NREM 301 Day 12
• Briefly review Tuesday’s lab – Agricultural Ecosystems • Discuss weathering, soil chemistry/fertility and organic matter • Reminder – Individual paper from Soil Bio- and Toposequences Lab due next Thursday (Oct. 2) Riparian Buffers Can:
1 ) Cut sediment in surface runoff as much as 90% 2 ) Cut nitrogen and phosphorus in runoff by 80% 3 ) Entice and support 5 times as many bird species as row cropped or heavily grazed land 4 ) Allow water to infiltrate 5 times faster than row cropped or heavily grazed land 5 ) Remove up to 90% of ground water nitrate 6 ) Cut streambank erosion by as much as 80% from row cropped or heavily grazed land 7 ) Reach maximum efficiency for sediment removal in as little as 5 years 8 ) Reach maximum nutrient removal efficiency in 10-15 years 9 ) Increase soil organic carbon up to 66% 10 ) Be most effective at upper reaches of a watershed Soil Parent Materials – the raw mineral material soils are developing in.
Rocks and Minerals Deposited in oceans -marine sediment Deposited in lakes ----lacustrine sediment Deposited in streams -alluvium – floodplain, delta terrace, fan ice Deposited by ice ----glacial till --- moraines transport Deposited by water --outwash – alluvium, marine lacustrine Deposited by wind - eolian --- loess, eolian sand, Residual sediment volcanic ash parent material (bedrock weathered Deposited by gravity –colluvium – creep, landslides in place) types of examples of deposits landforms or deposits
Modified from Brady and Weil. 2002. The nature and properties of soils. 13th edition. Prentice Hall. Physical Weathering
Definition: disintegration of rock material into smaller-sized Weathering in fragments. The general mechanism for physical weathering is the establishment of sufficient stress for the rock material to break. Soil Common processes:
1. Expansion
1) Crystallization: freezing water, salt crystal growth Weathering refers 2) Thermal expansion/contraction: differential to the alteration of expansion/contraction of minerals, effects of fire. 3) Unloading rocks and 4) Plant and animal influences (e.g., roots, lichens)
minerals at or 2. Abrasion of material during transport by water, ice, wind, and gravity. near the Earth’s surface. Chemical Weathering
Definition: weathering of rock material that results in a change in chemical composition.
Common processes:
1. Hydrolysis 2. Oxidation/Reduction 3. Hydration 4. Solution
Physical weathering by root action Physical weathering due to water and wind action
Slot Canyon, Zion National Park, Utah Physical weathering – wave abrasion of limestone pebbles, Lake Michigan
Source: Sandor Physical weathering – fire cracked rock, Idaho
Source: Jim Gubbels Weathering till boulder, Sierra Nevada Mountains
Source: Sandor Chemical and physical weathering rind in diorite till boulder, Des Moines Lobe
Source: Sandor Deep (bio-geo- chemical) weathering in bedrock-Ultisol, Georgia
Source: Sandor CommonCommon PrimaryPrimary SilicateSilicate Minerals Minerals Primary minerals, the original minerals of the Earth, are formed at high temperature and/or pressure in igneous and metamorphic rocks. They constitute the majority of sand and silt in soils.
Mineral Composition Si:O Silicate Structure
Quartz Si02 1:2 Tectosilicate (3-dimensional framework)
Feldspar 1:2 Tectosilicate K-feldspar (orthoclase) KAlSi3O8 (Si or Al: O)
Plagioclase NaAlSi O 3 8
CaAl2Si2O8
Mafic Minerals:
Mica (biotite) Fe, Mg 2:5 Phyllosilicate aluminosilicates (layer silicate)
Amphibole (hornblende) Fe, Mg, Ca 4:11 Inosilicate aluminosilicates (double chain silicate)
Pyroxene (augite) Fe, Mg, Ca 1:3 Inosilicate aluminosilicates (single chain silicate)
Olivine (Fe,Mg)2SiO4 1:4 Nesosilicate (island silicate) Cation Exchange Capacity (CEC) – a key soil fertility property of some clay minerals and humus CEC definition: the amount of exchangeable cations a soil can adsorb. Adsorption refers to the holding of these cations near clay surfaces by electrical attraction.
Negatively charged clay Cation Exchange plant root
exchange
reactions
Cations in the soil water solution Exchangeable cations Plant roots mainly take up nutrient adsorbed to clay surface ions from the soil solution Several plant nutrients occur in soil as cations (positively charged ions), for example Ca2+, Mg2+, K+, Fe2+, Cu2+, Zn2+, and others. Negatively- charged clay and humus particles hold cations in soil, prevent leaching loss of these cations, and make them available for uptake by plants. Origin of Cation Exchange Capacity (CEC) in Clay Minerals • CEC definition: the amount of exchangeable cations that a soil can adsorb. Adsorption refers to the holding of these cations near clay surfaces by electrical attraction. Exchangeable cations Ca2+ K+ tetrahedral sheet • Mainly found in 2:1 clays octahedral sheet tetrahedral sheet Ca2+ K+
• CEC mainly results from process of isomorphous substitution during clay mineral formation. Isomorphous substitution involves the replacement of one element for another inside the clay mineral at the time of formation. Examples of isomorphous substitution: Aluminum (Al3+) substitution for Silicon (Si4+) in tetrahedral sheet. Magnesium (Mg2+) substitution for Aluminum (Al3+) in octahedral sheet. Note in both cases a cation with lower valence replaces one of higher valence, resulting in a net negative charge, or layer charge. This negative charge is offset by the exchangeable cations.
Base saturation – a soil property related to Cation Exchange Capacity and also essential to soil fertility Base saturation % refers to the proportion of base-forming cations (calcium, magnesium, potassium – all major plant nutrients, and sodium) on cation exchange sites. The remaining cation exchange sites are occupied by exchangeable acids (hydrogen and aluminum ions).
2+ 2+ + + Base Saturation % = Ca + Mg + K + Na x 100 CEC Base saturation is positively correlated with pH. Acidic, highly weathered soils such as Ultisols and Oxisols have lower base saturation (and lower CEC) than less weathered, less acidic soils such as Mollisols and Alfisols. CEC Sites (%)
Source: Birkeland 1999 Soil pH Range of Soil pH
Relative concentration - of H+ or OH
Acid Neutral Alkaline
pH345678910
acid sulfate soils leached soils many fertile soils calcareous soil sodic soil lemon juice pure water soap
Source: Jenny. 1980. The Soil Resource q
Effect of Parent Material on Soils and Ecosystems Example from Sierra Nevada Mountains, California (Jenny, 1980)
Igneous Rock Parent Material Soil Properties Silicic Rocks Mafic Rocks
Organic Carbon % 1.74 2.88
Total Nitrogen % 0.074 0.121
Clay % 12 21
Exchangeable 511
Bases (cmol+/kg) Soils Contain Organic Matter
Living plant tissue Litter Soil organisms Coarse debris Plant exudates Humus
Soil is dynamic & full of life! Root Tip & Rhizosphere Ectomycorrhizae Special Soil Fungi Mycorrhizal Fungi Mycorrhizae = symbiosis between fungi and root.
Fungi receives carbon from plant, plant gets a 10-100X increase in absorbing root surface area. Ectomycorrhizae Basidiomycetes & Ascomycetes * spores wind & water dispersed * 2,100 species of fungi in NA * most conifers, willow, aspen, oak, hickory Endomycorrhizae (VA) Phycomycetes – spores below ground * most widespread, associate with * most plant families including crops VA Mycorrhizae * most deciduous trees (P 10 – Handout) Group Activity
Identify 6 major kinds of OM that are found in soil.
Use the pictures to help identify the different kinds. Types of Soil Organic Matter
1. Living tissues of plants & symbionts
2. Soil biomass – living organisms other than plants (microbes, invertebrates – ants, beetles, earthworms, etc.) 3. Exudates and leachates – biochemicals from living & dead tissues – provide energy
4. Litter – fresh or partly composed – above & below ground light fraction – easily decomposed (L & F) heavy fraction - humic material slow to decompose 5. Coarse woody debris – larger pieces of wood - > 1 in diam water storage & habitat for meso & micro-fauna 6. Humus – mostly synthesized OM released by microbes &
invertebrates; 80-90% of SOM; major CO2 storage.
O Horizons – Forest Floor
L – litter (Oi) F – fermentation (Oe) H – humus (Oa)
Kinds of FF’s
Mor – Oi (L) Oe (F) Conifer Oa (H) Acid
Mull – Oi (L) Low C/N Oe (F)? Deciduous Basic
Moder – Oi (L) Oe (F) Oa (H)? Mor Forest Floor Conifer/Acid Slow Decomposition Clear Break Between FF & Soil
Oi (L)
Oe (F)
Oa (H)
Mineral soil Mull Forest Floor Deciduous Basic/Low C/N
Oi (L)
No Oe & Oa
Incorporated Into A No Break Between FF & Mineral Soil Bogs 1. Northern or high elevation climates 2. Water source - precipitation 3. Anaerobic water 4. Low pH < 5 5. Slows decomposition 6. Sphagnum moss
Histisol Organic Soil
Fens 1. Similar locations 2. Water source is groundwater or stream 3. Higher pH 4. More nutrients 5. More plant diversity Fall is here and the leaves are falling off of the trees Group Activity These leaves play an important role in maintaining the organic matter in the soil. How do you think they become part of the OM?
Please use this figure to expand your answer Group Activity
A) What % of the aspen leaves is water?
B) What % of the aspen leaves are C, H, O and ash?
Lignins & phenolic compounds
C) Rank the compounds from Cellulose fastest decomposition to Sugars, starches & simple proteins slowest. Hemicellulose Fats, waxes, etc. Crude proteins Page 31 Soil & Plant Handout
Composition of typical green plant material
Sugars, starches & simple proteins Rapid decomposition Crude proteins Hemicellulose Cellulose Fats, waxes, etc. Lignins & phenolic compounds Slow decomposition Group Activity
A) What is meant by the term detrital food web?
B) How is this food web similar, different from the traditional terrestrial food web?
C) What are the three major steps of decomposition? Soil Food Web
Decomposition
1. Oxidized to water & CO2
2. Heat energy
3. Nutrients released (mineralized)
4. Resistant compounds produced by organisms C/N
Dry Plant OM 42% = C 1-2% = N
1. Microbes need 8 C for 1N to build cells
2. Need 16 C for Rs
3. Need C/N = 24/1
C/N = 30:1 4. If OM > 24:1 C/N = 120:1 microbes take N from NO3 in soil C/N = 300:1
Temperature & Moisture Influences on SOM
What does this figure show?
Higher temperature decreases SOM • faster decomposition • higher respiration
Higher moisture increases SOM • more production of OM • possibly slower decomposition
Page 29 Soil & Plant Handout Soil pH Microbial activity & Nutrient availability
What is the effect of pH on the decomposition? Check the impact on fungi and bacteria Thus ends our in-depth discussion of soils – Questions??
But don’t forget these processes as you continue to discuss forest ecology Soil – The Basic Natural Resource (CliPROT) Molly McGovern, INHF