Soil Ecology Final Study Guide ENVS 223

____(a)______ is stored in rock and thus generally available on young soils with ready access to weathered parent materials. _______(b)_______ is stored in the atmosphere and thus is generally *unavailable* on young soils.

(a) Phosphorus (b) Nitrogen

What is "immobilization" of nitrogen or phosphorus?

During immobilization, microorganisms convert inorganic forms to organic phosphate, which are then incorporated into their living cells. Mineralization and immobilization of phosphorus occur simultaneously in the soil. Ultimately, the C:P. ratio determines whether there is net mineralization or net immobilization. immobilization is the reverse of mineralization. All living things require N; therefore microorganisms in the soil compete with crops for N. Immobilization refers to the process in which nitrate and ammonium are taken up by soil organisms and therefore become unavailable to crops.

What is special about AM and EM fungi?

Fungal symbiont - mutualism; plant and fungus give each other benefits. A mycorrhiza is a mutualistic relationship between a fungus and a plant. The fungus grows in or on the plant roots. The fungus benefits from the easy access to food made by the plant. The plant benefits because the fungus puts out mycelia that helps absorb water and nutrients. AM fungi & EM fungi: like a good infection, they connect to all different plants providing nutrients. Arbuscular mycorrhizal (AM) plants and fungi associate with lower soil organic matter, higher pH, lower phosphorus and higher nitrogen than ectomycorrhizal (EM) ones.

What are the major inputs and outputs of nitrogen to terrestrial ecosystemsand how do those impact nitrogen availability over geologic time?

Nitrogen enters the living world by way of bacteria and other single-celled prokaryotes, which convert atmospheric nitrogen—N2-into biologically usable forms in a process called nitrogen fixation. Some species of nitrogen-fixing bacteria are free-living in soil or water, while others are beneficial symbionts that live inside of plants. Nitrogen is a key component of the bodies of living organisms. Nitrogen atoms are found in all proteins and DNA Nitrogen exists in the atmosphere as N2 gas. In nitrogen fixation, bacteria convert N2 into ammonia, a form of nitrogen usable by plants. When animals eat the plants, they acquire usable nitrogen compounds Nitrogen is a common limiting nutrient in nature, and agriculture. A limiting nutrient is the nutrient that's in shortest supply and limits growth. When fertilizers containing nitrogen and phosphorus are carried in runoff to lakes and rivers, they can result in blooms of algae—this is called eutrophication.

Is soil texture (percentages of sand, silt, and clay) the same thing as macroaggregates, microaggregates, and sub-microaggregates?

No soil texture is not the same thing as aggregates! Size and percentage of individual soil particles (sand, silt, clay) determine a soil's texture *So fine texture soils tend to develop soil aggregate quickly while coarse-textured soils may take longer to develop soil aggregates

What are two main advantages to using cover crops?

Opportunity to greatly increase plant (and subsequently animal and microbe) biodiversity Greater annual duration of greater vegetative resource use and function (i.e. supports health of the soil year-round)

Identify three ways that plants can be used in phytoremediation

Phytostabilization - providing plant cover to keep contaminated soil stable and in-place Enhanced rhizosphere photodegradation - certain plant species many produce root exudates that encourage bacteria to break down the pollutant in the rhizosphere Hyperaccumulation - certain plant species may take up a pollutant from the soil so it can be removed with the harvested plant

Why do bacteria produce biofilms, and what are the consequences for soil structure?

The bacterial communities that coat soil aggregates have a complex structure - they often occur as biofilms, microbial communities embedded in a matrix of polysaccharides secreted by bacteria. This microbial "slime" protects bacterial water stress by holding water like a sponge. biofilm forms when certain microorganisms (for example, some types of bacteria) adhere to the surface of some object in a moist environment and begin to reproduce. The microorganisms form an attachment to the surface of the object by secreting a slimy, glue-like substance.

The soil is a dynamic interface between what?

The biosphere (life) The hydrosphere (water) The lithosphere (rock) The atmosphere (air)

How is oxygen diffusion into soils affected by soil water?

The soil oxygen diffusion is limited by 2 resistance factors related to soil structure and texture; the first is related to the blocking effect of water, indirectly related to soil porosity, and the second is the effect of soil structural shape, directly related to soil particle size and tortuosity

In which of the four "Earth domains" do soil bacteria and microfauna exist?

They live in the rhizosphere

Water is primarily stored in soils as...

Thin films on the surfaces of soil particles

Why is decomposition so important to nitrogen and phosphorus cycling?

When these plants and animals die, decomposers like bacteria and fungi break down their organic matter, returning nitrogen to the soil. Other essential nutrients, such as phosphorus, also go through similar biogeochemical processes. Weathering and mining release phosphorus from rock in the form of phosphates, which are released into the soil. Phosphates are then consumed by plants and algae and these organisms are eaten by animals. When the animals die, their remains decompose and phosphates are returned to the soil. Decomposers play a crucial role in the Nitrogen Cycle by breaking down dead organic matter and releasing nutrients back into the soil. The nitrogen in the dead organic matter is converted into a form that can be taken up by plants, which helps to regulate the amount of nitrogen available in the environment. Phosphorus can be transferred to other organisms when they consume the plants and algae. Animals either release phosphorus through urination or defecation, when they die and are broken down by bacteria. The organic phosphorus is released and converted back into inorganic phosphorus through decomposition

What is the correct ordering of particle sizes, from smallest to largest?

clay < silt < sand

All else equal, what type of soil will have the smallest pore sizes and thus hold the most water?

clay-dominated soil

For upland plant, the main challenge of waterlogged soils is

not enough oxygen at their roots

What are the THREE most important biological processes of soil aggregation?

the enmeshment of particles by sticky networks of roots and fungal hyphae the production of organic glues by microorganisms, especially bacteria and fungi the burrowing and molding activities of soil animals

Which of the following statements about water are true

water molecules exhibit polarity: one side of the molecule is slightly positive and the other side is slightly negative the positive side of a water molecule tends to stick to negatively-charged particles (such as clay platelets) (this is called adhesion or adsorption) the negatively-charged side of a water molecule tends to stick to the positively-charged side of another water molecule (this is called cohesion)

At field capacity, the force of _____(a)_____ is counterbalanced by the force of _____(b)______

(a) gravity (b) adhesion to soil particles

Under most conditions, the concentration of _____(a)_____ is greater in the air than in the soil, whereas the concentration of _____(b)______ is greater in the soil than in the air.

(a) oxygen (b) carbon dioxide

Physical-chemical processes are more important in the formation of ______(a)______ aggregates, whereas biological processes are more important in the formation of ______(b)______ aggregates.

(a) smaller (b) larger

What does "mineralize nitrogen" mean and why is it so important?

****Nitrogen mineralization is the conversion of organically bound nitrogen in soil organic matter, crop residues, manure and other organic amendments into inorganic forms of ammonium and nitrate. Soil microbes do the conversion, which makes the process highly dependent on growing season weather. Nitrogen mineralization is an important process and vital part of soil fertility. It is the process by which organic nitrogen is converted to plant-available inorganic forms. It is regarded as a potential indicator to comprehend the soil's response to biological change Mineralization is the process by which microbes decompose organic N from manure, organic matter and crop residues to ammonium. Because it is a biological process, rates of mineralization vary with soil temperature, moisture and the amount of oxygen in the soil (aeration). Mineralization readily occurs in warm (68-95°F), well-aerated and moist soils. R-NH2 organic N → NH3 ammonia → NH4+ Ammonium

Does more water leave the land due to evapotranspiration or via rivers?

**More water leaves via evapotranspiration - shows the importance of the water cycle

By what mechanisms is soil carbon protected from further decompositionand thus able to contribute to carbon sequestration?

**The stabilization of organic matter can occur through occlusion (entrapment in aggregates) and by sticking to soil particles. Fresh residues will decompose over short time periods (days, months, years), while stabilized forms of organic matter have longer turnover times (decades).

In what ways are higher-order roots different from lower-order roots?

1st order is the finest roots analogous to leaves, they interact with the environment taking up nutrients and interacting with fungi and bacteria like a leaf is. They respire the most, they are the most active. As you go from first order through the higher order - they become more like branches and trunks which provide structure for the plant. Not as much respiration as first order roots. Functionally, lower root orders have greater absorptive capacity, respiration rate, and experience increased mycorrhizal colonization, whereas higher root orders have greater transport capacity and life spans

What are the major components of soil and what are their approximateProportions?

25% air 25% water 45% mineral particles 5% organic matter (organisms, roots, humus) Translocation involves the movement of soil-forming materials through the developing soil profile. Translocation occurs by water running through the soil transferring material from upper to lower portions. Burrowing animals like earthworms, ants, etc, move soil materials within the profile. Burrowing animals create pathways through which air & water can travel promoting soil development

Why is the concentration of carbon dioxide higher in soils than in the openAtmosphere?

Carbon dioxide is much more abundant in soil gas (the air in soil) than in the atmosphere. This is because plant roots respire and produce CO2, and because oxidative decay of organic matter produces CO2 The very high CO2 concentrations found are explained as being due to the release of CO2 during evaporation of water, the high solubility of CO2 in soil water and the high rate of microbiological activity

What are cover crops? Given everything we know about how roots and the rhizosphere influence beneficial soil processes and how a diversity of plant roots can influence soils in a greater number of ways, why are cover crops such an important component in the management of healthy soils?

Cover crops are plants that are planted to cover the soil rather than for the purpose of being harvested. Cover crops manage soil erosion, soil fertility, soil quality, water, weeds, pests, diseases, biodiversity and wildlife in an agroecosystem. Cover crops increase soil organic matter, and improve soil fertility by capturing excess nutrients after a crop is harvested. They also raise soil moisture holding capacity, help prevent soil erosion, limit nutrient runoff, reduce soil compaction, and even help suppress some pests.

What is the difference between evaporation and transpiration? And what is "evapotranspiration"?

Evaporation- Is a change from a liquid to a gas at the surface of the liquid Transpiration- Evaporation of water from the leaves of a plant "Evapotranspiration- The process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants. evapotranspiration is the sum of all processes by which water moves from the land surface to the atmosphere via evaporation and transpiration.

Although there are many pathways, degradation of organic chemicals in the soil (such as pesticides) can only occur through the actions of soil organisms

False

Because of the massive scale of modern agriculture, we are the first civilization that has had to deal with soil erosion and its control (analogous to the way we are the first civilization that has had to deal with greenhouse gas emissions, plastic pollution, etc.)

False

Because of their large pore sizes, sandy soils retain more water than clay soils.

False

Despite the variety of possible feedstocks and pyrolysis temperatures used, one of the great benefits of using biochar is the uniform chemical properties of the final product

False

In a given habitat, the taxonomic diversity of plants is typically much greater than the taxonomic diversity of soil flora and fauna.

False

In the old days, on integrated farms (i.e. farms with crops, pastures, and animals) manure was a nuisance that had to be dealt with that did not benefit the soil or the farm. Today, with CAFOs, manure is an excellent opportunity to recycle nutrients at nearby farms.

False

More water leaves terrestrial ecosystems via lakes, rivers, and groundwater than via surface evaporation and transpiration

False

What two taxa of organisms are together responsible for ~95% of total decomposer biomass and respiration?

Fungi and bacteria

Microbial processes such as decomposition and nitrogen mineralization typically ________________ with increasing temperature

Increase

"Anaerobic" soils (or areas within soils or even within soil aggregates) are depleted of oxygen

True

Compared with the surfaces of micropores, the surfaces of macropores are hot spots of biological activity, including the secretion of exudates by roots, rapid growth and turnover of bacterial biofilms, and predation by soil animals

True

Does "healthy" soil have a diversity or uniformity of pore sizes? Why does that diversity or uniformity make it "healthy"?

*An ideal soil for plant growth contains 50% pore space and 50% solids, with the pore space filled with equal parts air and water. This distribution rarely occurs because pore space varies with soil texture and management. Healthy soil contains aggregates that help it bind together, preventing erosion and run-off. It can hold more water, so plants fare better in drought. It contains more bacteria & fungi that help plants fight diseases and pests. And healthy soil also contains more minerals and nutrients that feed plants.

What four huge Earth domains come together in soil? Importantly, in whatHow are each domain present and incorporated in soil?

-Carbon is essential to each of the earth's spheres and is found in all 4 domains -Lithosphere (rocks) The solid, rocky shell of the earth is the lithosphere & is present as the mineral material composing the soil -Hydrosphere (water) It is there as moisture in the soil -Atmosphere (air) It is also there as air pockets between the pieces of soil -Biosphere (living things) It Is represent as insects crawling through the soil or plants growing in the soi

The surfaces of most clays are _____(1)_____ charged. Thus, _____(2)_____ charged nutrient ions can electrostatically 'stick' to them

1. negatively 2. Positively

**What is the "soil-plant-atmosphere continuum"? How does it work? What are the consequences of xylem cavitation (i.e. when the continuous column of water breaks inside a plant's xylem)?

According to this concept (Soil, plant, animals, and surrounding atmosphere), into a dynamic system in which the various transport processes involving energy and matter occur simultaneously Xylem cavitation occurs when air is pulled across interfaces between xylem water and air resident in the plant body. This process leads to air blockages in the xylem that cuts the plant off from its water supply in the soil. A large body of evidence clearly demonstrates the vulnerability of stems, roots, and leaves to this cavitation processes and the detrimental impact it has on plant productivity and survival **In class notes: Column of water in the xylem - if it is broken then it is like the plant is drinking out of a broken straw. If you forget to water house plants, there are going to be lots of plants that end up and die and it is due to xylem cavitation.

At what scale are biological processes most important for aggregation? What are those biological processes? Why does each one exist (from the organism's "perspective") and how does it contribute to aggregation?

Activities of Soil Organisms- among the biological processes of aggregation, the most prominent are: 1) the burrowing & molding activities of soil animals, 2) the enmeshment of particles by sticky networks of roots & fungal hyphae, and 3) the production of organic glues by microorganisms, especially bacteria & fungi.

Why do water molecules adhere to charged surfaces and cohere to each other?

Adhesion: The ability of a substance to stick to an unlike substance; attraction between unlike molecules For example, Adhesion is observed when water "climbs" up the tube placed in a glass of water. This is because the water molecules are attracted to the charged glass wall of the capillary more than they are to each other and therefore adhere to it. This type of adhesion is called Capillary action Cohesion: Various intermolecular forces that hold solids and liquids together; attraction between molecules. Water molecules are bent so the hydrogen atoms are to one side of the oxygen atom and when it comes to molecules opposite attract - a bond forms between the negative side of one water molecule and the positive side of another.

What is the *most likely* fate of a molecule of nitrogen in a decomposing leaf on the forest floor?

After processing by bacteria or fungi, it will be taken up by a plant in that same area

Soil animals mainly influence decomposition by... (select three)

Altering soil structure Fragmenting, transforming, and transporting litter Grazing populations of bacteria & fungi

What is manure and in what contexts can the carbon, microbes, and (most importantly!) nutrients that manure contains be returned to the soil? And in what contexts is that return cost-prohibitive?

Animal manure is considered an agricultural commodity that can be utilized as a fertilizer source for pastureland, cropland and hay production. Manure is recognized as an excellent source of the plant nutrients nitrogen (N), phosphorus (P) and potassium (K). Manure is the decomposed form of dead plants and animals, which is applied to the soil to increase production. It is a natural form of fertilizer and is cost-effective. The human and animal excreta is also used as manure. The livestock manure is rich in nitrogen, phosphorus, and potassium. While some livestock producers haul liquid manure in tankers, it is usually considered cost prohibitive. The amount of water is so great that the hours spent distributing it and the resulting dollar cost exceeds the value of the manure supplied nutrients when using tankers

Dormancy in bacteria: why and to what extent?

Because most bacteria are immobile, a bacterial colony eventually exhausts the substrates in its immediate environment, especially within soil aggregates that have restricted water movement. When this occurs they become inactive & reduce their respiration to negligible rates. About 50-80% of the bacteria in soils are metabolically inactive. Inactive bacteria activate in the presence of labile substrates, for example when a root grows through the soil & exudes carbohydrates.

Does soil pH affect nutrient availability for plants? If so, what is the "sweetSpot"?

Between about 6 and 8, the majority of nutrients can be easily taken up in this range of pH. So around a neutral pH More H+ in soil means it is acidic and the more OH- in soil the more alkaline/basic It has been determined that most plant nutrients are optimally available to plants within this 6.5 to 7.5 pH range, plus this range of pH is generally very compatible with plant root growth. Ultimately, the pH of your nutrient solution and root zone affects your plants' ability to get the nutrients they need. Try to aim for what is known as the 'sweet spot' for your chosen growing method. For hydroponics, your nutrient solution should be within the 5.8-6.5 pH range.

What is biochar, and what contributes to the huge diversity of properties of finished biochar? Why is biochar potentially useful as a soil amendment?

Biochar is black carbon produced from biomass sources (i.e. wood chips, plant residues, manure or other agricultural waste products) for the purpose of transforming the biomass carbon into a more stable form (carbon sequestration) Applications of biochar in soil are known to have a significant impact on various properties of soil. The higher porosity of biochar tends to improve a wide range of soil physical properties such as total porosity, soil density, soil moisture content, water holding capacity, and hydraulic conductivity - being used as soil amendment have a significant effect on soil fertility by altering the chemical, biological, and physical characteristics of the soil

What observations about indigenous soil management practices in the very poor soils of the Amazon led to the current "biochar fever"?

Biochar is the solid material obtained from the carbonization of biomass, or simply, charcoal produced by the burning of wood and plant matter at low oxygen levels. Research being performed by Cornell University, the University of Oxford, and others has helped to bring further understanding of biochar and its use in the Amazon. By incorporating biochar in conjunction with nutrient additions, the early indigenous peoples of the Amazon converted extremely poor soils into highly fertile and productive land. The practice has been dated back to the pre-Columbian Indians from 500 to 2500 B.C. in the Brazilian Amazon. Today, it is seen as an important tool for increased food security and even to combat climate change. Contrary to popular belief, the soils of the Amazon jungle are very poor at supporting agriculture due to their high acidic nature and low nutrient content. The humid, tropical climate has led to highly weathered soils and loss of nutrients by leaching. But the addition of biochar into these soils has been shown to increase crop yields several times. Biochar is able to buffer the acidic soils, making it a desirable alternative to conventional liming applications, which can be very expensive. Biochar also improves the efficiency of fertilizers added to the soil because it increases retention and reduces leaching. Highly stable, biochar can persist in the soil for hundreds of years.

What are the "biosolids" created by waste water treatment plants and how can they be used to improve degraded soils?

Biosolids are a good source of organic matter and nutrients and are, thus, valuable resources. They can be applied to land either to condition the soil or to fertilize crops and other vegetation. Biosolids are a product of the wastewater treatment process. During wastewater treatment the liquids are separated from the solids. Those solids are then treated physically and chemically to produce a semisolid, nutrient-rich product known as biosolids Biosolids are a beneficial resource, containing essential plant nutrients and organic matter and are recycled as a fertilizer and soil amendment. Biosolids are created through the treatment of domestic wastewater generated from sewage treatment facilities.

Explain the ways each of the components of CLORPT (climate, organisms,relief, parent material, and time) can influence soil development.

Climate: Climate describes the weather characteristics over a long period of time, including temperatures and rainfall. Soils that formed with 35 inches of rain per year are much different from soils that formed in a desert climate with only 6 inches of rain per year. Organisms: Organisms are the kinds of plants and animals that influence the way soils are formed. For example, many years of falling pine needles can make a soil slightly acidic (low pH). Similarly, earthworms have long been associated with healthy, productive soils Relief (topography) Relief describes the shape of the earth's surface, such as mountains, hills, and plains. Have you ever noticed how soils in low-lying areas are wetter than soils on ridges? Soils on north-facing slopes tend to be cooler because the sun doesn't shine on them as much as on south-facing slopes. That's the 'topography factor" in action Parent material Parent material describes the kind of rocks or transported sediments that the soil formed in. Examples include alluvial, colluviums, eolian, glacial, residual, and organic soils Time: Older soils usually have more differences in color, structure, and texture as you go down from the soil surface. Reddish colors might be caused by iron oxides and certain kinds of clay that haven been washed down and concentrated at a lower level (soil horizon). Younger soils such as a big deposit of windblown dune sand or floodplain might have similar characteristics through the soil profile

One would expect very little correlation between rates of decomposition and rates of nitrogen cycling

False

Oxygen diffuses much more easily through water than through air

False

The hierarchical organization of aggregates (where larger aggregates form from smaller aggregates... which form from even smaller bits of clay, silt, and humus) is important but only occurs in a few rare soil types

False

Thermophilic composting requires conditions for anaerobic (not aerobic) decomposition

False

insofar as they supply carbon to the soil system, dead roots and root exudates are not nearly as important as leaf litter

False

Once inside an ecosystem, what is the most common "circuit" that anitrogen or phosphorus atom will travel?

Five main processes cycle nitrogen through the biosphere, atmosphere, and geosphere: nitrogen fixation, nitrogen uptake through organismal growth, nitrogen mineralization through decay, nitrification, and denitrification. Microorganisms, particularly bacteria, play major roles in all of the principal nitrogen transformations. Because these processes are microbially mediated, or controlled by microorganisms, these nitrogen transformations tend to occur faster than geological processes like plate motion, a very slow, purely physical process that is a part of the carbon cycle. Instead, rates are affected by environmental factors that influence microbial activity, such as temperature, moisture, and resource availability. Phosphate compounds in the soil can be taken up by plants and, from there, transferred to animals that eat the plants. When plants and animals excrete wastes or die, phosphates may be taken up by detritivores or returned to the soil. Phosphorus-containing compounds may also be carried in surface runoff to rivers, lakes, and oceans, where they are taken up by aquatic organisms.

What taxa of soil organisms are responsible for ~95% of terrestrialdecomposition? What ecological advantages or disadvantages does each taxa have (i.e. under what circumstances would you expect one or the other to be favored or not favored?)

Fungi and bacteria are the main initial decomposers of terrestrial dead plant material, accounting for about 95% of the total decomposer biomass and respiration. *Specifically Microflora are responsible for 95% of actual decomposition *Fungi have enzyme systems capable of breaking down all classes of plant compounds. They have a competitive advantage over many bacteria in decomposing tissues with low nutrient concentrations because of their ability to import nitrogen & phosphorus. In addition fungi typically require less nitrogen per unit biomass than bacteria, bacteria cannot move around while fungi can (slow and steady) *Bacteria can exist in a wide range of environments & bacteria can be dormant, and bacteria is way faster than fungi if environment is good (Slow and can't move but when the environment is good- it moves very fast!)

Which of the following are beneficial functions of mucigel?

Helps to stabilize soil aggregates Lubricates the soil in advance of the root tip Improves root-soil contact (important for water and nutrient uptake) Agar-like properties provide an ideal environment for soil microorganisms

What are the four USDA soil orders we have been using in all of our in-class analyses and what are their general characteristics and the contexts in which they tend to form? (No need to memorize details beyond the summary figure that looks like a sideways tree with slightly-developed Entisols on the left all the way to strongly-developed Oxisols on the right. No need to memorize the other eight USDA soil orders that we have not been using in class.)

Histosols Dark soil, high in carbon, and wet Lot of organic materials Spodosols Super acidic, cool, wet, sandy Alfisols Most, mildly aid Clay accumulation Mollisols Semiarid to moist, grassland, mollic epipedon

Root *growth* tends to __________ soil aggregation. (Note this is NOT asking about root exudates, which we already know tend to increase aggregation)

Increase

What is the main difference between the soil organic matter categories "labile carbon" and "soil humus"?

Labile carbon is rapidly decomposed (months to years), whereas soil humus is protected and thus slowly decomposed (centuries to millennia)

Identify THREE processes that may degrade organic chemicals in the soil (you don't have to explain these, just identify them)

Leaching, mineralization, communition

At what scale are physical-chemical processes most important for aggregation? What is flocculation? How does shrinking and swelling contribute to aggregation?

Most important among the physical chemical processes are: 1) flocculation, the mutual attraction among clay & organic molecules; and 2) the swelling & shrinking of clay masses **Clay platelets are negatively charged and it will stick to positively charged cations. You do not want them to repel each other if they are not very positive, but if it is very positively charged then it will stick together and this is flocculation As a soil dries out & water is withdrawn, the platelets in clay domains move closer together, causing the domains and, hence, the soil mass to shrink in volume. As a soil mass shrinks, cracks will open up along zones of weakness. Over the course of many cycles (as occurs between rain or irrigation events in the field) the network of cracks becomes better defined. In one of many ways in which physical & biological soil processes interact, plant water uptake dries the root zone & accentuates the physical aggregation processes associated with wetting & drying. Freezing & thawing cycles have a similar effect, since the formation of ice crystals is a drying process that also draws water out of clay domains. The swelling & shrinking actions that accompany freeze-thaw & wet-dry cycles in soils create fissures & pressures that alternately break apart large soil masses & compress soil particles into defined structural peds. The aggregating effects of these water & temperature cycles are most pronounced in soils with high content of swelling-type clays. Especially vertisols, mollisols, and some alfisols.

Why is soil organic matter so important to soil aggregation?

Organic matter plays a significant role in crop production and soil health by improving physical, chemical, and biological functions in the soil. Increasing levels of organic matter aid in soil structure, water-holding capacity, nutrient mineralization, biological activity, and water and air infiltration rates

Most nitrogen molecules in the soil exist in what state?

Organic, bound up in litter (aka "particulate organic nitrogen" or "dead organic matter")

In what ways is oxygen availability heterogeneous in soils?

Oxygen transport in soils occurs mainly by diffusion, a process that depends upon physical characteristics of the soil such as texture, structure, porosity, and water content.

What are the major inputs and outputs of phosphorus to terrestrialecosystems and how do those impact phosphorus availability over geologic time?

Phosphorus is an essential nutrient found in the macromolecules of humans and other organisms, including DNA The phosphorus cycle is slow. Most phosphorus in nature exists in the form of phosphate ion— PO 3-4 Phosphorus is often the limiting nutrient, or nutrient that is most scarce and thus limits growth, in aquatic ecosystems.When nitrogen and phosphorus from fertilizer are carried in runoff to lakes and oceans, they can cause eutrophication, the overgrowth of algae. The algae may deplete oxygen from the water and create a dead zone. Phosphate compounds in the soil can be taken up by plants and, from there, transferred to animals that eat the plants. When plants and animals excrete wastes or die, phosphates may be taken up by detritivores or returned to the soil. Phosphorus-containing compounds may also be carried in surface runoff to rivers, lakes, and oceans, where they are taken up by aquatic organisms.

Once inside an ecosystem, in what state does the typical nitrogen orphosphorus atom spend most of its time?

Phosphorus is most commonly found in rock/soil formations and ocean sediments as phosphate salts. Phosphate salts that are released from rocks through weathering usually dissolve in soil water and will be absorbed by plants. Nitrogen moves slowly through the cycle and is stored in reservoirs such as the atmosphere, living organisms, soils, and oceans along its way. Most of the nitrogen on Earth is in the atmosphere. Approximately 80% of the molecules in Earth's atmosphere are made of two nitrogen atoms bonded together (N2).

Although the huge diversity of chemical pollutants and the huge diversity of soils precludes general statements about the ways that chemical pollutants interact with soils, you should understand the possibilities for intact organic pollutant movement to, within, and out of soils, along with the various processes that might degrade an organic pollutant in soils.

Phytoremediation is a general term for several ways in which plants are used to remediate sites by removing pollutants from soil and water. Plants can degrade organic pollutants or contain and stabilize metal contaminants by acting as filters or traps. In many cases, plants have the ability to metabolize organic pollutants by transformation and conjugation reactions followed by compartmentalizing products in their tissues.

What is phytoremediation, and what are three ways that phytoremediation can be used to stabilize and/or improve polluted soils?

Phytoremediation uses plants to clean up soil, air, and water contaminated. Three ways that phytoremediation can be used to stabilize and improve polluted soils There are a number of phytoremediation strategies that are applicable for the remediation of heavy metal-contaminated soils, including (i) phytostabilization—using plants to reduce heavy metal bioavailability in soil, (ii) phytoextraction—using plants to extract and remove heavy metals from soil, (iii) phytovolatilization—using plants to absorb heavy metal from soil and release into the atmosphere as volatile compounds, and (iv) phytofiltration—using hydroponically cultured plants to absorb or adsorb heavy metal ions from groundwater and aqueous waste Phytostabilization - providing plant cover to keep contaminated soil stable and in-place Enhanced rhizosphere photodegradation - certain plant species many produce root exudates that encourage bacteria to break down the pollutant in the rhizosphere Hyperaccumulation - certain plant species may take up a pollutant from the soil so it can be removed with the harvested plant

In what ways do roots add carbon to the soil?

Plant roots provide soil organic carbon primarily in the form of root litter and the release of organic material, including exudates, dead cells, and mycorrhizal biomass. Roots can also contribute to organic carbon input by forming soil aggregates and protecting organic carbon from the act of microbial decomposition In general plant roots control and influence soil organic carbon (SOC) dynamics by providing organic C to the soil primarily in the forms of root litter and rhizodeposition (Box 1). This C input results in SOC gain, particularly when plant roots promote SOC stabilization (Box 1).

Identify two common ways that humans affect soil structure

Plowing Compaction

Select THREE probable benefits of using biochar as a soil amendment

Remediation of organic pollutants Greater plant growth Long-term carbon sequestration

through which air & water can travel promoting soil development What are the three soil mineral particle sizes? How do their sizes influencesoil surface area, pore sizes, and water holding capacity? Apart from their sizes, what is different about them (e.g. surface charge, primary vs. secondary minerals) and what are the consequences of those differences?

Sand (0.05-2) Fast draining soils & dries easily, low nutrient storage capacity, high air space, and low primary production) Generally primary minerals that have not undergone much weather Large in size, large space, gritty, rough, or coarse, non-sticky, good drainage ability, poor water holding capacity Silt (0.002-0.05) Medium to high water retention & availability, medium nutrient storage, medium air space, and primary minerals Medium in size, medium in space, smooth and slipping, floury, non-sticky, medium drainage ability, medium water holding capacity Clay (<0.002) Sticky & easily waterlogged, high nutrient storage capacity, low air space, medium/low primary production Secondary products of the weathering of primary minerals-as weathering continues, the soil particles break down and become smaller and smaller Very fine in size, small spaces between particles, sticky when wet, hard when dry, it swells and shrinks, absorbs water, poor drainage, good water holding capacity

identify the TWO principle outputs of a modern wastewater treatment plant

Sludge Effluent

Smaller soil particles are glued together by such things as organic matter, iron oxides, polyvalent cations, polysaccharide secreted by roots and bacteria, fungal hyphae, etc. to form what?

Soil aggregates

What are the three ways that soil erosion typically occurs, and what human activity is directly or indirectly linked to almost all soil erosion? In the context of human civilization, is soil erosion a new problem or an old problem?

Soil erosion typically occurs when dirt is left exposed to strong winds, hard rains, and flowing water - and also human activities like tilling and farming because many of these practices disturb and degrade the ground and over long periods of time that damages the soil quality The problems of soil erosion seems to have affect those civilizations that had developed advanced methods of agriculture coupled with rampant deforestation - around 4000 years ago, human activities had already significantly accelerated soil erosion around lake beds on a global scale

What were the key takeaways from the "Kiss the Ground" documentary and how do they connect with class concepts?

Soil in the context of climate change, carbon!! Soils can store carbon, if we use regenerative agriculture and less agriculture - we can help the atmosphere and prevent desertification. Call to re-envision our agricultural system

What is the physical and ecological significance of soil pore space? What is ecologically significant about macropores?

Soil porosity provides space for microbial growth and improves the aeration of the soil, nutrient availability, and water drainage and retention capacity Soil pores exist between and within aggregates and are occupied by water and air. Macropores are large soil pores, usually between aggregates, that are generally greater than 0.08mm in diameter. Macropores drain freely by gravity and allow easy movement of water & water. They provide habitat for soil organisms and plant roots can grow into them. With diameters less than 0.08mm, micropores are small soil pores usually found within structural aggregates. Suction is required to remove water from micropores.

What observations did we make on the spodosol soil monoliths in week 1?

Soil profile (O,A,E,B,C,R) -O (Humus or organic): Mostly organic matter such as decomposing leaves. The O horizon is thin in some soils, thick in others, and not present at all in others -A (topsoil): Mostly minerals from parent material with organic matter incorporated. A good material for plants and other organisms to live in -E (eluviated): Leached of clay, minerals, and organic matter, leaving a concentration of sand and silt particles of quartz or other resistant materials - missing in some soils but often found in older soils and forest soils -B (subsoil): Rich in minerals that leached (moved down) from the A or E horizons and accumulated here -C (parent material): The deposit at Earth's surface from which the soil developed -R (bedrock): A mass of rock such as grantile, basalt, quartzite, limestone or sandstone that forms the parent materials for some soils - if the bedrock is close enough to the surface to weather. This is not soil and is located under the C horizon. -In class discussion -Ups and downs & horizons -Sand -Litter (roots) & at all stages of decomposition Fungi (organism) & mycelium (body) & hyphae (which make up the mycelium) Ants and other insects Burnt bits of wood (charcoal) Living plants

What are the general soil horizons O, A, B, C, & R, and what are their basic characteristics?

Soil profile (O,A,E,B,C,R) O (Humus or organic): Mostly organic matter such as decomposing leaves. The O horizon is thin in some soils, thick in others, and not present at all in others. Organic surface layer: plant litter layer- the upper part is often relatively undecomposed but the power part may be strongly humified. A (topsoil): Mostly minerals from parent material with organic matter incorporated. A good material for plants and other organisms to live. Surface soil, layer of mineral soil with most organic matter accumulation and soil life. E (eluviated): Leached of clay, minerals, and organic matter, leaving a concentration of sand and silt particles of quartz or other resistant materials - missing in some soils but often found in older soils and forest soils B (subsoil): Rich in minerals that leached (moved down) from the A or E horizons and accumulated here. Less organic matter here than A horizon. C (parent material): The deposit at Earth's surface from which the soil developed R (bedrock): A mass of rock such as grantile, basalt, quartzite, limestone or sandstone that forms the parent materials for some soils - if the bedrock is close enough to the surface to weather. This is not soil and is located under the C horizon.

Soil texture affects (select all that are correct)

Soil surface charge Soil surface area Soil water holding capacity Soil aeration (ability to be infiltrated by air)

How does temperature affect soil processes?

Soil temperatures strongly influences biological processes such as seed germination, seedling emergence and growth, root development and microbial activity Temperature and moisture influence the speed of chemical reactions, which in turn help control how fast rocks, weather and dead organisms decompose. Soils develop faster in warm, moist climates and slowest in cold or arid ones.

What is the "hierarchy of aggregation"?

Surface horizons are usually characterized by roundish granular structure that exhibits a hierarchy in which relatively large macroaggregates (0.25-5mm in diameter) are comprised of smaller microaggregates (2-250um) The hierarchical organization of aggregates seems to be characteristic of most soils, with the exception of certain Oxisols & some very young Entisols. Small particles of organic matter are often occluded inside the macro- & microaggregates. At each level in the hierarchy of aggregates, different factors are responsible for binding together the subunis. *Primary particles → Submicroaggregates → Microaggregates → Macroaggregate

In thermophilic composting, what does the brown hump shaped line represent?

Temperature (deg c)

What are the approximate C:N ratios of plants, soil organic matter, and soilbiota, and under what conditions will soil biota tend to mineralize nitrogen?Are those conditions common or rare?

The C:N ratio is a quick way to evaluate the balance between two elements present in the soil that are both essential for crop growth and microbial health. The C:N ratio in the organic matter of agricultural soils ideally averages about 10:1. This is considered an indication of a dynamic equilibrium condition that can and should be maintained.

What are the main causes of soil erosion?

The action of wind on dry, exposed soil The effects of gravity on conventional tillage practices (soil gradually moves downslope) The action of water washing soil away

From the standpoint of limitation by carbon, nitrogen, and phosphorus andits effect on nutrient cycling, are large animals (e.g. humans, cows, bison)similar to soil microbes or very different from soil microbes?

The answer is very similar, soil organisms are 10 carbon: 1 nitrogen We like the soil organisms, contain a lot of carbon and nitrogen as do all other organisms

Which of the following are true statements about transpiration?

The low water potential of unsaturated air outside leaves, relative to the water potential of saturated air inside leaves, is the major driving force for water loss from leaves Water lost from leaves drives water transport up the stem Water transport up the stem drives water uptake into roots As soils dry out, transpiration requires water molecules to travel ever-greater distances in the soil because water cannot travel directly across air-filled pores

Explain the relationship between evapotranspiration, gravity, and matricforces on soil water. How are these related to "field capacity" and the"permanent wilting point"?

The permanent wilting point is the point when there is no water available to the plant. Field capacity is the water remaining in a soil after it has been thoroughly saturated and allowed to drain freely, usually for one to two days. Permanent wilting point is the moisture content of a soil at which plants wilt and fail to recover when supplied with sufficient moisture. Water storage and redistribution are a function of soil pore space and pore-size distribution. Generally speaking, clay-rich soils have the largest pore space, hence the greatest total water holding capacity. However, total water holding capacity does not describe how much water is available to plants, or how freely water drains in soil. These processes are governed by potential energy. Water is stored and redistributed within soil in response to differences in potential energy.

Why is the rhizosphere a special place, ecologically?

The rhizosphere is a narrow zone of soil surrounding and influenced by the root of vascular plants. This zone is characterized by intense biological activity owing to the release of root exudates, which stimulate or inhibit rhizosphere organisms. Important microbial processes that are expected to occur in the rhizosphere include pathogenesis and its counterpart, plant protection/growth promotion, as well as the production of antibiotics, geochemical cycling of minerals and plant colonization *Hotspots of biological activity!

What are the major classes of organic material present in soils? Which areprimarily "labile carbon" and which are primarily "soil humus" and what are the important distinctions between these two categories?

The term soil organic matter encompasses all the organic components of a soil: 1) living biomass (intact plant & animal tissues & microorganisms); 2) plant litter or residues-bits of dead roots & other plant residues in various stages of decay & of various sizes; 3) dissolved organic biomolecules ranging widely from plant amino acids to microbial enzymes; and 4) a complex mixture of biomolecule on particle surfaces, tiny of no longer identifiable tissue occluded inside microaggregates, and bits of plant material that have been charred by fire. We will refer to the various components in this fourth broad category of organic material as Soil Humus The first three categories referred to as the labile carbon pool (or group)

What is thermophilic composting? What makes finished compost a useful soil amendment?

Thermophilic composting is a composting method that utilizes heat-loving bacteria and fungi to generate high temperatures, which helps kill pathogens and weed seeds in the compost pile. It is the result of microbial decomposition of dead organic matter in the presence of oxygen (aerobe conditions). Thermophilic compost, also known as hot rotting compost or windrow compost, is the most common compost, which is produced in medium to large quantities worldwide

In terms of local recycling, are the nitrogen and phosphorus cycles similaror very different?

These form their respective biogeochemical cycles that show the movement of nitrogen and phosphorus through the lithosphere, hydrosphere and biosphere. However, the atmosphere does not play a major role in the movement of phosphorus. Of the two, nitrogen is recycled whereas phosphorus is not. They are similar but, Nitrogen is recycled whereas phosphorus is not

Although exceptions exist, what are the main ecological roles of soilmicrofauna, mesofauna, and macrofauna? What are their (mainly indirect,but still super important) effects on decomposition?

They are predators of bacteria, fungi, and other protozoa Microfauna (body size <0.1mm) Microfauna are the smallest animal (<0.2 mm diameter) they include nematodes, protozoans, such as ciliates and amoebae, and rotifers Protozoans are single-celled animals that ingest their prey primarily by phagocytosis, that is, by enclosing them in a membrane-bound structure within the cell ***Microflora is are responsible for 95% of actual decomposition Mesofauna (up to 2mm) The Mesofauna are a numerically abundant & taxonomically diverse group of soil animals 0.1-2 mm in diameter. These are the animals with the greatest effect on decomposition. They fragment & ingest litter coated w/microbial biomass, producing large amounts of fecal material w/a greater surface area and moisture-holding capacity than the original litter. This altered litter environment is more favorable for decomposition. Macrofauna (up to 20mm) Large soil animals (macrofauna) such as earthworms & termites, are ecosystem engineers that alter resource availability by modifying the physical properties of soil & litter Some of them, like the mesofauna, fragment litter. Others burrow or ingest soil, reducing soil bulk density, breaking up soil aggregates, and increasing soil aeration & water infiltration.

In what ways does tillage (i.e. plowing) directly influence a farm's soilaggregation and soil organic matter (and thus also indirectly influence soil aggregation)?

Tillage can both promote and destroy aggregation. If the soil is not too wet or too dry, tillage can break large clods into natural aggregates, creating a temporarily lose, porous condition conducive to the easy growth of young roots and the emergence of tender seedlings. Tillage can also incorporate organic amendments into the soil and kill weeds Over long periods tillage greatly hastens the oxidative loss of soil organic matter, thus weakening soil aggregates. Tillage operations, especially if carried out when the soil is wet, also tend to crush or smear soil aggregates, resulting in loss of macroporosity and the creation of a puddled condition.

What are the four processes that - together with gravity and the inescapable up/down nature of soil - lead to soil horizons?

Transformations: Physico Chemical & biological modifications of soil parent materials Oxidation/reduction for minerals Microbe decomposition for organic matter Translocation: Movement of material within a horizon or vertically from one horizon up or down to another Water penetrating or percolating down with gravity or rising up by capillary action Additions: Inputs of materials to the soil profile from outside sources Inputs of organic matter from fallen plant leaves Losses: Grazing by animals or people

Although the *absolute* amount of nutrients in a compost heap cannot increase, the *concentration* The nutrients in a compost heap increases over time as more labile carbon is decomposed.

True

Although their inputs and outputs from ecosystems are quite different, the internal recycling of phosphorus is similar to the internal recycling of nitrogen

True

The *vast* majority of livestock in the United States are raised in concentrated animal feeding operations (CAFOs)

True

The two main competitive advantages fungi have over bacteria are (1) that fungi can move carbon, nitrogen, and phosphorus from areas of high availability to low availability via hyphal networks and (2) fungi have slightly less need for nitrogen (i.e a higher C:N ratio)

True

Most soil is 50% soil and 50% pore space, what typically occupies the pore space?

Water Air Biota

identify TWO processes that may transfer (but not degrade) organic chemicals within the soil or out of the soil

Water transport, Diffusion, bioturbation

What does it mean to say an organism (e.g. plants, soil microbes) is "carbon limited" or "nitrogen limited" or "phosphorus limited"?

When carbon, nitrogen, or phosphorus become limiting in the environment, this can be reflected in a lower level of nutrient present in the algal cell. For example, if P concentration becomes growth-limiting in a stream, tissue C:P. and N:P

What is true of most soil bacteria? (select one)

When conditions are poor, they can remain dormant for long periods of time

What are the causes and consequences of soil compaction?

When soil aggregates or particles are pressed together constantly over time, soil compaction takes place. Soil compaction and its resulting issue must be considered when planting new crops, building roadways, or during restoration. Soil compaction also comprises soil strength. When the soil is dense and of low porosity, roots have a harder time digging down through compacted layers to take hold Soil compaction is most often seen when machinery or automobiles pass over the surface, or animals/humans. Soil types also have an influence on compaction depending on their moisture levels

Relative to the soil horizons and the "drip line" (i.e. the edge of a plant's canopy), how do real root systems tend to grow?

Where the line of the plants vegetation The root system does NOT mirror the drip line below the ground, it extends way past the drip line A tree's root system is typically fairly shallow (frequently no deeper than 2m), but is wide spreading, with the majority of roots found in the upper 60cm in soil