Note: Feature B is waxy in appearance (not evident in the photo).

Transcription

1 NREM Day 9 Quiz Answers from last Thursday up later Wrap up discussion on soil texture and porosity. Discuss weathering and soil chemistry/fertility Lab today Identifying Soil Bio- and Toposequences. NOTE: Individual id paper from today s lab due in two weeks (October 6)

2 A B Individual 1 C a) Match the letters with numbers A3, B1, C2 For the following rank letters from high to low & give brief Why b) Organic matter content A, C, B (prairie grasses have deeper roots and put more organic matter into the soil) c) Amount of erosion occurring B, C, A (little structure, surface litter, or root matter in the crop field soil) d) Degree of structure development in the surface horizon A, C, B (More roots and organic matter lead to better structure)

3 1. What are these two soil features? 2. What causes them? Individual 2 A Mottles, caused by oxdiation and reduction of iron due to a fluctuation water table B Clay coatings, caused by illuviation of clay Note: Feature B is waxy in appearance (not evident in the photo).

4 Individual 3 Name the five soil forming factors Soils = f(cliprot) Climate Parent Material Relief (or Topography) Organisms Time

5 Individual 4 Last Individual Question Define: a) Aspect The cardinal direction that the slope faces. b) Bt horizon A subsurface horizon that has received illuviated i materials from upper horizons, particularly l clays. c) Colluvium Parent material deposited by gravity. d) Eluviation Leaching or washing out of one horizon to the next. Commonly happens in E horizons.

6 Group 1 Your classmates sampled soils last year in Montana 1. What slope position are they on? - Backslope 2. Because of the slope position, describe briefly what they might see in terms of soil development and why? Very little soil development; high slopes do not allow materials to rest in place long enough to undergo pedogenesis.

7 Group 2 Last Group Question Sketch the types of horizons and relative thicknesses you would find as time increases (assume temperate forest veg. & all other soil forming factors are equal) A A A O C C Bw E Bt C C 0 Time (years) 1,000 s

8 Soil Texture Soil Texture Sand Sand Silt Silt Clay Clay Holding Holding Low Low Medium Medium High High water water Aeration Aeration Good Good Medium Medium Poor Poor OM level OM level Low Low Medium Medium High High Spring Spring Fast Fast Medium Medium Slow Slow warm warm-up up Compact Compact Low Low Medium Medium High High Erosion Erosion Low Low High High Low Low Fertility Fertility Low Low Medium Medium High High Group Group ph ph change change High High Medium Medium Low Low Exercise Exercise

9 Granular Ped a c b d Soil Structure Aggregation of Sand, Silt, Clay & OM Glued together into Peds or Aggregates e f

10 Strength of structure has a role in water movement

11 Porosity and Bulk Density Nikki D Adamo Doolittle Praririe Soil (right) vs. Adjacent Crop Field (left) Bulk Density = Weight of oven dry soil / Volume of whole soil (solids + air space)

12 Strength of structure also has a role in soil erosion Jim Richardson/National Geographic Image Collection

13 Loss of Porosity and Structure by Compaction by large equipment Agricultural Activities Logging Activities

14 What Happens to Soil Structure When - Forest (or Prairie) is replaced by corn & soybeans?

15 Results of Cultivation Structure Destroyed Infiltration rates drop from 3-6 in/hr to in/hr Runoff increases 20-60% Streams carry more water

16 Poor Soil Structure and Trees Porosity reduced Aeration reduced Moisture increased Microbial activity reduced

17 Weathering in Soil Weathering refers to the alteration of rocks and minerals at or near the Earth s surface. Two types: Physical & Chemical

18 Physical Weathering Definition: disintegration of rock material into smaller-sized fragments. The general mechanism for physical weathering is the establishment of sufficient stress for the rock material to break. Common processes: 1. Expansion a) Crystallization: freezing water, salt crystal growth b) Thermal expansion/contraction: ti differential expansion/contraction of minerals, effects of fire. c) Unloading d) Plant and animal influences (e.g., roots, lichens) 2. Abrasion of material during transport by water, ice, wind, g p y,,, and gravity.

19 Soil Parent Materials the raw mineral material soils are developing in. Rocks and Minerals Residual parent material (bedrock weathered in place) ice transport Deposited in oceans -marine sediment Deposited in lakes ----lacustrine sediment Deposited in streams -alluvium floodplain, delta terrace, fan Deposited by ice ----glacial till --- moraines Deposited by water --outwash alluvium, marine lacustrine Deposited by wind - eolian --- loess, eolian sand, sediment volcanic ash Deposited by gravity colluvium creep, landslides types of deposits examples of landforms or deposits Modified from Brady and Weil The nature and properties of soils. 13 th edition. Prentice Hall.

20 Chemical Weathering Definition: weathering of rock material that results in a change in chemical composition. Common processes: 1. Hydration 2. Hydrolysis 3. Oxidation/Reduction 4. Dissolution 5. AidR Acid Reactions (eg. carbonation) 6. Complexation/Chelation

21 1. Hydration: the chemical combination of water with another substance; binding of intact water molecules l to a mineral. Example: Hydration of iron oxide to hydrous oxides Fe 2 O 3 + H 2 O 2FeOOH (same as Fe 2 O 3 *H 2 O) (hematite) (goethite) Produces Red colors Produces Yellow and brown colors 2. Hydrolysis: reaction of minerals with split water molecules, leading to cation displacement. Example: Hydrolysis of feldspar and production of kaolinite clay. 2KAlSi 3 O 8 + 2H + + 9H 2 O Si 2 O 5 Al 2 (OH) 4 + 4H 4 SiO 4 + 2K + (K-feldspar) (kaolinite) (soluble silica/silicic acid) + (potassium ions)

22 3. Oxidation/Reduction: process of substance losing (oxidation) or gaining (reduction) electrons (e-). Example: Oxidation and reduction of iron 2Fe HCO O 2 + 2H 2 O Fe 2 O 3 + 4H 2 CO 3 (iron oxide or hematite, with Fe 3+ ) 4. Dissolution: Water hydrates the cations and anions in a solid until they are dissociated from one another and are completely surrounded by water molecules. Example: Dissolution of salt NaCl Na + + Cl -

23 5. Acid Reactions: Strong or weak acids react with soil minerals to hasten weathering. Example: Carbonation CaCO CO 2 H 2 O Ca 2HCO 3 (Calcium Carbonate + Carbon Dioxide + Water) yields (Calcium + Carbonic Acid) 6. Complexation/Chelation: Formation of metal-organic complexes in which a metal cation (e.g., Fe 3+ or Al 3+ ) becomes part of an organic ring structure. Example: Chelation of iron CH 2 C CH 2 COOH COOH OH + Fe(NO 3 ) 3 COOH citric acid CH 2 C CH 2 COOH COO O Fe + 3HNO 3 COO chelated iron

24 Physical weathering by root action

25 Physical weathering due to water and wind action Slot Canyon, Zion National Park, Utah

26 Physical weathering wave abrasion of limestone pebbles, Lake Michigan Source: Sandor

27 Physical weathering fire cracked rock, Idaho Source: Jim Gubbels

28 Weathering till boulder, Sierra Nevada Mountains Source: Sandor

29 Physical weathering Unloading in granite, Sierra Nevada Mountains

30 Chemical and physical weathering rind in diorite till boulder, Des Moines Lobe Source: Sandor

31 Deep biogeo- chemical weathering in bedrock Ultisol l in Georgia Source: Sandor

32 Common Igneous Rocks Igneous rocks are formed from magma (molten rock)

33 Common Primary Silicate Minerals Primary minerals, the original Common minerals Primary of the Silicate Earth, are Minerals 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 Quartz Si02 1:2 Feldspar 1:2 K-feldspar KAlSi3O8 (Si or Al: (orthoclase) O) Plagioclase NaAlSi3O8 CaAl2Si2O8 Mafic Minerals: Mica (biotite) Fe, Mg aluminosilicates 2:5 Amphibole (hornblende) Fe, Mg, Ca aluminosilicates 4:11 Pyroxene (augite) Fe, Mg, Ca aluminosilicates 1:3

34 Clay minerals have a layer silicate crystal structure consisting of tetrahedral and octahedral sheets y Clay building blocks: tetrahedron tetrahedral sheet octahedron octahedral sheet Example: 1 layer of 1:1 clay 1 tetrahedral sheet bonded with 1 octahedral sheet

35 Properties of Common Clay Minerals cmol (+) /kg or Kaolinite mostly in highly-weathered, acidic soils like Ultisols and Oxisols and exchangeable cations Smectite mostly in less weathered, base-rich soils like Mollisols l and Alfisolsl and exchangeable cations (Mg 2+ )

36 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 Exchangeable cations adsorbed to clay surface Cations in the soil water solution Plant roots mainly take up nutrient ions from the soil solution Several plant nutrients occur in soil as cations (positively charged ions), for example Ca 2+, Mg 2+, K +, Fe 2+, Cu 2+, Zn 2+, and others. Negativelycharged clay and humus particles hold cations in soil, prevent leaching loss of these cations, and make them available for uptake by plants.

37 Origin of Cation Exchange Capacity (CEC) in Clay Minerals Mainly found in 2:1 clays Ca 2+ K + Exchangeable cations tetrahedral sheet octahedral sheet tetrahedral sheet Two kinds of CEC: Ca2+ K+ Permanent (through isomorphic substitution) at the time of clay mineral formation ph dependant

38 Permanent CEC 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. It cannot be undone. Examples of isomorphous substitution: Si Al Aluminum (Al ) substitution for Silicon (Si )in tetrahedral sheet. Magnesium (Mg 2+ ) substitution for Aluminum (Al 3+ ) 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.

39 ph Dependant CEC Some variable or ph-dependent charge also occurs at exposed clay edges. If ph rises, H+ dissociates from OH- at clay edges, increasing the CEC. If ph decreases, H+ can be attached to the clay surface OH- groups, causing a decrease in CEC. Under very acidic conditions such as in highly weathered tropical soils, small amounts of positive surface charge can develop (i.e., anion exchange capacity. This variable charge is most important in kaolinite and aluminum and iron oxides, which are abundant in highly weathered soils. The CEC of humus is also ph-dependent.

40 ph and Nutrient Availability

41 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). Base Saturation % = Ca 2+ + Mg 2+ + 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. ) EC Sites (%) CE Soil ph Source: Birkeland 1999

42 Range of Soil ph Relative concentration of H + or OH - Acid Neutral Alkaline ph acid sulfate soils leached soils many fertile soils calcareous soil sodic soil lemon juice pure water soap Source: Jenny The Soil Resource

43 Predict the Effect of Igneous Rock Parent Materials on Soil & Ecosystem Properties. Higher or Lower in Which One? Igneous Rock Parent Material Soil/Ecosystem Property Granite (rich in Gabbro (rich in iron silica) and magnesium) Clay Content Sand Content Available Water Capacity CEC and Bases Ecosystem Biomass S il i tt Soil organic matter, nitrogen,fertility

44 Predict the Effect of Igneous Rock Parent Materials on Soil & Ecosystem Properties. Higher or Lower in Which One? Igneous Rock Parent Material Soil/Ecosystem Property Granite (rich in Gabbro (rich in iron silica) and magnesium) Clay Content Lower Higher Sand Content Higher Lower Available Water Capacity Medium Medium CEC and Bases Lower Higher Ecosystem Biomass Lower Higher Soil organic matter, Lower Higher nitrogen,fertility

45 Effect of Parent Material on Soils and Ecosystems (A Lithosequence) Example from Sierra Nevada Mountains, California (Jenny, 1980) Igneous Rock Parent Material Soil Properties Silicic Rocks Mafic Rocks Organic Carbon % Total Nitrogen % Clay % Exchangeable 5 11 Bases (cmol + /kg)

46 Today s Lab Reactor Woods Identify and describe soil bio- and topo-sequences (logical orders of soils that are different because of position in the landscape) Wear long pants! (poison ivy) Each group will have a soil probe and a soil description kit. You will describe three cores from different landscape positions (summitt, backslope, footslope) We will also walk down the hill to Onion Creek and look at soils along the way. NOTE: Individual paper from today s lab due in two weeks (October 6)

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48 Depth (cm) Bio-sequence - forest member. Hayden - developed under deciduous forest in Des Moines Lobe till Source: Aandahl 1982

49 Approximate Depth (cm) Bio-sequence - Savanna Member Lester - developed in deciduous forest prairie transition ecotone (savanna) Source: Sandor

50 Bio-sequence Prairie Member Clarion soil - Shown to 48 in Source: Sandor

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52 Landscape of toposequence: Clarion - well-drained higher soils (lighter brown tones); Webster dark, poorly-drained wet elongated soils; Okoboji dark, circular, closed depressions; Harps dark circular above Okoboji, more calcareous; Storden very light yellow tops of hills Des Moines Lobe Upland Think about the original vegetation ti recall your visit it to Doolittle Prairie i Source: Lee Burras or Jerry Miller

53 Drainage classes Excessively drained Somewhat excessively drained Well-drained d Moderately well-drained Somewhat poorly drained Poorly drained Very yp poorly drained Permanently wet

54 Compare the Webster to the Nicollet and Clarion.

55 Upland Soils Clarion-Webster-Nicollet Association Note: Parent materials glacial till or local alluvium Upland depressional soil sequence from center out Okoboji 6, Harps 95, Canisteo 507 Webster depressional, non-circular soil Best drained soils Clarion 138 & Storden 62 but Storden is eroded Nicollet somewhat poorly drained

56 Soil Landscape Model for Central Iowa Hayden-Lester Lester-Storden Association Clarion-Webster-Nicollet Association Coland-Spillville-Zook Association

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