Soil is, by far, the major resource for food production worldwide

Transcription

1 Soil is, by far, the major resource for food production worldwide

2 Soils Function As: 1 Medium for plant growth 2 Recycling system for nutrients and organic waste 3 Habitat for soil organisms 4 System for water supply and purification 5 Engineering medium

3 Soils are variable and locally heterogeneous

4 Lots of variability even within highly similar categories These profiles all represent Ultisols

5 Soil Comprises: (volume basis) Organic Matter 5% Mineral Matter 45% Solids Soil Water (solution) 30-20% Pores Soil Air 20-30% Soil Solids Soil Pores Weight: Mineral = 95% Organic = 5%

6 1m Soil is an important part of the landscape 1 Pedon: basic soil unit 1m 2 x 1-2 m deep 1m

7 Primary Particles Sand Silt Differentiated solely on the basis of size Clay

8 Shape of primary particles Sand and silt: cubic or spherical Clay: lath or plate shape Mature quartz sand from the St. Peters formation, Missouri a illite 15K x a

9 Nature and properties of different size fractions Sand and silt: No plasticity (ability to deform when molded) No water holding capacity No cohesion Clays give soil many of its most important properties: water holding capacity, nutrient retention, ion exchange capacity, etc. Reactivity Adsorption Plasticity Surface Area } } } } Sand silt clay colloidal clay

10 Soil particle size and resultant surface area (Data from Foth, 1978) Separate Diameter (mm) a Volume b (mm 3 ) Number of particles per gram Surface area in 1 gram (cm 2 ) Very coarse sand Coarse sand Medium sand Fine sand , Very fine sand , Silt ,776, Clay < ,260,853,000 8,000,000 b a United States Department of Agriculture classification system b Surface area of platy montmorillonite determined, all others calculated for spheres of largest size permissible by class

11 American Society for Testing and Materials Colloids Clay Silt Fine sand Coarse sand Gravel American Association of State Highway Officials Soil Classsification Colloids Clay Silt Fine sand Coarse sand Fine gravel Medium gravel Coarse gravel Boulders Unified Soil Classification (Corps of Engineers, Department of the Army, and Fines (silt or clay) Fine sand Medium sand Coarse sand Fine gravel Coarse gravel Cobbles Bureau of Reclamation) Civil Aeronautics Administration Soil Classification Clay Silt Fine sand Coarse sand Gravel U.S. Department of Agriculture Soil Classification Clay Silt Very Fine sand Fine sand Medium coarse Very Coarse sand sand sand Fine gravel Coarse gravel Cobbles Sieve sizes ½" ¾" 3" Particle size - mm

12 %CLAY sandy clay sandy clay loam clay clay loam 40 silty clay 50 silty clay loam % S ILT sand 90 loamy sand 80 sandy loam loam 50 % SAND 40 silt loam silt 90 Arrows indicate orientation of the axis. 0

13 %CLAY sandy clay sandy clay loam clay clay loam 40 silty clay 50 silty clay loam % S ILT sand 90 loamy sand 80 sandy loam loam 50 % SAND 40 silt loam silt 90 Arrows indicate orientation of the axis. 0

14 Horizons are layers in the soil developed during soil genesis

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16 Horizons combine to produce the SOIL PROFILE A Horizons Organic Matter accumulation E Horizons Zone of losses Eluvial B Horizons Zone of accumulation Illuvial C Horizons Parent Material

17 How do we tell different horizons (and soils) apart? Color Texture Aggregation Consistency Porosity Organic matter content Soil water ph Nutrient status

18 Soil Profiles Vary Greatly Kansas Mollisol Virginia Ultisol Australia Vertisol

19 Ap C Sandy, mixed, mesic Oxyaquic Ustifluvents

20 Fillmore silt loam -argialboll A E (mollic epipedon) Bt C stax60.jpg

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22 Tongueing of the albic horizon

23 This soil has an A horizon 16 inches thick over a thin Bt horizon. The arrows mark the top and bottom of the Bt where clay has accumulated. Below the Bt is the C horizon. The lowest arrow points to a spot of carbonate. The glacial till from which this soil formed was rich in calcium carbonate. Over time, the carbonate has been removed from the upper part of the profile by water leaching through the soil. In a humid climate such as Minnesota, where carbonate is found in the subsoil, weathering has not progressed sufficiently for the horizon to be called a B horizon. This is designated the C horizon.

24 Soil Age Weathering occurs from the top down Soils are pedologically older at the surface and younger at depth Soil formation begins at the boundary of the B & C horizons Chronologically, soils may be the same age from top to bottom, or younger at the surface than at depth

25 Weathering factors operate most intensely here Oldest material pedologically, although new material is also added here A Horizons Organic Matter accumulation E Horizons Zone of losses B Horizons Zone of accumulation Soil formation initiated here C Horizons Parent Material

26 Jenny s equation of soil formation S (or s) = f(cl, o, r, p, t) where: S = state of the soil s = state of an individual soil property - cl, o, r, p, t are the state functions

27 Jenny defined a series of factors that determine the State of any soil He cleverly named these STATE FACTORS Parent Material Topography Organisms Climate Time - Lithofunction (p) - Topofunction (r) - Biofunction (o) - Climofunction (cl) - Chronofunction (t)

28 Parent Material: Minerals from which soil forms vary from place to place Different minerals weather at different rates

29 Sources of Parent Material Residual (weathered out of underlying bedrock) Transported Water (flood plains, deltas, lake and marine sediments Wind (loess) Gravity (talus) Glaciers (outwash moraines [till])

30 Major Physiographic and Regolith Regions of the United States

31 Soil Orders of the United States

32 Organisms - notably Vegetation Most striking contrast is grassland vs. forest Grasslands - deep, usually organic-rich surface layers * fine roots inject organic matter into the A horizon Forests - usually shallow - thick litter layer, but thin A * heavy roots have little annual die-off, little organic matter injection, BUT needle fall creates a high organic matter layer on surface

33 Grassland soils A horizon is thick, due to annual production of fine roots, less clay loss than forest - Less iron and aluminum translocation from A to B than in forest A B

34 Forest Soils Typical litter layer, thin A horizon, notable loss of iron and aluminum to the B horizon, often resulting in spodic B horizon A E B

35 Topography - relief 2 major effects : Distribution of solid materials Controls on microclimate Precipitation Precipitation

36 Precipitation Precipitation Erosion Erosion Erosion

37 Precipitation Precipitation Erosion Erosion Erosion Accumulation

38 Topographic Effects on Soil Development

39 Climate Moisture and Temperature Climate exerts control over rates of weathering (reactions proceed about 2X with a 10 C increase in temperature) Climate controls leaching rate (amount of precipitation) Climate controls the vegetation type

40 Distribution of Biomes

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42 Distribution of World Soils

43 In General: Moisture (humidity and precipitation) increase from west to east in the U.S. Temperature increases from north to south Sooo.. Soils of the southeast are * most highly weathered * deepest * dominated by simple clay minerals and Fe & Al oxides * pedologically the oldest

44 Organic matter tends to increase from south to north e.g. tundra is all OM due to cold temperatures slowing OM decomposition by microbes Soils of the north are thinner and less well developed * temperature slows weathering * in areas of glacial deposits, the parent material is only 12,000 years old * minerals tend to be those representing the earlier stages of weathering (i.e. not clays)

45 Climate Effects on Soil Development

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47 Geologic Regions of Virginia

48 Soils of Virginia

49 Alfisols The central concept of Alfisols is that of soils that have an argillic, a kandic, or a natric horizon and a base saturation of 35% or greater. They typically have an ochric epipedon, but may have an umbric epipedon. They may also have a petrocalcic horizon, a fragipan or a duripan.

50 Entisol The central concept of Entisols is that of soils that have little or no evidence of development of pedogenic horizons. Many Entisols have an ochric epipedon and a few have an anthropic epipedon. Many are sandy or very shallow.

51 Inceptisols The central concept of Inceptisols is that of soils of humid and subhumid regions that have altered horizons that have lost bases or iron and aluminum but retain some weatherable minerals. They do not have an illuvial horizon enriched with either silicate clay or with an amorphous mixture of aluminum and organic carbon. The Inceptisols may have many kinds of diagnostic horizons, but argillic, natric kandic, spodic and oxic horizons are excluded.

52 Histosols The central concept of Histosols is that of soils that are dominantly organic. They are mostly soils that are commonly called bogs, moors, or peats and mucks A soil is classified as Histosols if it does not have permafrost and is dominated by organic soil materials.

53 Ultisols The central concept of Ultisols is that of soils that have a horizon that contains an appreciable amount of translocated silicate clay (an argillic or kandic horizon) and few bases (base saturation less than 35 percent). Base saturation in most Ultisols decreases with depth.

54 Virginia s State Soil: Pamunkey

55 The State Soil of Virginia: Pamunkey Description: Fine-loamy, mixed, semiactive, thermic Ultic Hapludalfs Surface layer: dark brown fine sandy loam Subsoil - upper: yellowish red clay loam Subsoil - lower: yellowish red sandy loam Substratum: yellowish brown and reddish brown, stratified sand and gravel Pamunkey soils formed in stream terrace sediments in the James River drainage basin of Virginia. These sediments were from every physiographic province in the Virginia Commonwealth. The farm where the Pamunkey soils were first identified is near Jamestown, Virginia. It is considered to be the oldest tilled farm in the United States. The Jamestown historic farm is now in a conservancy program for agricultural use by James City County. It is very likely that the first settlers at Jamestown were able to survive because of the food they produced on these fertile soils. The Pamunkey Tribe and other Indian Tribes were the first people to recognize the natural ability of this soil to produce food. In recent years these soils have produced record yields of corn and wheat.

56 Aaron Mills Department of Environmental Sciences UVa

57 Mineral Weathering - Rock to Regolith Weathering = the chemical and physical breakdown of rock materials during exposure to air, moisture, and organic matter. 2 types of weathering 1.chemical decomposition changes the chemical makeup (mineralogy) of the solids 2. mechanical - disintegration creates smaller pieces from larger ones

58 Chemical Weathering 1. Carbonic acid formation: H 2 O + CO 2 H 2 CO 3 + H + + (HCO 3 ) - (water + carbon dioxide carbonic acid + hydrogen ion + bicarbonate ion) * 2. Feldspar hydrolysis: 4KAlSi 3 O 8 + 4H + + H 2 O 4K + + AlSi 4 O 10 (OH) 8 + 8SiO 2 (potassium feldspar + hydrogen ion + water potassium ion + kaolinite + silica)

59 Other Important Rxns 3. oxidation of ferromagnesium minerals 4FeO + 2H 2 O + O 2 (iron oxide + water + oxygen 4. dissolution of carbonates 4FeO OH geothite) CaCO 3 + H 2 CO 3 Ca (HCO 3 ) - (calcium carbonate + carbonic acid calcium ion + bicarbonate ions)

60 Susceptibility to Weathering Carbonates: Gypsum > Limestone > Silicates: Ca feldspar > Na feldspar >K feldspar > Quartz

61 Mechanical Weathering Mechanisms 1. Temperature changes a. freeze-thaw b. heating and cooling 2. Biological Decomposition Disintegration 3. Exfoliation fractures