Soils

1
Chapter 14

• Soils

2
What is Soil?

• Relatively thin surface layer of the Earths
  curst consisting of minerals and organic matter
  that has been modified by natural agents such as
  weather
• Formed from rock (parent material) that is slowly
  broken down or fragmented into smaller particles
  by biological, chemical or physical weathering
  processes.
• Takes 200-1000 years to make 1-inch of topsoil.

3
Three Types of Weathering

• Biological weathering plant roots, acids from
  lichens
• Chemical weathering acid rain
• Physical weathering freeze/thaw cycle and
  topography/slope

4
What is Soil Made of?

• 45 mineral particles
• 25 water
• 5 organics
• 25 air

5
Soil Composition (cont.)

• Mineral portion of soil
• provides anchorage for roots
• Provides essential nutrients
• Provides pore spaces
• Rock rich in aluminum create acidic soils.
• Older rocks gt more weathered less nutrients

6
Soil Composition (cont.)

• Litter, dead animals/plant, dung
• Create organic part of soil
• Increases water holding capacity of soil
• Humus black or dark brown organic material that
  remains after decomposition.
• Last for 20 years in soil.

7
What is pore space?

• Pore spaces in soil take up 50 of soil volume
  and are filled with water (soil water) or air
  (soil air)
• Water found in small pores (lt0.05 mm diameter)
• Air found in big pores.

8
Definitions

• Leaching when percolating (seeping) water
  removes dissolved materials from soil. They get
  carried downward.
• Illuviation deposition of dissolved material by
  water as it percolates down.
• Soil horizons distinctive horizontal layers of
  soil.
• Soil profile vertical section from surface to
  parent material showing soil horizons.

9
Soil Horizons

• O horizon organic material
• A horizon top soil high in organics, may be
  nutrient poor, dark colored
• E horizon heavily leached zone between the A
  B horizons
• B horizon subsoil light colored, often zone of
  illuviation, typically rich in iron and aluminum
  clay.
• C horizon weathered bedrock
• Bedrock parent material

10
Soil Profiles
11
Soil Organisms

• Microscopic bacteria, fungi, algae, and
  protozoa
• Macroscopic plant roots, insects, earthworms,
  moles, snakes
• Worms are very important
• Breakdown debris
• Put nutrients back into soil via their castings
• Aerate the soil

12
Nutrient Cycling

• Movement of nutrient materials from soil to
  organisms and back again

13
What are the Physical Characteristics of Soil

• There are 2 key physical characteristics of soil
  Texture and Acidity
• Soil texture structural characteristics
• gt determined by (by weight) of sand, silt and
  clay
• Sand 0.05 2 mm in diameter
• Silt 0.002 0.05 mm in diameter
• Clay - lt 0.002 mm in diameter
• clay has the greatest surface area

14
Soil Texture (cont.)

• Soil minerals are found typically in the form of
  ions gt charged particles
• Anions negatively charged particles
• Cations positively charged particles

15
Soil Texture (cont.)

• Loam ideal for agriculture
• 40 sand drain soil, add in air
• 40 silt holds organics
• 20 clay hold nutrients/minerals
• Know Table 14-2

16
Soil Acidity

• Measured on a pH scale
• Most fall between pH 4 8
• Solubility of mineral nutrients vary pH
• Acidic soils have decreased ability to bind
  positively charged part as most sites are taken
  up by H
• Optimal pH for plants 6 to 7

17
Major Soil Groups

• Spodosols found in colder climes with ample
  precipitation and good drainage
• Coniferous forest
• Acidic litter gt distinct ash-grey E-horizon and
  dark brown B-horizon
• Alfisols Temperate deciduous forests
• Brown to gray-brown A-horizon
• A-horizon is low on minerals due to sufficient
  precipitation
• Sufficient fertilization from leaf litter good
  O-horizons

18
Major Soil Groups (cont.)

• Mollisols temperate, semi-arid grasslands
• Very fertile
• Thick dark A-horizon that is rich in humus
• Aridsols arid regions
• No leaching (no precipitation)
• Low organics higher mineral content
• Thin A-horizon

19
Major Soils Groups (cont.)

• Oxisol tropical subtropical area
• Low nutrients
• Thick, highly leached B-horizon

20
Soil problems

• Soil Erosion wearing away or removal of soil
  from land, often by wind and rain.
• Mineral Depletion agricultural system that uses
  soil nutrient but disrupts nutrient cycling so
  its not returned to the land (examples farming
  techniques, slash burn)
• Salinization from irrigation
• Desertification degradation of grassland
  other productive lands into desert

21
Soil Conservation

• Conservation tillage residues from previous
  crops left in soil
• No-tillage leaves soil undisturbed over winter
  with previous crops in place.
• Crop rotation plant series of different crops
  in same field over a period of years
• Typically alternating with legumes that increase
  soil fertility thru relationships with bacteria
  that fix atmospheric nitrogen

22
Soil Conversation (cont.)

• Contour plowing plow/plant to natural curves of
  land
• Strip cropping alternative strips of different
  crops with contouring
• Terracing produce level areas to grow drops and
  minimize soil erosion.

23
Fertilizers

• Two types Organic and Inorganic
• Organic
• Manure
• Bone meal
• Compost (tilled into soil)
• Mulch (placed on top)
• Inorganic
• Nitrogen/phosphorus

24
Fertilizers (cont)
25
Soil Reclamation

• Stabilize land to prevent further erosion
• Restore land to former fertility
• Shelter belts rows of trees that lessen winds
  and therefore soil erosion

26
Soil Conservation Policies

• Soil Conservation Act of 1935
• Formed Soil Conservation Service (now Natural
  Resource Conservation Service)
• Mission is to work with U.S. citizens on
  conserving natural resources
• Food Securtiy Act of 1985 (Farm Bill)
• Created 2 programs
• Conservation Compliance Program
• Conservation Reserve Program

27
Food Security Act of 1985 (cont.)

• Requires farmers to develop and adopt a 5-year
  conservation plan
• Created Conservation Reserve Program (CRP)
  voluntary program to pay farmers to stop
  producing crops on high erodible farmlands.

28
More policies

• Federal Agricultural Improvement Reform Act
  (Farm Bill) of 1996
• Restructured earlier farm bill to have fewer
  inspections and more lenient inspectors
• Grassland Reserve Program included in 2002 Farm
  Bill
• Pays farmers to protect virgin and improved
  pastureland for a period of at least 10 years.