Soil exam #2

al1/22/24

• Soil connects all spheres of earth's functions

Hydroponics system for a plant 

• Water intake/ transpiration to survive as well 

• Nutrients - macro and micro 

• Temp / air support and oxygen and CO2

• Sun

• Physical support - an anchor for root systems 

• Protections from toxins 

CHONSP

Carbon, hydrogen, oxygen,  nitrogen, sulfur, phosphorus 

• Make up >95% of all living tissues 

• CHO are gotten from air and water

• NSP are derived from soil 

Integrating components of soil

• Sand, clay 

• Composition of an ideal soil by volume 

Sand, silt and clay 

• All behave differently in soil because of their surface area to mass ratio 

• Smaller particle size gives rise to greater surface area per unit mass in turn increasing particle’s interaction with each other, water and nutrients.

Detritus, roots, microbes - organic part of soil

• Organic part of soil

• Wouldn't pass a 2mm sieve 

Soil Organic Matter (SOM)

• Foot source for most soil microorganisms

• Source of soil fertility 

• Profound effects on soil structure and water storage 

• We can see particle size distribution based on organic matter concentration 

Eolian, Pedon

• Larger product of soil formation/classification

• Solid formed on parent material transported by wind (eolian) 

• Soil ped - layers of soil 

Integrating components of soil 

• Water 

  • Soil water 

  • Soil stores precipitation and irrigation, making water available to plants between rainfall or irrigation events

  • Retains water between precipitation events

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The rock cycle 

• Areas can have different rocks due to different types of additions to the soil and actions 

• Metamorphic rock can be caused by tectonic activity and heat 

Weathering proceeds continually at the surface of the earth changing rocks and minerals into 

1. Smaller versions of themselves (Via Physical disintegration)

   1. Temperature - variable expansion and contractions of different minerals which can be accelerated by ice 

   2. Abrasion  - rock particles collide with each other due to the action of water, ice and wind 

2. Chemically altered versions (via chemical decomposition)

   1. Six main processes of chemical decompositions

   2. Hydration, hydrolysis, dissolution, acid reactions, oxidation reduction, and complexation

      1. They occur in presence of water and water is often a reactant 

      2. Some of them occur due to the presence of acids produced by roots, microbes, or air pollution (organic or inorganic)

      3. Their products can be new minerals, or can be solutions

      4. Rate of chemical decomposition increases with surface temperature and area 

3. What area would you see more weathering? Rainforest or Desert?

Weathering: Breakdown of rocks into smaller pieces or transformation into chemically altered versions of themselves 

Erosion:  Transport of rocks, sediments, and soils from one location to another

Hans Jenny’s 5 soil forming factors (CLORPT)

1.  S = f’(cl’,o’r’p’t’)

2. Parent material (p’) / r / regolith 

   1. Alluvial - transported by streams or rivers 

      1. Stream water erodes and transports parent materials which are then deposited when water slows own

      2. Intermittent nature of flooding can lead to layering of parent material deposition

      3. Generally, alluvial soils have characteristics desirable for human settlement 

      4. Nile delta, willamette valley oregon 

   2. Lacustrine - deposited in lakes

      1. By the time sediment is carried to the middle of a lake, only smaller particles remain

      2. Therefore lacustrine deposits are devoid of coarse particles such as coarse sand or gravels

      3. They also are characterized by thin layers that reflect annual deposition of sediments 

      4. Slump / bedrock 

   3. Marine - deposited in oceans

      1. Marine deposits can be formed from eroded sediments

      2. They can also be formed from the accumulated bodies of marine algae (coccolithophores - armored ocean algae) which when uplifted can form limestone cliffs 

   4. Colluvial - transported by gravity 

      1. Are not set down and sorted, the different sizes are all intermixed 

   5. Eolian - transported by wind 

      1. Wind transported material can be any size (sand, silt, clay)

      2. Eolian deposits can be in a homogenous unit or can exhibit some layering 

      3. Arid environments are most commonly associated with aeolian sand deposits, while glaciers are associated with more loessal (silt) deposits 

   6. Glacially-transported materials - till, moraine , outwash 

      1. Till = unsorted debris deposited directly by ice 

      2. Moraine = landform of debris left by glacier 

      3. Outwash = debris sorted by meltwater

      4. Glacial loess - parent material that is physically weathered by ice into silt, then transported by wind, laid down in homogenous deposit, no layering 

   7. There are both Erosional and depositional landforms - we focus on the depositional landforms transported soil parent materials. 

   8. Organic parent materials 

      1. Peat bog with materials that would break down instead take content of peat ~

3. CLIMATE 

   1. Wetter and wetter conditions create deeper soil profiles and greater excited of mineral weathering because 

      1. Biochemical reactions increase with temperature doubling with every 10 degrees C

      2. Water is a key ingredient for chemical weathering 

   2. To fully promote soil development water must not nly  … participate in weathering reactions but also percolate through profile to translocate soluble weathering products

   3. At given site with 600 mm of rain effective rainfall (the water weathering the profile ) could vary depending on 

      1. the seasonal distribution of rainfall 

      2. Topography of an area 

      3. Temperature and evaporation  

      4. Soil permeability

   4. Which of the following scenarios would you expect to have greater effective distribution 

Soils contain organic matter which contains carbon, plants get most carbon from soil —- FALSE

4. Organisms 

   1. Plants add organic matter to soil (while living and when they die)

   2. Different climates exercise an influence on soil formation

      1. Directly through their influence on water availability for weathering 

      2. and indirectly - through modifying plant productivity and therefore, quality of organic matter that plants can return to soi

   3. Eastern hemlock vs sugar maple 

      1. Sugar maple has calcium content of 5x vs hemlock has 1x because they transfer their calcium to roots vs leaving in leaves 

      2. Subsoil fine root abundance << subsoil fine root abundance bigger in sugar maple soil 

      3. Sugar maple mines subsoil for Ca =, transporting it to leaves, whos leaf fall then helps to create organic - matter rich topsoil which then retains Ca (relative to hemlock)

   4. Bioturbation - disturbance of sediments by living organisms 

   5. Krotovinas - an animal burrow that has been filled with organic material or mineral from another soil horizon 

   6. Darker areas in Bk horizon are crotovinas which are animal burrows filled with natural soil

5. Relief or topography 

   1. A catena is a sequence of soils down a slope with solid identified in 5 consistent positions

      1. Summit - top of hill 

         1. Residual parent material

      2. Shoulder - slope

         1. Redidual/colluvial 

      3. Backslop - steepest 

         1. Colluvial

      4. Footslope- towards bottom 

         1. Colluvial

      5. Toeslope 

         1. Alluvial 

   2. Aspect 

      1. Northern hemisphere slope facing south, exposed more to sunlight and will have less organic matter and will be less weathered compared to north facing

6. Time 

   1. Processes that happen over time

   2. Four soil forming processes happening in time

      1. Additions 

         1. Organic matter from plants (carbon is coming from atmosphere)

         2. Wind blown dust

         3. Salts dissolved in groundwater, that rise to surface with evaporation

      2. Losses 

         1. Leaching of dissolved materials to ground water 

         2. Erosion of surface materials

         3. Transform to gas (Volatilization, microbial respiration)

      3. Translocations 

         1. Movement of material vertically or laterally 

         2. Dispersed fine clays dissolved salts dissolved organic matter

         3. Usually due to water, which could be downward (Gravity) or upwards (capillary action rise)

      4. Transformations 

         1. Chemical or physical transformations of soil constituents, to synthesis of new compounds

         2.  Often, new silicate clays or hydrous oxides of Fe and Al

         3. Also, decomposition of plant inputs into soil organic matter

The soil profile 

• A vertical section of soil showing the various horizons from the surface to the unaffected parent material 

• A horizon is “A layer, approximately parallel to  the surface of the soil that is distinguishable from adjacent layers by a distinctive set of properties produced by the soil process 

  • O horizon - organic material not mixed with minerals 

    • Oi - decomposed organic matter

    • Oe - moderately decomposed organic matter

    • Oa - highly decomposed organic matter

  • A horizon, highest density of root growth, leading to organic matter deposition from roots

  • E horizon - zone of eluviation, or leaching must be underlain by B horizon, but can be in place of an A horizon 

  • B horizon - a zone of illuviation - or accumulation due to the leaching from above horizons of: Fe and Al oxides, Ca carbonate and Ca sulfate

  • C horizon - less affected by soil forming processes + outside zone of major biological influence; may have accumulation of Ca, MG, carbonates, sulfates

  • R/ (Regolith) = unaltered parent material - likely rock 

• Why do E horizons occur in forest but not in grassland soils

  • Possible reasons: 

  • Greater rainfall in forests -> greater effective precipitation for leaching

  • More acidic leaf litter in forests (compared to more neutral pH roots of grasslands -> more organic acids in leaching processes

  • Organic inputs more stratified to O horizon (from leaf fall) rather than distributed throughout surface soil ( as in grasslands) → fewer high-activity surfaces in surface soil

• Time as a soil forming factor 

  • Warm humid climate residual parent igneous material 

  • Soils generally develop more prominent layers over time 

  • Warm, subhumid climate

  • Calcareous loess parent material

“Weathering age” is distinct from chronological age 

• Parent material could be exposed for a long time, but in some environments insufficient water for soil development vs

• Warm humid environments with abundant vegetation would accelerate soil weathering

Think of CL O R P T, rather than CL + O + R + P + T

Transition horizons and subdivisions within horizon 

• Transitional horizons that combine properties of two horizons, dominant listed first

• Subdivisions within horizons 

• Used to differentiate differences in structure or color within a master horizon.

Sub Horizons -  More specific designations of master horizons but their formation can be pronounced 

EX;

• b - buried horizon 

• Ap - ploughed horizon

• k - accumulation of carbonates

• kk- engulfment of carbonates 

• t - accumulation of silicate clays 

• w - Distinctive color or structure without clay  accumulation 

Soil Classification 1

• Humans like to organize things - taxonomic classes of plants/animals 

• World reference Base (WRB)

  • An international system for soil classification, supported by FAO, UNESCO and other orgs

• Soil Taxonomy 

  • Developed by USDA, most commonly used in U.S. because we have to be different…

• 6 Taxonomic levels in USDA soil

  • Criteria for classification encompass chemical, physical, and biological processes

    • Temperature and moisture status throughout year

    • Color, texture, structure of soil

    • Contents of organic matter, aFe, Al, SIlicate clays, salts, the pH

  • Precise soil classification using this taxonomy may be expensive or time consuming 

• Cation Exchange Capacity (CEC)

  • Fundamental soil property 

    • Plant nutrient availability and retention

  • Total quantity of negative surface charges

  • Sum of cations: base cations + acid Cations

    • (Ca+Mg+K+Na)+(H+Al)

• Base saturation

  • Percent of CEC occupied by base cations 

  • Base saturation (%)

    • =(Ca+Mg+K+Na)/CEC

  • Increases as pH increases

• Diagnostic horizons 

  • Horizons whose presence or absence indicates a soil’s location in the taxonomy 

  • Epipdeon 

    • Surface diagnostic horizon 

    • A,E, or sometimes upper part of B

  • Subsurface diagnostic horizon 

    • Usually B, sometimes E or C

  • Mollic  Epipedon 

    • From latin mollis, Meaning soft

    • >0.6% organic C

    • Generally >25cm thick

    • Softness even when dry

    • High base saturation (>50%)

    • Moist at least 3 months of the year 

    • Characteristic of grasslands

  • Umbric epipedon 

    • From latin Umbra, meaning shade 

    • Similar to the mollic epipedon EXCEPT

    • %base saturation is lower

    • Develops in higher rainfall areas and w parent materials low in Ca and Mg

  • Ochric epipedon

    • From greek ochros, pale

      • Too thin

      • Too light in color or

      • Too low in organic matter to be mollic or umbric 

    • Due to low organic matter content, may be hard and massive when dry

    • The “wimpy” a 

  • Histic epipedon 

    • Greek Histos tissue

    • A thick surface organic horizon that is 20-60 cm thick overlying mineral soil 

    • Formed in wet areas, it is a layer of peat or much with very dark color. 

• Diagnostic subsurface horizons 

• Important for illuvial material to have been transported 

and 

• Entisols 

  • Recent soils: mineral soils with little to no evidence of pedogenic horizons

  • No diagnostic horizon other than ochric epipedon

  • Found on landscapes where soil parent material is in no place long enough to pedogenetic processes to act

• Inceptisols 

  • More strongly developed soil profiles than those of entisols, but too weakly developed to meet criteria for any other soil horizon 

  • Ochric or umbric epipedon, cambic horizon

• Gelisols 

  • Greek gelic, very cold

  • Permafrost present within specified depth

  • Over permafrost, gaelic materials “mineral or organic soil materials that show evidence of cryoturbation (frost churning) or ice segregation

  • May have diagnostic horizons 

  • Cryoturbation

    • Mixing of materials form various horizons, down to bedrock, due to churning actions of repeated freeze/thaw

• Andisols

  • Jap. ando, black soil

  • Soil developing pon volcanic ejecta

  • Dominated by allophane and “al-humus” complexes 

  • Accumulation of organic matter complex with Al

  • May have diagnostic horizon and occur at any temp, or moisture, or elevation 

• Aridisols 

  • Latin aridus - dry 

  • Dry environment: no period of 90 consecutive days when moisture is contoniusly available for plant growth 

  • Ochric epipedon, sometimes argillic or natric horizon 

• Histosols 

  • Gk, histos , tissue 

  • Accumulation of organic material due to wetness (in absence of permafrost)

  • Organic material is more than half of top 80cm

  • Can occur in any climate but most prevalent in cold

  • Precursor to coal 

  • Usually bog like

• Vertisols 

  • L. Verto, turn 

  • Dark swelling and cracking clay (>30% clay)

  • Problematic for constriction of any sort

  • Challenging for agricultural use: “24 hour soils”

  • Shrink/swell can impede infiltration in wet vertisols

• Alfisols 

  • Occur in cool to hot humid areas, usually forested

  • Diagnostic sub horizons: Bt or Btn, >35% base saturation

  • Overlain by ochric or umbric epipedon 

  • trees

• Mollisols 

  • L, Mollis, soft,

  • Accumulation of organic matter form grassland root systems; rich in Ca

  • Have a mollic epipedon

  • May have argillic, natric, or cambic subsurface horizons, but NOT oxic or spodic horizons

  • Prairies with old grasses with deep roots

• Ultisols 

  • L. Ultimus, last

  • Weathering of clays + leaching of base cations

  • Old land surfaces in moist warm climates 

  • B horizon with <35% base cations 

  • FOund on land surfaces that have been recently exposed - hillsides 

  • Found predominantly in southeastern us 

• Spodosols 

  • Gk, spodos, wood ash

  • Intensive acid leaching of coarse textured parent material 

  • Diagnostic horizon : spodic horizon - the illuvial accumulation of Fe,Al oxides and/or organic matter

  • Often overlain by E horizon

  • Often in forests because of all of the plant material that lives on the topsoil

  • Spodosols do derive their name from wood ash, but the E horizon is not diagnostic of the spodosol, it is actually the Bh/Bs 

• Oxisols 

  • Fr, Oxide - oxide

  • Most highly weathered soils in the taxonomy 

  • Currently or historically humid and warm

  • Diagnostic horizon Bo

  • Epipedon : ochric or umbric

  • Usually uniform subsurface

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Soil architecture & physical properties

•  Soil color

  • Soil color is influenced by three factors

    •  Soil moisture

    • Soil organic matter

    •  Soil mineral composition:

    •  Calcite and soluble salts

    •  Manganese oxides

    •  Iron oxides, and their oxidation states

  • Soil is darker if 

    • In a wetter state 

    • Or higehr in SOM

  • Soil calcium or salts - lighter color 

    • A Bk or calcic horzion formes from the illuvial accumulation of calcium carbonates

    • Redox reactions

  • Color of iron is modified by soil water status

    • S oil water status 

      • - drier more oxidizing environment precense of oxidised iron 

      • Wetter more reducing environment precense of reduced iron or loss or ifon grayish 

    • Things such as bus burrows, cause Macropores  that can get oxidized, retained higher water status in past and now have 

•  Soil texture = size of mineral particles in soil

  • Soil texture triangle 

• The soil with more fine particles have a greater soil surface area than soils with coarser particles

• Assessing texture in lab - using a hydrometer which has a weight and ruler which shows how soil particles are suspended in water 

• Assessing soil texture in field using fingers and hands 

•  Soil architecture, soil structure = the arrangement of particles in soil

  • Asseesion soil texture 

2/5/25

Bulk density and particle density - concept and calculation 

• Density of a single chocolate candy = 1

• Density of jar of chocolate candy >1 or <1 - less than one because solid particles have air in between them 

• Density of soil solids = particle density Dp or ⍴p 

• Density of soil inclusive of pore space = Bulk density Db or ⍴b

• Bulk density measurements 

  • Requires sampling the mass of a precisely defined volume of soil 

  • Vertical soil core from surface

  • g dry soil/cm3 core volume = Bulk density, g / cm3

  • g/cm3 = Mg/m3

• Bulk density calculations 

  • Given a core volume of 98.17 cm ^3

    • Calculated from core radius 2.5cm and core height of 5cm and a volume of cylinder equation 𝜋r2h

    • And a soil sample dry mass within the core of 128.3 g,

• Calculation of soil mass per area 

  • What is the mass of soil the 0-15cm layer in a hectare, if the bulk density is 1.21 Mg/M^3?

  • (1.21Mg/m^3) x (10,000m^2/ha)x 15m = 1,815 Mg/ha

• Variability in bulk density across soils 

  • BD increases with lower SOM higher and 

  • Bd generally increases with depth, in part due to decreases in organic matter, also weight of overlying layers

• Relationship between bulk density and plant growth is generally negative 

  • Soils with lower BD have : 

    • More pore space for water storage and air movement

    • Less resistance to root elongation 

    • Are corrected with higher SOM

    • When plants arent able to carry out their root formation it can result in lower biomass, especially when bulk density is high they have lower organic matter 

• Bulk density responds to foot traffic 

  • Ex: a campground

• RIsks and rationale - tillage operations 

  • Prepare seedbed 

  • Incorporate residue 

  • Control weeds

  • Loosen soil (reduce BD - in short term in tilled depths)

• Subsurface increase in bulk density due to machinery : a plough pan 

  • Wider wheel has less deep but wider compaction 

  • Overcoming a plough pan: subsoiling, cover crops

• Vulnerability to compaction 

• Bulk density - an imperfect measure of soil resistance encountered by roots 

  • A dry soil is generally a hard soil

• Mechanical Impedance - a less imperfect measure of root resistance 

  • AKA penetration resistance or soil strength 

• Penetrometer measurements 

• Calculating soil porosity from BD and particle density

• Soil pores differ in their:

  • Diameter 

    • Macropores > 0.08mm > micropores

  • COnnectivity 

    • Shown at left with yellow pores representing connected pores 

    • here , horizontal pores not connected 

  • Formation and function 

    • Roots and fauna can create macropores

    • MIcropores retain water after drainage; transmit air form soil surface 

• Tillage increases proportion of soil pore volume in macropores 

• Further physical properties of soil 

  • Atterberg limits and the coefficient of linear extensibilty (COLE)

  • Atteberg limits are internationally recognized for some soil classification schemes

  • And for defining solid for their engineering use 

• SHrink/ swells in vertisols 

  • A vertisols in texas high degree of swelling can impede infiltration in wet vertisols

• Atterberg LIMITS 

  • As you add more water the combined mass of soil plus water gets larger obviously 

  • Shrinkage limit

  • PLastic limit

  • Liquid limit

• Compression and proctor test 

  • Known applied force 

  • Column of moist soil

  • Porpous stones on either end 

  • Drop hammer and compacted soil at known water content 

• Gravimetric, Volumetric, energetic 

  • WIll be expressed in volume of water +volume of soil 

• Properties of water 

  • Cohesion - attraction of water molecules to each other 

  • Adhesion - attraction of water molecules to solid surfaces 

  • Structure of water molecule allows for 

Leads to CAPILLARY ACTION

• Activity of capillary in soil  

• Soil in arid environment sometimes have salts that were drawn from below ground that make it impossible for plants to grow there

• Place glass tube in tub of water, surface of glass tube attracts water, forces of adhesion

• Forms meniscus 

• Inversely proportional to the pressure on the surface of the liquid 

• Meniscus will go opposite way if there is a waxy surface 

• Capillarity 

• Can happen over a longer period of time in a finer texture soil

• Gravitational potential of water  

  • Water above reference point 

  • Vs water at reference point

  • Increase in potential energy  in between, arrow pointing up

• Osmotic potential of water 

  • Pure water with no solutes has a 0kPa

  • Meanwhile a solution with a little solute has a -100 kPa

  • Lots of solute will have -200kPA

  • Water always needs to move from higher to lower potential 

• Matric Potential 

  • All of soil pores are 100% occupied by water

  • Downward motion of draining will occur 

  • Some amount of water held between saturation

  • Remaining water is held against the force of gravity

  • what is capacity of a field to hold water against the force of gravity - force capacity 

  • Evaporation - reducing thickness of water films in the soil and getting them closer to soil 

  • Still water in soil plants cant extract— Unavailable water

  • Most tightly bound water - hygroscopic water 

    • Boil off all water, but add water by puting it in a humid room 

  • 0 - Highest water matric potential a sample can have, can only get negative

  • Water held between  field capacity and hygroscopic coefficient capillary water 

  • Rules of thumb for defining these

• At field capacity, air can be introduced into pore spaces  (not shown here (

• Water retention curve 

  • At negative kPa

  • Why is kPa negative??

    • Because water always need to move from high to low potential, so its decreasing in potential 

    • Because water is decreasing in water content and that is the number that is going down 

    • LESS likely to move because the water adhesion is stronger 

  • Volume of moisture available to plants is between between  points B and C = between field capacity and permanent wilting point 

  • Dotted lines = energetic states of water 

• The water retention curve WATCH OUT!!

  • Can be displayed with any orientation 

  • MAtric potential is reporte din many units

  • kPa, hPa, Mpa

  • Bars

  • Cm or mm of water

  • Mm of mercury 

• Hysteresis 

  • Patterns are manifested in one direction of change 

  • Water is drawn up  by narrow pores but capillary rise ceases when pore widens

  • Drying occurs when large pore remains full because of capillary attraction in narrow pore above

• Points in soil retention curve will be different depending on the type of soil 

• Use of pressure plates to measure water content at known water potentials 

  • You purchase a soil water sensor and install it in a greenhouse pot with abeautiful begonia in it

  • Sensor reads volumetric water content, and you calculate that there are 50g of water in pot, plant looks healthy 

  • You conclude that after the pot lost 50g water it will be time to water the begonia again

  • Will your begonia be ok?

  • NO because if all 50 g of water in the plant there will be none for the plant, you would want to water it again instead before it gets to wilting point 

• CAlculating plant - available water in soil profile

• Available water holding capacity (horizon_ = (Gravimetric water (fc) gravimettic water (wp)) x Db/Dwx depth  

  • How much water might be lost in soil in a temperate climate 

    • Even if more water is leaving through evaporation or groundwater, lots of water is coming back in as well through rain or streams 

  • Increasing SOM makes it so that more water is available 

  • Feasible  increase in OM with long term cover cropping or perennial forages integrated into annual grain system represented by width of green box 

• Upper 20 cm of soil as upper land management with organic matter 

• Organic matter only affects top 20 Cm

• Water infiltration\

  • Expressed as linear rate

  • Length (of water) / time

  • Important for hydrologic cycle

  • Measurement about environment an incorporates slope, texture and aggregation + soil features

  • Measured with double ring infiltromete

    • i= Infiltration rate

    • Q - volume of water infiltrating (M3)

    • A- area of soil surface (m2)

    • T = time

• Saturated hydraulic conductivity (Ksat) 

  • Darcys law describes quantity of water (Q) per time t that flows through column in figure 5.19

  • Where is the change in water potential between either ends of length L 

  • You want to know potential energy gravitational, surface area, and amount of water it can hold 

  • Interested in quantity of water moving through clay at a point 

  • We can use this to calculate the quantity of water moving through soil over time 

• One way of visualizing conductivity./ water content over time

• Texture and ksat

  • A clayey soil will have lower/smaller ## 

  • Sandy will have higher as it will be faster  

• Macropores and cracks between clay → nonuniform water movement (aka preferential flow) → transport of nutrients of contaminants >> expectations from K sat 

  • Use dye to measure this to see where the water moves the most

• Unsaturated hydraulic conductivity 

  • Most frequent type of water movement in soil

  • Primarily driven by difference sin matric potential

  • Always occurs from larger to smaller pores

  • Onec water potential is negative, macropores have drained out 

• Subsurface increase ein bulk density due to machinery: plow pan  

  • DIfference in soil texture can prevent the movement in soil 

  • Water movement in stratified soils 

    • Coarser layer of stratification can inhibit water movement 

    • Water not moving from loam to gravel 

    • Water movement in stratified soil 

2/12/24

Soils + the hydrologic cycle 

1. Water balance 

   1. SS = P - ET - D

   2. Evapotranspiration = evaporation + transpiration 

   3. Transpiration - loss of water from plants such as trees + grasses 

   4. Evaporation : loss of water from water bodies and land surface 

   5. Water balance over a year 

      1. Precipitation  > ET surplus can go to soil storage groundwater recharge runoff 

      2. ET> Precipitation Drawing down stores soil water
         
         

      3. Water balance over a year in an arid environment

      4. This is because the ET is pushing up against precipitation, no opportunity for excess precipitation

   6. Potential evapotranspiration

      1. Amount of water respired from a well watered, densely vegetated system

      2. Actual ET may not reach PET - because systems are not always well watered 

      3. Estimation techniques often incorporate multiple components of ecosystems (radiation, temp, wind, and atmospheric pressure)

Soil aeration 

The process by which air in the soil is replaced by air in the atmosphere 

• A well aerated soil the soil air is similar in composition to atmosphere above and poorly aerated contain more CO2 and less O2

• Soil aration in terms of gaseous composition of soil air 

• Soil aeration primarily controlled by 

  • Soil water content

  • Soil mnacroporosity 

  • Rate of O2 consumption in the soil 

• Influence of water on soil aeration

  • Soil water reduces soil aration

  • Because rate of O2 diffusion through water is many times slower than the rate of O2 diffusion through air

• Water filled pore space

  • % water filled pore space = volume of soil water / volume of soil pores

  • Soil is saturated when water filled pore space = 100%

  • R

• Rate of O2 consumption of soils

  • Micorbial activity involves microbial respiration which consumes O2 and produces CO2

  • Microbial activity increases with temp, up to a maximum 

  • Therefore, rate of O2 consumption increases with temp 

• Aerobic soil = has oxygen

• Anaerobic soil = lacks oxygen 

• Wetland soils 

  • Wetland soils are water saturated for prolonged periods, when soil temperatures and other conditions are such that plants and microbes can grow and remove oxygen, thereby assuring anaerobic conditions

  • Wetlands have hydric soils 

    • There are often Histosols 

  • PLant adaptation to waterlogged environments aerenchyma

    • Aerenchyma: large intracellular structures (pore spaces) which extend through the entire plant and allow for storage and transport if gas to submerged roots 

• CO2 in soil air 

  • soil CO2 concentrations are 

    • A. Higher in June than in November

    • B. Lower in June than in November

    • C. The same between June and November Range

  • Rasnge of possible soil temp and their implications for soil processes 

  • Daily variations in air temp near earth's surface is controlled mainly by the input of energy from the sun (yellow) and output of energy form the surface (blue)

  • Soil temp - dinural cycles 

    • Huge range near surface

      •  At 0.5 cm, > 20 C range

      • Max. temperature ~ 2pm

    • Dampened and delayed with depth

      •  At 10 cm, < 6 C range

      •  Max. temperature ~ 6pm

      •  Negligible diurnal cycle at 80cm

  • Soil temp - seasonal cycles 

    • Soil temps fluctuate more at surface than at depth 

2/19./24

 ALbedo  - proportion of radiation that is reflected by a surface 

• High albedo, low albedo

• Bare soil generally has a lower albedo (absorbs more heat  than a soil with crop residue

• Water will be cooler due to specific heat capacity 

• Specifc heat capacity: the amount of energy required to  raise the temp of a unit of a substance by 1 degree C 

• Specific heat capacity of water and sand are different

• A dry soil warms up easier than wet soil 

  • Due to higher specific heat capacity of water compared to soil minerals 

  • Soil temp in different tillage systems

2/22/24

Soil colliods - Organic and inorganic matter with very small particle size and a correspondingly large surface area per unit of mass 

• Sand silt clay are sometimes called soil separates 

• Soil texture is sometimes called soil particle size distribution

• Soils with fine particles have a greater soil surface area than soils with coarser particles 

• Crystalline 

  • Denotes a definite chemical compositions with planner surfaces and regular angles 

  • Atomic arrangement of quartz shows planar surfaces and regular angles

  • However crystalline silicate clays in soil are not formed from disintegration of large crystals into smaller crystals

  • Crystalline silicare clays are among new minerals  - pedogenic clay s

• SOil colloids, including crystalline silicate clays contribute enormously to soils cation exchange capacity (CEC)

  • In cation exchange, cations absorbed to negatively charged clays exchange with cations in soil solution

  • Basic structural components of silicate clay

• Tetrahedral and octahedral sheets stack in different configurations in the different types of crystalline silicate clays 

  • 1:1 tetra to octa hedral 

  • A loose metaphor 1:1 clays are a stack of break and peanutbutter, low filling diversity 

  • 2:1 tetra to octa 

  • 2:1 clays are a sandwich with lots of fillings   

• Different layer structures of silicate clays

• Biotite and muscovite micas are primary minerals, here we discuss secondary minerals also called micas

Crystalline silicate clays in context 

• Kaolinite - white gold - in industrial uses 

  • Minimal shrink, preferred fr ceramics

  • Iron impurities make it red

• Expanding 2:1 clays - smectite

  • Gives vertisols their shrink- swell 

  • Have industrial applications

  • Where swelling when wet is needed to create seal

NON crystalline silicate clays 

• Allophane is a non crystalline silicate clay  composed of Si, Al and O atoms, not arranged in crystalline sheets

  • Primary constituent of volcanic soils (andisols)

• Processes leading to soil charge

  • Constant charge due to isomorphic substitution

    • The process of replacing one structural cation for  another of similar size 

    • Net charge difference is -2 from a Si +4 to Mg2+

    • Often in soil cations are replaced with less positive cation, leading to net negative charge 

  • pH dependent change

2/26/25

Soil colloids 2 

• Review from last cass, what makes a soil colloid a soil colloid 

  •  Organic and inorganic matter with very small particle size and a correspondingly large surface area per unit of mass 

• WHat is a crystalline silicate clay 

  • Denotes a definite chemical compositions with planner surfaces and regular angles 

  • Atomic arrangement of quartz shows planar surfaces and regular angles

  • However crystalline silicate clays in soil are not formed from disintegration of large crystals into smaller crystals

• What features distinguish the types of crystalline silicate clay 

• Iron and alluminum oxides 

  • Here showing Gibbsite  

    • An aluminum oxide clay common in highly weathered soils

  • Octahedral sheets hydrogen bonded together 

  • Other oxide- type clays can have iron instead of aluminum, or be less crystalline structure 

• Organic colloids 

  • Also known as soil organic matter

  • Non crystalline structure 

  • -OH hydroxl groups 

• What happened to the dyes - yellow is more negative and bleu is more positive so blue sticks to the soil!!!!

• Processes leading to soil charge 

  • Constant charge - due to isomorphic substitution 

  • pH-dependent charge 

  • “Such as substitution [isomoprhic; reduction in charge ] commonly occurs in aluminum dominated dioctahedral sheets.”t

• Another view of isomorphic substitution 

  • Process through which structural cation and shapes are exchanged with similar cation that leads to a net negative charge 

• Processes leading to soil charge 

  • pH-dependent charge 

  • Hydroxl (-OH) functional groups exist on the edged of inorganic colloids and organic colloids alike 

• We can consider PH dependent charge by imagining the hydroxl group on the edges of clays and on organic compounds as a 2 car garage 

  • House is the oxygen atom 

  • Cars are hydrogen ions 

  • PH as a reflection of hydrogen ion concentration in  a substance 

  • Decrease in soil ph is like a football game happening in the neighborehood

  • WHen there is 2 the charge becomes +1

• Increase in soil ph is everyone is gone, charge becomes -1

• More acidic - low ph - positive charge - greater anion exchange capacity 

• More alkaline - less acidic - high ph - more negative - greater ion exchange capacity 

• When we sum exchange sites in soil, we report units of charge per mass (soil or colloid) 

  • For CEC, the sum is of negative charges 

  • PH- dependent negative charge increases as soil pH increases although degree varies with soil colloid 

  • As a function of soil ph

• Key point 

  • Weathering of clays follows a general trend in which: 

    • 2:1 clays weather into 

    • 1:1 clYS WHICH WEATHER into 

    • Fe and Al oxides

  • Driven by leeching of silica and cations

  • Constant charge of soil colloid decreases with weathering →

  • Princinples of CEC that contribut to low CEC in southeastern US

  • Highly weathered clays developed under warm humic climate

  • ALso 

  • Lower organic matter high decomposition rates

  • More acidic soils → ph dependent charge leads to anion exchange capacity 

1. 4 rules gocerning cation exchange 

   1. 1. Reversabilty 

      1. WHat goes on may come off 

   2. 2. Charge equivalence 

      1. One +1 cation for another +1 cation or two +1 cations or one +2 cation etc

   3. 3. Ratio Law

      1. The ratio of two different cations in soil solution will equilibriate with those absorbed to exchange complex

   4. 4. Cation selectivity 

      1. SOme cations are held more tightly on exchange complex than other →

      2. The view of cations floating in a solution by themselves is a simplification because cations are usually hydrated

      3. hydrated radius describes the effective size of cation in solution 

2. Measuring cation exchange capacity 

   1. Additon of NH 4 to soil 

   2. Replaces other action son the exchange matric these cations are leached into beaker and excess NH is removed with organic solvent 

   3. Very high concentration K+ solution is used to replace and leach absorbed NH4

      1. NH4 and K+ have similar hydrated radii so ratio law comes into effect

   4. Amount of NH4 leached from osil can then be quantified representing total negative charges )CEC) fron soil 

   5. WHy do we use NH 4 to measure cation exchange 

      1. Small hydrated radius makes it more likely to:

         1. Replace larger more hydrated cations

         2. Not be displaces by larger more hydrated cations

         3. NH4 in solution can be easily measured

2/28/24

Mesuring cation exchange 

1. Additon of NH 4 to soil 

2. Replaces other action son the exchange matric these cations are leached into beaker and excess NH is removed with organic solvent 

3. Very high concentration K+ solution is used to replace and leach absorbed NH4

   1. NH4 and K+ have similar hydrated radii so ratio law comes into effect

4. Amount of NH4 leached from osil can then be quantified representing total negative charges )CEC) fron soil 

5. WHy do we use NH 4 to measure cation exchange 

   1. Small hydrated radius makes it more likely to:

      1. Replace larger more hydrated cations

      2. Not be displaces by larger more hydrated cations

      3. NH4 in solution can be easily measured

Soil organic carbon increases soil CECm and does this to greater extent in high pH soils 

Soild higher in CEC - whether due to organic colloids, inorganic colloids, or both- have greater capacity to prevent nutrients cations from leaching

SOIL ACIDITY 

• Features of a log scale

  • 1 each gardation of “1” on a pH scale represents a 10 fold difference in H+ ion concentrations

  • 2. Absolute change in H+ iron concentration for 1 unit pH change is much greater on the acidic side than on alkaline side of scale

  • PH range of soils and other materials 

• To understand how acidity develops over time, where does it come from?

  • Sources of soil H+ in soil 

    • Dissociation of carbonic acid from CO2 

      • Process if molecules splitting apart 

      • High concentrations of CO2 in soil are dissolve into soil solution which then forms carbonic acid, when then dissociates to bicarbonate and H+

    • DIssociation of acidic functional groups on organic matter (from plants)

      • Functional groups = specific groups of atoms within molecules that have their own characteristic properties regardless of the other atoms present in a molecule

    • Oxidation of ammonium (NH4) to nitrate (NO3-) releases two H+

      • Microbes oxidize NH4 as an energy source through process known as nitrification

      • This contributes to acidification of ammonium based fertilizers

    • Oxidation of sulfer

      • Either through organic matter that contains SH groups

      • Or through pyric oxidation FeS2

    • Input of acids in precipitation

      • Sulfur dioxide (SO2) and Nitrogen oxifes (NO) are released from fossil fuel combustion 

      • Undergo atmospheric reaction to form acid rain

      • When dissolved in rainwater and dissociate

      • Generating acidity 

    • Plant roots taking up cations then releasing H+ to maintain their charge balance

      • Plant roots cells need to maintain a charge balance across their cell membranes

      • Therefore if one positive charge (nutrient cation) goes in, one positive charge (H+ or other cation must go out

      • Plant roots taking up anions, then releasing bicarbonate HCO3 to maintain charge balance

      • Reduction of nitrate to nitrogen gas ( denitrification)

• Types of soil acidity 

  • Active: in solution

  • Exchangeable: held ner colloid surfaces

  • Residual: tightly bound to colloid surfaces 

  • Active acidity is a very small amount of acidity compared to exchangeable and residual acidity. 

• Acid cations = cations that generate and H+ aqueous solution in soil, thes are H+ and Al3+

  • AL3+ generates H+ by hydrolyzing water and combining with resulting OH 0 

  • One AL3+ can erelase up to three H+ ions 

Soil pH will decrease but to a lesser extent of that of water if you ad 3cMol of acid to soil on pH

• Because soil has a buffering capacity  

• Buffering: An addition of acidity will cause more acidity to move to exchangeable acidity in soil colloids so the addition of acidity is not fully reflected in active measured acidity

• Mechanisms of pH buffering

  • Protonation and deprotonation of organic matter functional groups (R-OH)

    • Gaining or giving protons H+

  • Protonation and deprotonation of pH- dependent charge sites 

  • Cation exchange reactions

  • Reactions of aluminum and carbonates 

• Soils become acidic when 

  • H+ ions are added to soil

  • Thes H+ solutions exchange with nonacid cations Ca2_ Mg 2+, K+ Na+ held on colloids

  • Noncaid cations are leached way (bc they travel with anions)

    • In arid regions nonacid cations remain in soil and re-exchange with acid cations, preventing a drop in pH level 

    • An acidic soil has an exchange complex dominated by acid cations

  • WHat about this soil propoerties might be different 

    • Organic matter of inorganic colloids could influence buffering capacity which is why they are different, orange is sandier

    • L

• L

Acidic organic material

High rainfall

Parent material low in nonacidc cations

Sandy soiuls (low buffering capacity)

3/3/25

• Hydration of cations influences their effective radii, and therefore how easily they are replaced in a cation exchange 

  • Larger hydrated  cations have weaker bonds and therefore are replaced easily 

• Sources of H+

  • Respiration- dissociation of carbonic acid 

  • Decomposition of organic matter

  • Oxidation of ammonium based fertilizers 

• Acid saturation 

  • Recall percent base saturation 

  • We calculate acid saturation using same approach 

  • Acidity throughout the soil profile 

• Given The sources of H+, which pH graph would you predict is more likely found in a humid climate 

  • Surface of soil is more subject to plant matter composition and weathering

  • More acidic in the higher soil and less acidic in the lower soil 

  • Solubility of aluminum declines rapidly at soil pH above ~5.0-5.5

• Inputs of acidic organic material mobilize AL3+

  • Fewer H+ sources; Al precipitates, contributing to formation of Bs horizon 

Soil pH and crops 

• Some crops prefer acidic soils, some prefer neutral, some prefer alkaline soils 

• Justus von liebig's law of the minimum published in 1873

• “If one growth factor/nutrient is deficient. Plant growth is limited, even if all other vital factors / nutrients are adequate…. Plant growth is improved by increasing the supply of the deficient factor /nutrient “

• Modified truog diagram which purports to show nutrient availability across the range of soil pH:
  Limitations:

  • Width of band is not actual amount of nutrient 

  • Even at widest part of band, nutrient may not be non limiting for plant 

  • Even at narrowest part of band nutrient may not limit plant growth 

  • Diagram implies that optimal soil pH is about 6.5, but crops can be highly productive outside this range

  • Even if topsoil pH is low, low ca, plants may uptake Ca from subsoils

• Limitations; more recent 

  • Plant roots and soil particles both have pH dependent charges and nutrient availability is mediated by both plant and soil charge 

  • Evidence of plant uptake and colloid resorption following apparently opposite patterns 

    • pH conditions with most absorption of colloid are same as pH conditions that make it best for plant uptake 

  • Many unknown remain regarding role of pH in nutrient availability 

• Contrary to statement that remain popular in agronomic texts the soil pH cannot be used to predict or estimate plant nutrient availability 

• What is well established regarding mechanisms of crop preference for soil pH labels 

  • Nutrient mineralization increases with pJ 

    • More in N cycling later classes

  • Aluminum toxicity at low pH

• Aluminum toxicity at low pH

  • At pH <5.5 aluminum is in the Al3+ form and competes with the essential nutrients like Ca 2+ Mg2+_ and K+ for negatively charged exchange sites

  • Plants can experience toxicity form taking up Al3+ and trying to use it in palace of Ca2+

  • Aluminum takes hydrogen and generates hydrogen irons and lowers pH 

• Aluminum takes hydrogen and generates hydrogen irons and lowers pH

Why do we lime soils

• We lime soils because it helps us to neutralize soil acidity and increase soil pH

  • Acid cations in lime can replace cations in solution of soil

• The greater the buffering capacity of soil the more lime is needed to realize the pH

• Effect of limiting in raising pH is greatest in horizon is application

  • Evenbut dilute increase in pH

• Liming generally needs to be repeated over time

  • because water and effects can change the liming effects

• Alkaline = pH above 7 = more OH- ions

  • Alkaline soils are mostly found in arid reagions

  • Arid regions have limited sources of H+ due ot low biological activity

  • Arid regions experience limited leaching of Ca2+, Mg 2+ K+ and Na+

• Features of soils in arid regions

  • Water limitation

    • Potential evapotranspiration > precipitation

    • PET - potential could be greater than what is actually evaporating

    • In arid environments theres a larger demand for water in environment

    • demand for water is greater than water that is going into soil s

  • Island of fertility

    • Plants protect soil from erosion and promote water infiltration and storage

    • Grazing animals concentrate manure to grazed areas providing more organic matter

    • leading to fertility to suppport more plant growth (start over at protection of soil )

  • Used for grazing

    • Requires less water input than rainfed crops

  • In some areas people irrigate soils in arid regions which can increase the risk of soil salinization

Process of soils accumulating excess salt= soil salinization

• Salt affected soils:

  • ~7% of earths land area,

  • 23% of cultivates area

  • 50% of irrigated area

  • Can have an extremely bad effect on food

• Alkaline soils: pH above 7

• Saline soil: high concentration of soluble salts

  • in exchess of 4 deciSiements per meter

  • Salts commonly found in soils and natural water and their solubilty (mmolc L^-1)

  • Key point: carbonate and bicarbonate based salts are usually lower in solubilty than sulfate and chloride based salts

  • We can understand related process of saline lake formation ex: great salt lake

    • Due to inputs of water with dissolved salts

    • evaporation of water

    • absence of exit pathways for salts

    • repeat

  • Formation of saline soils through the addition of irrigation waer

    • Saline irrigated soils form from:

      • Inputs of water with dissolved salts

      • evapotranspiration of water

      • Absence of exit pathways for salts

      • repetition of this process

    • Even freshwater has small amounts of dissolved slats which are concentrated in the soil

  • Measuring salinity

    • Separately quantifying all the salts is too labor intensive and expensive

    • Therefore, we rely on bulk quantification of salts through

      • Total dissolved solids (TDS)

      • electrical conductivity (EC)

• Total dissolved solids extraction process

  • Extraction of dissolved salts in aqueous solution

  • filtration to remove soil particles

  • Evaporation of water (shown in diagram)

  • Weighing of remaining soilds
    

• Electrical conductivity, principle

  • More rapid than directly quantification of TDS

  • Based on principle of salt water a s a good conductor of electricity

  • More salts in solution —> greater electrical conductivity

• Conductivity, practice

  • Mix distilled water with soil until it flows slightly

  • allow salts to dissolved overnight or half an hour

  • extract solution and measure ec with electrode

  • report ec reported in deciSiemens per meter

    • Describes abilty of soil to conduct electrical current

SODIC SOIL

• The soluble salts are primarily sodium

• Sodic soils are high in sodium as the dissolved salt

  • Higher in sodium because its lower in calcium

  • Soil sodicity can be quantified with the exchangeable sodium percent (ESP) shown here

  • OR with the sodium absorption ration (SAR)

    • SAR= {Na+}/(0.5{Ca2+}+0.5{Mg2+})

• This quadrant of salinity and sodicity

  • Sodic soils can have particularly high pH levels

    • due to reactions of sodium with carbonate and bicarbonate in solution which calcium and magnesium undergo to much lesser extent )

  • AND sodic soils have particularly poor structure

• The charge to hydrated radius of cations influences soil structure

  • Sodium has a slightly smaller hydrated radius than calcium or magnesium but only half of the charge

  • Lets imagine a couple of soil colloid particles van der waals forces can contribute to their aggregation

• Sodic soils - consequences of poor structure

  • Forms a crust almost on top of soils

The charge of hydrated radius of cations influecnes soil structure

• Sodium has slighly smaller hydrated radius than calcium but only half of the charge

  • will increase or decrease soil aggregation?

• Sodic soils

  • COnsequences of poor structure

  • Flocculated (aggregated) vs dispersed strucure, flocculated can allow water to move, disperesed plugs soil pores and impede water movement

• 3 distinct causes of low permeability under sodic conditions

  • Dispersion

    • Clay particles seperate from one another rather than flocculating

  • Slaking

    • Aggregate disruption upon becoming wet —> clogging of soil pores

  • Swelling

    • Sodium enhances swelling expanding 2:1 clays

    • hich relationship would

Which relationship would you expect between ESP and Ksat

• ESP intereferes with Ksat

More ways salts can interfere with plant growth

• Osmotic effects
  

• Water moves from high to lowe

  • Higehr potential in non saline soil solution

  • lower potential in plant root due to solites lowering water potential

  • Water in soil and plant converges in potential

  • making it more difficult for plant rooots to remove water from soil

• Specific ion effects - what they are

  • Like mushroooms - some are harmless and some are deadly

  • Some ions are fine (CA2+ K+)

  • some ions cayse problems (Na+, CL-)

• Specific ion effects:sodium

  • Sodium is a quasi essential element

    • Required for some but not all plants

    • neededby corn, sorghum, and oter tropical grasses

    • Excess sodium in soil can become toxic because Na competes for K+ which is an essential element

• Are all saline soils also sodic soils?

  • False

• Reclamation strategies - saline soils

  • Cannot be reclaimed by chemical amendments, conditioners, or fertilizers

  • Field can only be reclaimed by removing salts from plant root zone

• Opposing goals of irrigation

  • For regular irrigation: just apply enough water limitation on plant growth

  • for removing salts from root zone

    • Apply water in excess of what is needed for crop growth, so salts can move downward through soil profile and out of root zone

Efficacy of leeching

Reclamation strategies - sodic soils

• Application of gypsum - which contains calcium

• calcium replaces sodium held in cation exchange on soil colloids

• then soluble salt, NASO4 is formed, which can be easily leached away

• 
  

Exam review

• Aluminum toxicity

  • Aluminum is positively charged ion that can bind to the cation exchange capacity as soil becomes more acidic and the soil pH decreased

  • Aluminum displaces beneficial nutrients from the CEC

• Cation exchange capacity

  • A soils ability to like exchange cations and how many positively charged ions a soil can hold

  • Expanding 2:1 clays have higher capacities

• Protonation

  • The proces of adding protons (H+) to function groups on soil surfaces, which can change soil pH and charge, this occurs more often in acidic soils

• Alfisols

  • Soil is rich in aluminum and iron

  • Argillic, kandic, or natric horizion

  • found in more wet soils

• Ultisols

  • Strongly weathered acidic soils found in humic regions

  • HIgh in pH and Al3+

  • Found in more temperate areas

You uncover archives of ancient civilization

Instead of 12 soil orders, they group soils into 3 categories based on base saturation

• Low base saturation

• Medium base saturaton

• HIgh base saturation

• Describe extent of soil weathering for each of these three soil orders

• As soils beccome more weathered, base saturation goes down

• so a more sautrated soil will be less weathered.

Mollisols

3/10/25

pH range of soils and other materials 

Soil organisms - grouped by size 

• Macro-organisms  (>2mm) > MESO - organisms (>0.1-2mm) > MICRO organisms (<0.1mm)

• Worms, termites, mice > springtails, mites > tardigrades, nematodes, fungi, bacteria, archaea

• Soil organisms - grouped by metabolism 

  • Metabolic grouping of soil organisms based on source of energy  and carbon 

  • Source of carbon - combined organic carbon - biochemical oxidation 

    • Chemoheterotrophs , all animals, plant roots, fungi, actinomycetes and most bacteria

      • Earthworms, fungi, water bears

  • What are most of these organisms getting their combined organic carbon from?

    • Both chemoheterotrophs and Photoautotrophs 

  • Carbon dioxide or carbonate - solar radiation

    • Photoautotrophs plant shoots, algae, cyanobacteria

• CARBON can be cycled through an intermediate consumer before it is consumed by Chemoheterotroph

• Chemoautotrophs that use carbon dioxide and carbonate

  • Ammonia oxidizers and sulfur oxidizers 

  • Are doing it as an energy source transformation

  • Getting carbon from inorganic sources 

• Trophic levels and energy transfer 

  • Primary consumers in soil 

    • Herbivores : eat live plants

      • Larvae of cane beetle which feeds on living sugarcane plants in all stages of life cycle

    • Detrivores: eat remains of dead plants and microbes on them

    • Saprotrophs: microorganisms that consume detritus, corpses and feces

  • Secondary consumers in soil 

    • Carnivores : eat other animals

    • Microbivores feeder : eat microbes 

      • Protozoa, which graze on soil microbes 

• Trophic levels and energy a( and carbon transfer) of belowground communities 

• Other microbes exist in soil that arent as involved in the soil organic matter 

  • Process of transformation 

• Trophic cascade of aboveground communities 

  • 10% of energy is lost every time 

  • SMall part of period is small itty bitty animals compared to plants as largest energy source