clays?

They are composed of silicon, oxygen, and aluminum and are mostly negatively charged

What is the structure of silicate clays?

THey often come in either tetrahedral sheet with a silicon surrounded by 4 oxygen atoms or octahedral sheets with an aluminum surrounded by 6 oxygens

What are the five groups of silicate clays?

Kaolinite, Smectite, vermiculite, chlorite, and fine-grained micas

Of the five types of silicate clays, which one does not have a 2:1 sheet structure or two tetrahedral sheets around an octahedral sheet?

Kaolinite

Of the five types of cilicate clays which ones expand?

Smectite and vermiculite

What silicate clay is the most expansive?

Smectite

Which silicate clay has strongly bonded water and ions in between its layers?

Vermiculite

What are two types of oxides? How are they formed?

Iron and aluminum. Both are formed from weathering of silicate minerals

What is the structure of oxides? Do they have tetrahedral sheets?

An octahedral sheets with iron or aluminum atoms and 6 oxygens. They lack tetrahedral sheets

Are oxides expansive?

No, they are not expansive

What makes up organic colloids?

They are made of decomposed organic matter. They have a carbon ring structure and carbon chains with exposed hydroxyl groups

What are the two sources of charges in soil colloids>

Permanent or constant charge that occurs through isomorphic substitution and a pH-dependent charge which is based on the pH

What is isomorphic substitution?

The replacement of an atom by another of similar size without disrupting/changing the crystal structure of the mineral

What occurs in pH-dependent charges?

As the pH increases the crystal releases H+ from functional group and a negative charge results

Do most colloids have a positive or negative charge?

Negtive charge where they attract cations and repel anions

Where does ion adsorption occur in colloids?

Outer-sphere complexes where there is an attraction for water molecules between the ion and colloid. The inner-sphere complex where the ion directly binds to the colloid

Which complex’s bond between ion and colloid is stronger: inner or outer?

Inner as it is binding directly to the colloid

What does the ratio law assume in colloids?

At equilibrium, the ratio of ions on the colloid will be the same as the ratio of ions in the solution

What is cation selectively in colloids?

Same cations are bond more tightly depending on their valence number, the strength of the charge’s negative site, and the size of the hydrated ion

Other than ratio law and cation selectivity, what two other principles govern cation exchange?

Reversibility stating that reactions are reversible and charge equivalence stating that exchange is on a charge-for-charge basis

What is the cation exchange capacity?

The sum total of exchangeable cationic charges a soil can adsorb

What type of colloid has the highest level of cec and why?

Organic colloids as they have more negative sites available meaning that there is a higher rate of cec

What is anion exchange?

Anion exchange is similar to cation exchange but the colloid surface charges are positive, the exchangeable ions are negative, and it increases with decreasing pH

What is pH buffering?

A resistance of changes that occurs when an acid or base is added

Does pH buffering increase or decrease with CEC?

It increases

What are the three ranges of plant growth in relation to nutrient concentration?

Deficiency range, sufficiency range, and toxicity range

What is liming? What influences its amount?

Lime is a material used to neutralize soil acidity that is influenced by the amount of desired pH, the buffering capacity, the chem comp of the liming materials, and the fineness of the material

What is the difference between autotrophs and heterotrophs?

Autotrophs obtain carbon from carbon dioxide or carbonates while heterotrophs obtain carbon from the breakdown of organic materials produced by other organisms

What are the levels that make up the trophic levels?

The 1st level is primary producers such as plants and other autotrophs. the 2nd level is primary consumers who eat the autotrophs, the 3rd level is secondary consumers who eat lower consumers

What affect do soil macro-organisms have on the soil?

Through burrowing they alter air/water flow, mix soil profile, alter soil structure, create channels for plant roots, and eat vegetation

Are earthworms, insects, and termites macro-organisms or microorganisms

They are small macro-organisms

What effects do plant roots have on soil?

It competes for oxygen, is a source of carbon/energy for soil organisms, influences chem/physical soil properties as a source of SOM, uptaking water/nutrients, and exuding nutrients

How do microorganisms affect the soil?

Plant rely on them for SOM/nutrients cycling and chemical transformations however they also compete for nutrients and oxygen

What do soil fungis do for the soil?

Fungi decomposes SOM, nutrient cycles, produces beneficial/toxic organic, and produces diseases

What benefits do mycorrhizae offer to fungi and plants?

They provide food to fungi and reach into pores plant roots can’t reach, improve water/nutrient uptake, and may protect against toxicity

What are nematodes? What do they do?

They are microscopic unsegmented worms that feed on fungi, bacteria, algae, and some plant distributing microbes

Where are the largest pools of carbon?

The crust in carbonate rocks and in oceans

How much are carbon does soil contain than vegetation and the atmosphere combined?

2 times as much

What is the soil carbon cycle?

Plants take up CO2 from the atmosphere through photosynthesis, products used in respiration are released or stored, primary consumers eat plants and exhale CO2, dead plants/animals return to the soil where they decompose and release CO2

What does the C/N ratio mean?

It helps determine that levels of carbon vs nitrogen in an ecosystem and the rate of decay occurring

What is a nitrate depression period?

A period after the addition of fresh SOM where decomposers have removed most of the soluble nitrate from the soil solution

What role does SOM hold in soils?

It assists in soil aggregation, the infiltration rate, CEC, is a source of food, releases/cycles nutrients, and affects soil colour

How is the nutrient supply maintained around roots?

Root interception where roots grow towards nutrient sources, mass flow where nutrient move with the flow of water, and diffusion where random motions of nutrients in solutions enter the roots

Why is nitrogen such an important aspect in soils and in plants?

It is a major part of all proteins including enzymes, nucleic acids, and chlorophyll

What is nitrogen fixation?

The conversation of atmospheric nitrogen into ammonium which is oxidized into nitrate for plant usage through nitrification

What is nitrogen mineralization?

THe conversion of an element from an organic form to an inorganic form through microbial decomposition

What is nitrogen immobilization?

The conversion of an element from an inorganic form into an organic form in microbial or plant tissues

What is denitrification?

The reduction of nitrate to gaseous nitrogen mostly done by anaerobic bacteria

How does phosphorus benefit plant growth?

It is a macronutrient used in ATP, DNA, RNA, and more

Why is phosphorus which a tricky mineral?

Too little phosphorus in the soil inhibits plant growth but at high levels plants can no longer absorb it leaving it to sit in the soil and bind to surrounding nutrients like iron and calcium

What is the depletion zone?

The concentration of elements in soil solution has been reduced by plant uptake being faster than diffusion can replace the element

What are the four major pools is the potassium cycle?

Soil solution, exchangeable in the cation exchange, non-exchangeable, and structural/mineral

How is potassium added or lost in its cycle?

It is added through weathering, SOM, and fertilizer and lost by erosion, runoff, leaching, and harvesting

Between nitrogen, phosphorous, and potassium which on does not cause eutrophication?

Potassium

What are the biggest forms of losses for potassium?

Leaching when cation exchange sites are held by other cations and liming due to cation selectivity

What is luxury consumption in relation to potassium?

Luxury consumption occurs when plants intake more nutrients than is needed depressing other cations and causing nutritional imbalance

How big is the micronutrient sufficiency range?

The sufficiency range is narrow as plants only need a small amount of micronutrients

What are the four goals of nutrient management?

Cost-effective production of high quality organisms, maintence/enhancement of soil health, efficient use/conversion of nutrient resources, and protection of the environment past soil

What is the law of the minimum?

Production and growth are limited by its lowest resource and cannot be higher than it

What are the types of water erosion?

Sheet erosion that removes a uniform layer, rill erosion where sheet slow concentrates into small channels, and gully erosions where water accumulates in narrow channels that are larges than rills

What factors play into universal soil loss?

Rainfall erosivity, soil erodibility, topographic factors, cover and management, and erosion-control practices

What are soil-related loss factors?

Soil erodibility factor which states how susceptible the soil is to erosion and the topographic factor which includes how the sloop length and its steepness affect soil erosion

What are management-related factors in the universal loss equation?

Cover and management factor which is the ratio loss under current practice vs bare soil and support practice factor which is the ratio of soil loss under current practices vs if crops were present

What are forms of off-site damages?

Pollution, sediment damage, and windblown sand and dust damage