What are the 6 key functions of soils in ecosystems?
a medium for plant growth, determines the fate of water, nature's recycling system, provides habitat for living organisms, influence the atmosphere, a medium for building
How does the pedosphere interact with the lithosphere?
The minerals present in soil are also the minerals that reach further down to make up the lithosphere
How does the pedosphere interact with the hydrosphere?
Water travels through the soil or flows over its surface therefore any pollution in the pedosphere ends up in the hydrosphere, soil channels rain water to rivers
How does the pedosphere interact with the atmosphere?
Soil releases gases into the atmosphere such as carbon dioxide, oxygen, and nitrogen and removes gases
How does the pedosphere interact with the biosphere?
Soil affects the biosphere by decomposing organic matter and biomass from plants animals and microbes and allowing it to be reused in the life cycle
surface horizon with lots of organic material
horizon nearest the surface, has lots of mineral particles but is darker due to organic matter
the bleacher horizon where things are being leached out
underlying layers that have accumulated materials washed down from above or formed from weathering with little organic matter
the least weathered soils horizon
organically enriched, majority of plant roots found here
where most water is stored, roots can't really grow here, it's hard to modify subsoil
Minerals make up what persent of the soil and what are their purpose?
Minerals make up 45% of the soil (loam soil good for growing plants), sand silt and clay are the main particles, they are essential for plant growth
Air makes up what percent of the soil and what is its purpose?
Air makes up 20-30%, air content is related to water content, the composition of soil air varies from place to place and soil air has a higher moisture content. The content of CO2 is usually high and O2 lower
Organic matter makes up what percent of the soil and what is its purpose?
Organic matter makes up 5%, made up of biomass, remains of organisms, and organic compounds. A continues cycle of matter being gained from residues or death of plants and animals, and lost by releasing of CO2
Water makes up what percent of soil and what is its purpose?
Water makes up 20-30%, water is held in pores so it can’t flow like we think of water flowing, it’s never pure it contains dissolved substances so is more accurately called a solution than water
What is root interception?
It is when roots continually grow into new, undepleted soil.
What is diffusion?
It is when nutrient ions continually move from areas of greater concentation toward the nutrient-depleted areas of lower concentration around the root surface.
What is mass flow?
When dissolved nutrients are carried along with the flowing soil water toward a root that is actively drawing water from the soil.
Diagram the ways soil provides nutrients to growing plant roots
List five ways that human activity can diminish soil quality
mismanagement of forests, farms, and rangeland. Accumulation of salts due to improper irrigation. Cultivating without returning organic residues. Contamination from chemical spills nd industrial processes
What is Hydrolysis?
adding water across a bond
What is hydration?
adding water to a chemical structure
What is carbonation?
Co2 dissolving in water
What is dissolution?
minerals dissolving in water
What is oxidation-reduction?
loss and gain of electrons (moving from Fe2 to Fe3)
What is complexation?
It's the equation that looks really complex, it is mediated by soil biological processes
What is physical weathering?
disintegration caused by temeprature, water, wind, ice, and organisms. The minerals and textures partly determine the rate it is weathered.
What is chemical weathering?
Chemical weathering is the chemical composition of the rock is altered.
Five soil forming factors?
climate, biota, parent materials, topography, time
describe the relationships between residual, transported and organic parent materials
Residual materials are formed in place, organic form in wet places where plant growth exceeds the rate of decomposition (commonly referred to as peat), and transported materials are materials that move places due to various factors.
How does temperature and rainfall influence soil formation?
The greater the depth of water penetration, the greater the depth of weathering soil and development. Salts can build up in areas that do not receive enough rainfall and can kill plants. For every 10 C raise in temp, the rates of biochemical reactions more than double. Weathering is maximized in areas with warm temperatures and abundant water.
How do plants and animals influence soil formation?
vegetative over reduces natural soil erosion rates, organic acids produced from some plants bring iron and aluminum into the soil, the nutrient cycling of trees greatly affects the soil acidity, earthworms and the like effectively mix the soils to make the nutrients better distributed-pedoturbation
Describe the four basic processes of soil formation
Redistribution/Translocation: Eluviation, exit, Illuviation, into, Additions (dust carried by the wind, plant materials), Transformations (decomposition, chemical and physical weathering), and Loss of materials (leaching, erosion)
Relate the four basic processes of soil formation to a hypothetical tall grass prairie soil
When plants get established they begin to provide additions of litter and root residues on and in the surface layers of the parent material. The plant residues are transformed by soil organisms into humus and other new organic substances. Earthworms , ants, termites, and other smaller animals come live in the soil and accelerate the organic transformations as well as promote the translocation of plant residues. Where rainfall is great enough to cause significant drainage to the groundwater, some of the dissolved materials may be completely removed from the developing soil profile (losses).
strong gleying (mottles caused by iron)
illuvial accumulation of OM (caused by rain water flowing from one layer to another)
accumulation of Fe and Al oxides
illuvial (caused by rain water flowing from one layer to another) accumulation of sesquioxides (free iron oxides)
silicate clay accumulation
distinctive color without clay
What defines a mollic epipedon?
A surface horizon, dark, thick (725 cm), high OM, > or = 50% base saturation
What defines an umbric epipedon?
A surface horizon, acidic Mollic, base saturation = 50%,
What defines an ochric epipedon?
A surface horizon, light colored, low OM, too thin for plants
What defines a histic epipedon?
O surface horizon, surface organic horizon, saturated as some time in year, 12-18% organic C
What defines a melanic epipedon?
A surface horizon, surface mineral horizon, black from high OM, high in allophane, developed from volcanic ash, >6% organic C, < 30 cm, thick and fluffy
What defines a cambic horizon?
weakly developed B horizon, evidence of color and/or struction development w/o clay accumulation (Bw)
What defines and Argillic horizon?
illuvial accumulation of silicate clays, clay films on peds, in pores, called clay skins or cutan (Bt)
What defines a spodic horizon?
illuvial accumulation, h-humus, s-sesquioxides, in coarse textured soils and cool climates (Bh, Bs, Bhs)
What defines a fragipan?
weakly cemented, dense horizon, > 50% of upland soils in the loess region, usually loamy textured (Bx, Cx)
What defines an oxic horizon?
highly weathered, accumulation of low activity clays, Fe & Al oxides, very low % BS (Bo)
moisture regime - saturated w/ water for sufficient periods of the year
moisture regime - humid climate, no water constraints
moisture regime - part of the growing season may be dry, plants might have problems finding water
moisture regime - dry, desert, very limited growing season
moisture regime - Mediterranean style, cool wet winter and dry hot summers
temperature regime - < 8 degrees C, cool summer
temperature regime - > 8 degrees C, warmer in summer
temperature regime - 10-15 degrees C
temperature regime - 15-22 degrees C
List, from order to series, the classification categories of soil taxonomy
only A horizon over C, found on or within parent materials, poor climatic conditions, considered other soils
immature, ochric, no Bt, resistant parent material
young, high porosity, formed from volcanic ash, highly productive soils, wind and erosion problems, Melanic, low bulk density
short wet periods, little leaching of cations, low OM, salt accumulations
frozen, permafrost, little development
must have >30% expanding clays, high expansion and contraction, self mising, big cracks, deep A, poor horizonation
Mollic epipedon, >50% base saturation, very fertile and productive
ochric or umbric (acidic mollic), well developed A, (E) B, C, Bt, >35% base saturation, generally forested soils
ochric or umbric, Bt, well developed horizon hoizons, acidic,
high sand content, ochric, usually have E, Bhs or Bs, highly leaches, very acidic, low base saturation, very infertile, forested areas (sand +pine) = ?
very highly weathered, tropicl, ochric or umbric, oxic subsurface horizons, low activity 1:1 clays, Fe and Al oxides, Bo, very low % base saturation
organic soil, histic, 12-18% organic matterial, saturated part of year, high water and nutrient holding capacity, low bulk density
Select items likely to be found in the standard format of a soil description
horizon designation, diagnostic horizon, horizon boundaries, description of horizon in typical pedon
Explain what content a county soil survey includes
a. general soil map – two parts, color map at approximate scale that shows the soil associations grouped into the main physiographic regions and an index map for the detailed map sheets
b. detailed map sheets – detailed soil map consisting of many individual map sheets
c. interpretive information – descriptive information from the over laying of the geographic information on the map so it can be used for land use of site planning. Usually soil profile descriptions and soil characterization date
What does sand influence soil properties?
high drainage rate, good aeration, rapid decomposition of organic matter, low susceptibility to water erosion, high pollutant leaching potential and low resistance to pH change and poor ability to store plant nutrients.
How does silt influence soil properties?
high water holding capacity, medium of most things, high susceptibility to wind and water erosion
How does clay influence soil properties?
high water holding capactity, poor aeration, very slow draingage, high soil organic matter level, high compactibility, low suceptability to erosion, shrink-swell, good sealing, low leaching potential, high ability to store plant nutrients and resit pH change
What can soil color determine?
drainage, weathering, OM, and soluble constituents
What darkens soils?
soil organic matter
What provides brown, red yellow, and orange colors?
What color does carbonates produce?
What color do reduced Fe oxides give soils?
gray and green colors
The more weathered a soil the more likely its color will be___ under oxidizing conditions
What does a dominant grey color mean?
What does gleying indicate?
highly reduced and poorly drained soils.
What are the four types of soil structures?
granular, platy, blocky, and prism
What soil structure is most prevalent in a B horizon?
What soil structure is most prevalent in an E horizon?
Where is granular soil structure most prevalent?
What is a granular structure?
circleish aggregates that are separated from each other in a loosely packed arrangement. Usually from less than 1 to as large as 10mm in d.
What is a platy structure?
relatively think horizontal peds or plates. can be inherited from PM
What is a blocky structure?
peds that are irregular, roughly cubelike, and range from 5 to 50 mm across. molded by the shape of the surrounding blocks
What is a prism like structure?
They are vertically oriented prism or pillar like peds that vary in height.
Describe the role of adsorbed cations have in flocculation of clays
The positively charged cations attract the negative charge of the clay platelets and forms a bridge between them holding the platelets together.
. Explain two physical-chemical and two biological processes influencing aggregate formation in soils
1. Mutual attraction of clay particles (flocculation)
2. shrink-swell of clay particles (vertisols)
1. Activities of soil organisms, assist in the formation of macroaggregates via bacterial polysaccharides & glomalin
2. influence of soil organic matter, major agent in temperate soils, provides substrate for microbial activities
Characterize a good seedbed
a. soil loose enough to allow easy root elongation and seedling emergence
b. firm enough to ensure the seed can easily imbibe water to begin germination
c. relatively free of large clods
Describe how soil crusting occurs, how it influences seedling emergence, and how conservation tillage could be helpful
The surface soil aggregates are overworked and under protected. When it rains the water splashes off and disperses fine clay particles that clog pores and seal the surface of the soil. This keeps the water out and it makes the seedlings have a hard time busting through. By leaving the materials on there, there is something to absorb the water and the soil is held in tact by the plant materials.
List five of the seven general guidelines for managing soil tilth
1. minimize tillage
2. timing traffic
3. mulching surface
4. add crop residues and animal manures
5. include sod crops
6. use cover crops and green manure crops
7. add soil conditioners (gypsum, organic polymers)
the hydrogen don't attach to the water evenly, they make a v-shape instead and this causes the positive charges to cling towards the side weighed down with the two hydrogens therefore causing this property of water
one of the hydrogens makes a low-energy bond to an oxygen particle from another molecule of water. this causes water to have a higher boiling point, specific heat, and viscosity
the attraction of water molecules for each other
the attraction of water molecules for solid surfaces, causes some water molecules to be held rigidly at the surface of soil solids
results from the greater attraction of water molecules for each other than for the air above, causes an inward force at the surface
h = .15cm2
In what type of soil does capillarity work?
All moist soils
What is the prime condition for capillarity?
medium to large sized capillary pores
How does capillarity work in sandy soils?
it permits rapi initial rise but limits ultimate height
How does capillarity work in clayey soils?
friction slows down the rate at which the water moves through the pores because they're really fine. Slow linitally but in time exceeds that of sand
How does capillarity work in loamy soils?
they are in the middle of clay and sand
force caused by adhesion, reduced the energy state of water near particle surfaces
force caused by cohesion, reduces energy state of water in the soil solution
force pulling the water downward
The absence of sharp breaks in the curves indicates a continuous range of pore sizes and therefore a gradual change in the water potential with increased soil water content.
Differentiate between gravimetric and volumetric water contents
Volumetric Water Content – volume of water associated with a give volume of dry soil
Gravimetric – direct measurement of soil water content: weigh it, heat it to get rid of all the water, weigh it again loss=water weight
Θv = Db x θm
volumetric water content, gravimetric determination of soil water content
gravimetric water content
mass of water / mass of soil
Define saturated hydraulic conductivity
Saturated hydraulic conductivity – the water hose for the flowing water, the thing through which the water can flow that controls the amount
describe how Ksat is related to soil uses
a. Beach sand – extremely high
b. Very sandy soil - too rapidly to filter pollutants in wastewater in a
c. Moderately permeable soil - it is suitable for most agricultural, recreational, and urban uses that require good drainage
d. Fine-textured, compacted or poorly structured soil - it is too slow for proper operation of septic tank drain fields, most types of irrigation and lost of recreational uses such as playgrounds
e. Compacted clay – extremely slow, good for wastewater lagoon lining or landfill cover material
Compare and contrast the concepts of infiltration and percolation
a. Infiltration – process by which water enters the soil pore spaces and becomes soil water, takes place at the soil surface
b. Percolation – process by which water moves downward into the profile, rate is related to the soil’s hydraulic conductivity
Explain how diverse surface soil textures influence infiltration rates over time
Water enters a dry soil rapidly at first but slows as the soil becomes saturated.
Sandy soils have the least decline.
Soils with high amounts of expansive clays have a high initial infiltration rate when cracks are open but very low when the clay swells with water and closes the cracks.
explain how soil stratification affects water movement
The water is attracted to the fine-textured soil only when the water content is raised a bunch will the water begin to move to the sand.
What is maximum retentive capacity?
– all soil pores are filled with water, matric potential is close to zero, the soil will remain here only so long as water continues to infiltrate
What is field capacity?
when water addition stops the largest pores will drain downward rapidly, when this flow becomes negligible it is at field capacity. Soil is holding the maximal amount of water useful to plants, it is near its lower plastic limit, and sufficient pore space is filled with air to allow optimal aeration for most aerobic microbial activity and the growth of most plants
What is the wilting coefficient?
the rate of plant water removal fails to keep up with the plant needs so the plant wilts. At first they can keep up by absorbing a lot at night when water isn’t being lost through leaves but eventually they loose so much they can’t catch up and are wilted night and day
What is the hygroscopic coefficient?
soil moisture is lowered below the wilting point, the water molecules that remain are very tightly held, most are absorbed by colloidal soil surfaces the water is held so rigidly that most of it can only move in the vapor phase
Describe how soil texture and organic matter content influence available water holding capacity
As fineness of texture increases there is an increase in available moisture storage. Sand to loam to silt loam. But clay soils have a higher wilting coefficient so they tend to provide less water. OM has a very high water-holding capacity. It also affects it indirectly because of its influence on soil structure and total pore space.
Describe how vegetation type influences the fate of precipitation and irrigation
grasslands and forests protect the soil from the raindrops and enourage water infiltration and decrease likelihood of runoff
Describe how stem flow influences the fate of precipitation and irrigation
water is directed down the plant to the stem and flows downward in this way, increases the opportunity for saturated flow to occur
Describe how soil management influences the fate of precipitation and irrigation
– Enhance soil surface storage to allow more time for infiltration. Maintain dense vegetation during period of high rainfall (cover crops). Maintain soil structure by minimizing compaction.
Describe how urban watersheds influence the fate of precipitation and irrigation
curtailed infiltrating capacity and saturate hydraulic conductivity because of heavy equipment use in preparing land increases surface runoff. Leads to erosion and severe environmental problems
Identify the two major points of resistance to water movement in the soil-plant-atmosphere continuum
1. the rate at which water is supplied by the soil to the absorbing roots
2. the rate at which water is transpire from the plant leaves
Explain how vegetative, paper and plastic mulches, along with crop residues and conservation tillage not only reduce surface evaporation but also provide other benefits
Vegetative mulches – most practical for small areas, provides clean path for foot traffic, reduces weed growth, moderate soil temperatures prevent overheating, increase in water infiltration, provides organic matter and plant nutrients, encourages earthworm populations, reduces soil erosion
Paper and Plastic Mulches – widely used for vegetable and small fruit crops, increases in plant growth,
Crop Residue and Conservation Till – increase infiltration,
explain why a deep well would be more likely to provide high quality drinking water than a shallow well
It would not come into contact with the pollution plume because the water wouldn’t be moving very much or coming into contact with extraneous things
Identify three principal factors which regulate soil aeration
soil macroporosity, soil water content, and O2 consumption by respiring organisms
Contrast the composition of soil air with that of the air above the soil
soil air has lower amounts of O2, higher CO2, is much higher in water vapor, and under waterlogged contions the concentrations of gases such as methane and hydrogen sulfide are much higher
Describe how (and why!) the forms of Fe and N are influenced by poor soil aeration
If there’s not enough O2 anaerobic microorganisms are there and they have to use other substances and iron is commonly used. Their use of Fe reduces its presence in the soil. They could possibly use N too. It’s an oxidation-reduction reaction. Nitrogen is the next most easily reduced substance next to water.
What are the factors involved in the process of wetland delineation?
how water flows in and out of a wetland. In through runoff, groundwater seepage and precipitation. Out by surface and subsurface flows, evaporation and transpiration. Hydroperiod is the pattern that things change, ex. Seasonal, daily, etc. The slower the water moves through the better cause more reactions have time to take place.
What are the factors involved in the process of hydric soils?
Hydric soils are mostly histosols, in the aquic suborder. Generally have an aquic or peraquic moisture regime. They are subject to periods of saturation that inhibit the diffusion of O2 into the soil, they undergo reduced conditions for substantial periods of time (this means electron acceptors other than O2 are reduced, they also exhibit certain features termed hydric soil indicators.
What are the factors involved in the process of hydrophytic vegetation?
– plants that have evolved special mechanisms to adapt to life in saturated, anaerobic soils.
. Explain how progressively warmer soil temperatures influenced microbial respiration
It increased it, the rates more than double for every 10o C rise.
). Address items which relate soil temperature to soil depth and month of the year.
Temperature is less variable at greater depths, surface soil temp changes with the air temp.
Relate intensity of tillage to soil temperature
The more intense the tilling the higher the soil temp.
What is a defining characteristic of crystallin silicate clays?
They are predominately negatively charged
What are some defining characteristics of noncrystalline silicate clays?
high amounts of both positive and negative charge and high water-holding capacities, extremely high capacities to strongly absorb phosphate and other anions
What are some defining characteristics of iron and aluminum oxides?
net charge ranges from slightly negative to moderately positive, low in plasticity and stickiness
What are some defining characteristics of humus?
very high capacities to absorb water, almost no plasticity or stickiness, high amounts of both negative and positive charge but net charge is always negative
What is a tetrahedral sheet?
an interlocking array of tetrahedra composed of Si surrounded by 5 O each sharing its basal oxygens with its neighbor
What is an octahedral sheet?
Six oxygen surrounding an aluminum or magnesium atom that form an eight sided geometric solid
What is isomorphic substitution?
the process by which one element fills a position usually filled by another of simlar size.
What is kaolinite?
1:1 clay, layers stack vertically, low surface area, low water holding capacity, low negative charge, mostly pH dependent, very little isomorphic substitution, little shrink swell
What is smectite/vermiculite?
2:1 expanding clay, when wet it expands, high surface area, Mg subs for Al, high water holding and swelling, high surface charge
What is fine-grained mica/chlorite?
2:1 non-expanding clay, substitution in the tetrahedral sheets, net negative charge, potassium keeps the layers collapsed, moderate surface area, water holding capacity and surface charge, pretty easy to manage
What is the history of Kaolinite?
Kaolinite has been used for thousands of years to make pottery, roofing tiles, and bricks
Contrast non-silicate colloids with silicate clays
they rarely have isomophrous substitution, do not ahve a large negative charge, the surfaces of these clays can strongly absorb anions, they are not expansive, quite stable for construction pruposes, and generally exhibit realtively little stickiness, plasticity, and cation adsorption
What is the source of a constant negative charge on a silicate clay?
isomorphouse substitution of a lower-charged ion for a higher charged ion.
What is the source for a constant positive charge on a silicate clay?
isomorphouse substitution is lso a source of positive charge if the substituting cation has a higher charge than the ion for which it substitutes
What is the source for a pH-dependent negative charge?
broken edges of mineral colloids, hydroxyl (OH) groups on the surfaces of inorganic and organic colloids
What is the source for pH-dependent positive charges?
under moderate to extreme acid soil conditions, some silicate clays and Fe, Al oxides may develop positive charges by protonation
What is protonation?
the attatchment of H+ ions to the surface of OH groups
What is reversibility
exchange reactions are rapid and reversible
What is charge equivallence?
Exchange takes place on a charge for charge basis, you have to keep the same amount of charge
What is ratio law?
At equilibrium, ratio of similar cations on exchange sites will be the same as that in the solution
What are anion affects on mass action?
anions are always present, the type of anion will influence the direction and equilibrium of the reaction. If the anion causes precipitation, volatilization, or strong association then the reaction goes right
What is mass action?
an exchange reaction will be more likel to proceed to the right of the released ion is prevented from reacting in the reverse direction
What is cation exchange capacity (CEC)?
the sum total of exchangeable cations that a soil can absorb
How do you estimate clay mineralogy from information found on CEC?
If you know a soils pH, clay content, and organic matter levels you can estimate clay mineralogy
What clays mostly compose Aridisols and what are there CEC's?
Smectice and Fin-grained mica, middle range, low range
What clays mostly compose vertisols and what is their CEC?
Smectice, middle CEC
What clays mostly compose mollisols and what is their CEC?
What clays mostly compose Alfisols and what is their CEC?
everything except Fe, AL oxides. low to upper middle range CEC
What clays mostly compose Spodosols and what are their CEC?
Fe, Al oxides and Kaolinite, very low CEC
What clays mostly compose Ultisols and what are their CEC?
Fe, Al oxides and Kaolinite, very low
What clays mostly compose Oxisols and what are their CEC?
Fe, Al oxides and Kaolinite, very low CEC
How does pH affect CEC?
As pH rises there is more pH dependent charge
What is the equation for pH?
pH = -log [H+] ex. if [H+] = 10^-5 M log 10^-5 = -5 pH = 5
Identify the sources of added hydrogen ions
carbonic acid, accumulation of organic matter, oxidation of nitrogen and sulfer, acids in precipitation, and plant uptake of cations
Explain how leaching loss of cations can acidify soils over time
the H+ ions exchange with the nonacid ions and then they are free to be leached away along with accompanying anions and then the soil become dominated by acid cations such as H+ and Al3+
Explain how aluminum is involved in soil acidity
When H+ ions are absorbed they attack the structure of the minerals and release Al3+ ions which become adsorbed on the colloid's cation-exchange sites. The Aluminum is highly toxic to most organisms and it lowers soil pH because it splits water molicules and combines with OH and leaves H in the soil
Define active acidity
the H+ ion activity in the soil solution
Define exchangeable acidity
the pool of acidipty that is salt replaceable.
Define residual acidity
hydrogen and aluminum ions that are bound in nonexchangeable forms by organic matter and clays
Why is PhKCL different from Phwater?
KCL depends on the ion exchange capacity and type of colloids
Describe how humans have influenced soil acidity through nitrogen fertilization and acid rain
Excess N fertilization leads to nitrification which acidifies soil. Fossil fuel combustion and burning things leads to acid rain which acidifies soil.
Describe toxic effects of Al, Mn, H, and Fe on plants in low pH soils.
Aluminum toxicity affects plants by inhibiting root growth and bacteria. Symptoms are stunted root systems and leaves with chlorotic (yellowish) spots. Manganese toxicity affects plants when too much is taken up, symptoms vary but include crinlking or cuppin of leaves and intereinal patches of chlorotic tissue. Hydrogen Toxicity can damage the root membranes and kill beneficial soil bacteria. Iron toxicity is common in acidic rice paddies.
What is the optimum range for soil pH for plant growth?
Describe how liming materials do their job
they react with carbon dioxide and water to yield bicarbonate when applied to an acid soil
Identify the four key factors influencing the amount of liming material needed to correct acid soil conditions
1. the change required in the pH or exchangeable Al saturation
2. the buffer capacity of the soil
3. the amount or depth of soil to ameliorate
4. the chemical composition of the liming materials to be used
5. the fineness of the liming material
Blueberries, rhododendrons, and azaleas enjoy pH values of 5.0 and below. Describe how to reduce soil pH to accommodate these unusual plants
add acid-forming organic and inorganic materials
ogranic-pine needles, sawdust, acid peat moss
inorganic-aluminum sulfate or ferrous sulfate
Relate the benefits and downsides of earthworms on soil properties
- burrows allow roots to penetrate
- enhances aggregate stability of the soil
- enhance soil fertility and productivity by altering chemical conditions in the soil
- increase aeration and drainage
- relieve compaction
- leaves soil surface bare of residues
- rapidly percolating water can lead to extensive chemical leaching
How do earthworms affect nitrogen?
They make it available for biological processes
explain how earthworms can be a very unwelcome addition to forest ecosystems in northern Minnesota
The soil there developed without earthworms and therefore the species need a thick forest floor and when the earthworms mix it up the stuff that lives there no longer can
Explain how mycorrhizal fungi help higher plants
they improve P availabilty and water uptake
Describe the prevalence and activities of soil algae, fungi, bacteria, and actinomycetes
Soil Algae- produce organic atter and have favorable effects on soil aggregation
Fungi - there are tons, humus formation and aggregate stabilization and decomposition
Bacteria - participate in virtually all of the ogranic transactions that characterize a healthy soil
actinomycetes - the most abundant prokaryote, decompose stuff
List six major beneficial effects of soil organisms
Organic Material Decomposition, Breakdown of Toxic Compounds, Inorganic Transfomations, Nitrogen Fixation, Rhizobacteria, and Plant Protection
Explain what is known about how Pseudomonas bacteria inhibit the take-all fungus of wheat.
the buildup of the pathogen over the first few years is eventually overshadowed by a subsequent buildup of specific organisms antagonistic to the pathogn
Describe how the various classes of microbes “get along” with each other
- microbiotic crusts of arid rangelands are intricate living systems that greatly benefit the associated natural vegation communities and consis of mutualistic associations with algea, fungi, mosses, bacteria, and liverworts
- changes in environment affect both the number and kinds of soil organisms
- the communities of plants and animals aboveground is greatly influence by the belowground communities
Evaluate the influence of no-till compared to plowed conditions in Georgia
fungi are higher in no-till but bacteria and protozoa are higher in plowed
Categorize organic compounds in the soil as to their rate of decomposition
- Sugars, starches, and simple proteins
- crude proteins
- fats and waxes
- lignins and phenolic compounds
Compare and contrast degradation of organic matter under aerobic and anaerobic conditions
Aerobic- decomposition, breakdown of cellulose and starch, breakdown of proteins, breakdown of lignin, organic decay
Anaerobic- bacteria and archaea in wet soils, it releases relatively little energy for the organisms involved
Compare the C/N ratio of various organic materials
high- sawdust, newspaper, spodosol O horizon
low - hairy vetch, broccoli residue
If the C/N ratio of an organic material exceeds 25:1, two negative consequences result. List those two consequences, and describe why they occur
it will deplete the soil's supply of soluble nitrogen and cause plants to suffer from nitrogen deficiency. Secondly, the decay of organic materials can be delayed. the plants have to take N from other places because it's not readily available
Categorize the types of soil organic matter and the transformations among them
Detritus:identifiable dead tissue
Humus: (Humic and Nonhumic) nonliving nontissue
List 5 positives for the environment which can result from increasing soil organic matter
less flooding, less pesticides are needed, greater groundwater recharge, less water polution, less land degradation
List and defend five general guidelines for managing soil organic carbon
A continuous suply of plant residues must be addd to the soil to maintain an appropriate level of soil organic matter
There is no ideal amount of soil organic matter. Do not try to maintain a higher SOM level than needed
Adequate nitrogen is requisite for adequate OM because of the relationship between nitrogen and carbon in humus and because of the positive effect of nitrogen on plant productivity
Tillage should be elimnated or limited.
Perennial vegetation should be encouraged to leave land relatively undisturbed
gravimetric water content (Mass water content)
mass of water / mass of soil
For the macronutrient nitrogen, describe its role in the plant, plant deficiency symptoms, response to oversupply, and forms taken up by plants
A major part of amino acids, nucleic acids, and is essential for carbohydrate use within plants. if deficient plants tend to exhivit chlorosis (yellowish or pale green leaf colors). If too much is applied excessive vegetative growth occurs, the cells of the plant stems become enlarged but relatively weak and plants become top heavy and fall over. It is taken up by plants as dissolved nitrate (NO3-) and ammonium (NH4+)
What are the five possible fates of ammonium and four possible fates of nitrate.
- plant uptake
- adsorption or fixation
- Leaching loss
- plant uptake
What is volatilization?
it's when NH4 turns into NH3 (therefore solid turning into a gas)
What is dentrification?
an anaerobic process by which heterotrophic bacteria reduce nitrate to such gases as NO, N2O and N2
Explain how mineralization and immobilization counteract each other
they are the same equation going in opposite directions
Give the reason why ammonium fixation, on a percentage basis, is higher in subsoil than in topsoil
due to the higher clay content of subsoils
Describe the mechanisms of ammonia volatilization
NH4 dissolves with OH to form water and NH3 (gas)
Reproduce the equations for the two steps of nitrification, including the energy production, and discuss the soil conditions influencing this important process
NH4+ + 1.5 O2 --> NO2 + 2H + H20 + 275 kJ energy
NO2 + 0.5O2 --> NO3 + 76 kJ energy
needs to be an abundance of exchangeable Ca and Mg, high smectite or allophane clays are bad. need well-drained soils
Leaching of nitrates costs crop productivity and adversely impacts the environment. Explain why this is so
negatively charged nitrate ions are not adsorbed by the negatively charged colloids that dominate most soils and therefore the nitrate ions move downward freely with drainage water and are readily leached from the soil
Why is soil nitrate lower when plants are grown?
because much of the nitrate formed is removed by plant uptake
Identify the causes of hypoxia in the Gulf of Mexico
the nitrogen stimulates more growth of algea which sinks to the bottom when it dies and the microorganisms deplete the oxygen in the water when they decompose this tissue. This leads to hypoxia which is a state of low oxygen in water.
Describe the conditions under which denitrification can cause gaseous losses of soil nitrate
lack of free O2
available organic C
warm soils best
saturation for only a few hours
Write out the general reaction for biological nitrogen fixation
NH3 + organic acids amino acids Proteins (plant or bacterial)
Describe the symbiotic relationship between leguminous plants and either Rhizobium or Bradyrhizobium bacteria
Rhizobium forms nodules on the roots
For the macronutrient phosphorus, describe its role in plants, along with its plant deficiency symptoms
a limiting nutrient, P deficient symptoms include stunting and purpling, enhances photosynthesis, important for structural tissues, root growth, seed production, and flowering
Three aspects of the phosphorous problem
total P is generally low, mostly unavailable, added H2PO4 is fixed
Describe how (and why!) applications of P fertility in the US, developed, and developing regions have changed over the past decades.
it has remained pretty steady in the US, is leveling off in developed countries, and is continuing to increase in developing countries
Sequentially describe the process of P-induced eutrophication
algae and plants cover the surface of the water
they die and sink to the bottom
microogranisms use up the oxygen dissolve in the water to decompose them
the decrease in oxygen severely limits the growth of many aquatic organisms
Why do P pools differ so much between forest and agricultural watersheds
because the addition of fertilizer results in inorganic P accumulating in the soil
List five of the seven approaches for practical management of soil P
- adjust application to soil status
- localized placement
- combine ammonium with posphorus
- cycling of OM
- control of soil pH
- enhance mycorrhizal symbiosis
- choose P-efficient plants
Describe 4 steps to keep P from getting into water.
- avoid excess accumulation
- minimize loss in funof and sediment
- capture P from runoff
- tie up P with inorganic amendments
For the macronutrient potassium, describe its role in plants and its plant deficiency symptoms
third most limiting nutrient in crops, important for osmotic regulation, photosynthesis, starch formation and sugar translocation, helps adapt to environmental stress, deficiency symptom - necrotic leaf edges
Compare K with N and P for its environmental impacts.
it doesn't really have any
Describe why liming acid soils can reduce leaching losses of K
the complementary ion effect, the K easily replaces Ca
Explain the potassium-related concept of luxury consumption
plants can take up far more than they need
Compare the plant availabilities of soil K sources
K in primary mineral structure- unavailable
non exchangeable K in secondary mineral - slowly available
exchangeable K on soil colloids and K soluble in water - readily available
sort out four practical recommendations for effective
- apply less K at a time but more often
- apply lime to acid soils
- capitalize on k supplying power of soils
- whole plant removal depletes K more rapidly thus return of plant residues is very important
List and describe each of the four goals of nutrient management
- cost effective plant production
- efficient use/conservation of nutrients
- enhance soil quality
- protect the environment
Explain how nutrient management plans work
they attempt to balance the inputs of N and P with their desirable outputs to prevent undesirable outputs. it specifies practices for how nutrients will be used in plant production
Of the many available best management practices, our text discusses four: buffer strips, cover crops, conservation tillage, and forest stand management. Prepare a schematic diagram of a “multi-species riparian buffer strip”
Explain why Figure 16.8 shows rye is a better cover crop than vetch.
rye adsorbs more left over stuff
Identify the amount of the soil surface which must be covered with plant residue under conservation tillage.
at least 30%
Sort through pages 688-691 to find ways in which clear-cutting affects nutrient losses from forested lands
leaching and runoff, erosion of litter, and volatilization in fire
Most forests are not fertilized. Describe how these ecosystems conserve nutrients
recycling stuff ( OM mineralization) and surface soil enrichment (by acting as nutrient pumps or fixing nitrogen)
Describe the best ways to make use of animal manures for crop production
liquid vs. dry storage
Identify limitations in using sewage sludge as a nutrient resource
Convert %P2O5 to %P
Multiply by .44
Conver %K2O to %K
Multiply by .83
A soil fertility “diagnostician” must be a bit like a detective to be effective. List the text’s five guidelines for success
- organize a record of your observations
- interview landowner or manager
- look for spatial patterns
- examine plants, especially leaves, for nutrient dificiency symptoms
- measure shoot and root growth, check for symbiotic associations
Soil analysis requires three successive steps; list each one
- Sampling the soil
- chemical analysis of the sample
- interpretation of the results
Advise a rookie on how to take representative soil samples from his field
take samples from obviously different areas, take 12-15 samples per area, sample at the same time of the year
Describe how the site-index approach to phosphorus management works
researchers have integrated phosphorous source, transport, and management charateristics of a site into an index of phosphorus polution risk.
Contrast geological and accelerated soil erosion
geological is always occuring w/o the influence of humans, human disturbance accelerates soil erosion
Identify the three main types of water erosion
Sheet erosion, rill erosion, gully erosion
Differentiate among the five conservation tillage systems
no till- soil undisturbed prior to planting in a narrow seedbed
ridge till- soil undisturbed prior to planting which is done on ridges higher than row middles. residues are moved aside of incorporated on about 1/2 of soil surface
strip till- soil undisturbed prior to planting, narrow and shallow tillage in row using rotary tiller, in row chisel, etc.
mulch till - surface disturbed by tillage prior to planting but at least 30% of resue left on or near surface tools such as chisels, field cultivators, disks, ect are used
reduced till - any other tillage and planting system that keeps at least 30% of residues on surface
Identify the factors that are involved in the RUSLE and describe how they influence soil loss
R-Rainfall factor - driving force for sheet and rill erosion
K-soils susceptibility for erosion - amount of soil lost per unit of erosive energy
LS- topographic factor - as slope length increases and steepness increases erosion increases
C- cover or management - depends on the amount of tillage and the amount of surface residue left
P- support practices aimed at guiding and slowing runoff
Describe how conservation tillage affects soil physical, chemical, and biological properties
OM levels increase
Earthworms numbers are elevated
Aggregation goes up
Infiltration and percolation both improve
Soil water holding capacity is enhanced
Soils cooler, wetter (can be negative in spring)
May have more immobilization and denitrification
Surface pH may drop