Soil

1. Soil Characteristics, Degradation, and Conservation

2. What is soil? • Soil is derived from rock, and contains a large biotic component • Supports plant life • What makes up soil • 50% mineral matter • Up to 5% organic matter (living & dead microorganisms and decaying material) • Rest is composed of water and air • Soil itself can be defined as an ecosystem • Composed of living and nonliving components

3. How does soil form? • Parent material • Base geological material in a particular location • Examples: • Lava • Volcanic ash • Rock or sediment deposited by glaciers • Wind-blown dunes • Sediments deposited by rivers in lakes, oceans, etc. • Bedrock • Continuous mass of solid rock that makes up Earth’s crust

4. Processes responsible for soil formation… • Weathering: the physical, chemical, and biological processes that break down rocks and minerals • First step of soil formation • Turns large particles into small particles Biological Weathering Physical Weathering Chemical Weathering

5. Physical or mechanical weathering • Breaks down rocks without triggering a chemical change in the parent material • Main forces: wind and rain • Varied by daily and seasonal temperature variation • Causes the thermal expansion and contraction of the parent material • Areas with extreme temperature fluctuations have rapid rates of physical weathering • Water freezing and expanding in cracks – causes physical weathering • Crystalline structure occurs in the water when it freezes

6. Chemical weathering • Occurs when water or other substances chemically interact with the parent material • Warm, moist conditions usually accelerate the rate of chemical weathering • Biological weathering • Occurs when living things break down parent material by physical or chemical processes • Ex. Lichens initiate primary succession by producing acid • This acid chemically weathers the rock • Ex. Tree roots accelerate weathering as their roots grow and rub against rock • Also accelerate chemical weathering through leaf decomposition and chemical release from the roots into the soil

7. Role of erosion in soil formation… • Erosion: the dislodging and movement of soil from one area to another • Deposits material it has depleted from another • Occurs when soil has no or little vegetation • Surface is exposed to water and wind degradation • Although it can sometimes help build new soil in the long term, on a human timescale erosion is perceived as destructive

8. Role of biological activity in soil formation… • Deposition, decomposition, and accumulation of organic matter • Deposition • As living organisms die or deposit waste, the material is incorporated into the soil and mixes with minerals • Ex: Trees drop their leaves → leaves decompose → detritivores and decomposers break down organic material → nutrients from leaves are added to the soil • Decomposition • Complex organic molecules are broken down into smaller ones • Partial decomposition of organic matter creates humus •   dark, spongy, crumbly mass of material • Soils with humus hold moisture well and are good for plant growth Decomposition Video: http://techalive.mtu.edu/meec/module10/Decomposition2.html

9. Soil Horizons • Horizon: distinct layer of soil • Soil profile: cross section as a whole • From the surface to the bedrock • Six major horizons • O Horizon – “litter layer”, consists of organic material deposited by animals and plants • A Horizon – “topsoil”, consists of some organic material mixed with mineral components • E Horizon – zone where minerals and organic material pass through to mix in the topsoil • B Horizon – “subsoil”, where minerals and organic matter accumulate • C Horizon – consists of weathered parent material unaltered or slightly altered by soil formation • R Horizon – pure parent material • Few soil profiles consist of all six horizons

10. Soil by Biome • Tropical Rainforest • Very poor and infertile • Weathering has washed away most of the nutrients • Little organic matter because the warm temperatures encourage quick decay • Temperate Deciduous Forest • Very fertile • Replenished with falling leaves, twigs, and dead organisms • Cool enough temperatures allow slow decay • Grassland • Nutrient rich • large amount of plant material added daily • Contains large portions of clay, that retains water in the soil for later use by plants • Often converted into farmland

11. Desert • Little or no chemical weathering • Erosion, frost, sedimentation, and temperature fluctuations break down the rocky soil into sand • Clay particles, since the silt and sand particles are easily blown away • Taiga • Acidic soil due to needle-like “leaves” • Top layer is covered with rocks • Makes it hard for nutrients to reach the soil • Plants are unable to grow between the rocks without difficulty • Tundra • Lack of nutrients due to short growth period during the summer • Permafrost: frozen deep layers of soil • Hard for plants to survive the harsh winters

12. Importance of topsoil for agriculture and ecosystems • Consists of mostly inorganic mineral components • Ex: Weathered substrate • Benefit for plants • Most nutrient-rich horizon • Loose texture • Dark coloration • Strong water-holding capabilities • Due to humus • Vital for agriculture • Agriculture can deplete the organic matter in the topsoil, reducing the soil’s fertility and ability to hold water

13. The Leaching Process • Leaching: process where solid particles suspended or dissolved in a liquid are transported to another location • Ex: Nutrients in soil • Similar effect of a coffee filter • When it rains, water enters the soil, dissolves some of its components, and carries them downward into the lower horizons

14. Soil Characteristics • Scientists classify soils by… • Color • Texture • Structure • pH • These characteristics affect soil’s ability to provide plants with nutrients

15. Color • Indicates the composition and fertility • Black and brown: rich in organic matter • Pale gray and white: leaching or low organic content • Farmers used to rely on the color of topsoil to determine the area’s potential to support crops and livestock

16. Texture • Determined by the size of particles • The United States Department of Agriculture (USDA) uses 3 categories of soil • Clay: particles less that 0.002 mm in diameter • Silt: particles 0.002-0.05 mm in diameter • Sand: particles 0.05-2 mm in diameter • Loam: mixture of all three soil particles

17. Soil texture influences a soil’s “workability” • Soil porosity: a measure of the size of spaces between particles • The finer the particles, the smaller the spaces between them • Harder for water and air to move throughout the soil • Slows infiltration and reduces the amount of oxygen available to organisms in the soil • Large soil particles allow water to pass through quickly • Roots unable to take in water • Require frequent irrigation • Silty and loam soils are the best for plant growth

18. Structure • Measure of the “clumpiness” of soil • Encourages soil productivity • Soil clumps that are too large discourage plant roots from growing • Plowpan: a hard layer of soil that resists water transportation and root penetration, due to farmers repeatedly plowing the same field at the same depth • Repeated tilling can compact soil • makes it less able to absorb water

19. pH • pH: the degree of acidity or alkalinity • Influences a soil’s ability to support plants • Plants usually die in soils that have extremely acidic or alkaline pHs • Moderate variation influences the availability of nutrients for plants

20. Cation Exchange • Cation: positively charged ion • Held in soil particle surfaces that are negatively charged • Ex: Calcium, magnesium, potassium • Cation exchange: process through which plants gain nutrients • Plant roots donate hydrogen ions to the soil in exchange for cations 2. Soil particles then replenish with exchange with water in the soil

21. Cation exchange capacity: a soil’s ability to hold cations • Prevents them from leaching • Makes them available to plants • Useful measure of soil fertility • Soils with fine texture and rich in organic matter have the highest • As soil pH decreases (more acidic), cation exchange capacity diminishes • Nutrients leach away – soil then may supply plants with harmful aluminum ions • Why acid rain harms plants

22. Soil and Its Relationship to Agriculture Irrigation is the controlled application of water for agricultural purposes through manmade systems to supply water requirements not satisfied by rainfall.

23. Irrigation Methods • Center pivot-This is a form of overhead irrigation. Steel or aluminum pipes are joined together, supported by trusses, mounted on wheeled towers. The sprinklers are situated on the length of the tower and they move in a circular motion. • Drip-A planned irrigation system in which water is applied directly to the Root Zone of plants by means of applicators (orifices, emitters, porous tubing, perforated pipe, etc.) operated under low pressure with the applicators being placed either on or below the surface of the ground. • Flood-The application of irrigation water where the entire surface of the soil is covered by ponded water.

24. Furrow-A partial surface flooding method of irrigation normally used with clean-tilled crops where water is applied in furrows or rows of sufficient capacity to contain the designed irrigation system. • Gravity-Irrigation in which the water is not pumped but flows and is distributed by gravity. • Rotation-A system by which irrigators receive an allotted quantity of water, not a continuous rate, but at stated intervals. • Sprinkler-A planned irrigation system in which water is applied by means of perforated pipes or nozzles operated under pressure so as to form a spray pattern.

25. Sub-irrigation-Applying irrigation water below the ground surface either by raising the water table within or near the root zone or by using a buried perforated or porous pipe system that discharges directly into the root zone. • Traveling gun-Sprinkler irrigation system consisting of a single large nozzle that rotates and is self-propelled. The name refers to the fact that the base is on wheels and can be moved by the irrigator or affixed to a guide wire. • Supplemental-Irrigation to ensure increased crop production in areas where rainfall normally supplies most of the moisture needed. • Surface-Irrigation where the soil surface is used as a conduit, as in furrow and border irrigation as opposed to sprinkler irrigation or sub-irrigation.

26. Problems Due to Irrigation • Water-logging- the irrigation water eventually raises the water table in the ground -- the upper level of the groundwater -- from beneath. • Salinization-occurs in warm and dry locations where soluble salts precipitate from water and accumulate in the soil. • Leaching-The removal of soluble material from a soil or rock, through the percolation of water.

27. Solutions/Preventions of irrigation problems: • Use soil moisture detectors so that the crops are only watered when it is needed • Use time controlled valves on gravity flow systems • Use water that is low in salinity • Only use the amount of water needed to grow the plant, no extra

28. Soil Degradation • Population and consumption increase • As the population of humans increase, so does the consumption and call for goods. More crops must be grown which can hurt the soil. • Erosion can degrade ecosystems • Erosion can ruin the soil and prevent plants from growing. Without the proper producers in an ecosystem, then there can be no other organisms either.

29. Soil erodes by several mechanisms sheet-Detachment of soil particles by raindrop impact and their removal down slope by water flowing overland as a sheet rill-An erosion process in which numerous small channels, typically a few inches deep, are formed. It occurs mainly on recently cultivated soils or on recent cuts and fills. gully-Water flows in narrow channels during or immediately after heavy rains or melting snow. • Conventional tillage-Full width tillage which disturbs all of the soil surface and is performed prior to and/or during planting. • Tillage is the agricultural preparation of the soil by ploughing, ripping, or turning it.

30. Soil erosion is a global problem • Erosion is a process that removes soil layers and carries them away from farmer's fields to bodies of water or other land. Erosion results in the loss of valuable soil and its nutrients that are necessary for crops to grow. There are three primary kinds of erosion: wind, water, and tillage. In areas where the land is especially flat or dry, wind erosion is a problem. • Soil erosion results in the loss of soil fertility and makes the land barren. There are more than 25 million hectares of barren lands in the world now.

31. Desertification reduces productivity of arid lands • Deterioration in soil and plant cover have adversely affected nearly 50 percent of the land areas as the result of human mismanagement of cultivated and range lands. • Overgrazing and woodcutting are responsible for most of the desertification of rangelands, cultivation practices inducing accelerated water and wind erosion are most responsible in the rain-fed croplands, and improper water management leading to salinization is the cause of the deterioration of irrigated lands.

32. The Dust Bowl • Between 1879 and 1929 the cultivation of land in the states of Oklahoma, Texas, Kansas, New Mexico, and Colorado soared. • Farmers grew abundant wheat and ranchers grazed thousands of cattle • Both types of agriculture contributed to erosion by removing native grasses and breaking down soil structure.

33. In the early 1930s, a drought occurred in the region. • Strong winds began to erode millions of tons of top soil. • The winds carried the dust over a thousand miles, blackening rain and snow in New York and Vermont. • The most affected region in the southern Great Plains became known as the Dust Bowl. • The “black blizzards” of the Dust Bowl forced thousands of farmers off their land

34. Works Cited • http://ga.water.usgs.gov/edu/irquicklook.html • Old textbook & new textbook

35. The Soil Conservation Service Objective: To slow soil degradation.

36. The Soil Conservation Service • In response to the devastation in the Dust Bowl the U.S. Congress passed the Soil Conservation Act of 1935, which established the Soil Conservation Service (SCS).

37. The Soil Conservation Service • The SCS worked directly with farmers to develop conservation plans for individual farms which followed several aims and principles: • Assessing the land’s resources, problems, and opportunities. • Prepare an integrated plan for each property. • Ensure that conservation plans correspond with users’ objectives. • Implement conservation measures on individual properties to contribute to the overall quality of life.

38. The Soil Conservation Service • SCS promoted soil-conservation practices through county-based conservation districts. These districts: • Operate with federal direction, authorization, and funding. • Implement local soil conservation programs, in hopes of getting residents to plan ahead.

39. The Soil Conservation Service • In 1994 the SCS expanded to include water quality protection and pollution control. • It was renamed the Natural Resources Conservation Service. • The SCS inspired similar efforts around the world.

40. How farmers can protect against soil degradation:

41. Crop Rotation • The practice of growing various crops on the same piece of land in a planned sequence. • An example of a common sequence would be a rotation between high and low residue crops • i.e. wheat and soybeans.

42. Contour Farming • The use of plowing to form ridges which change the direction of run-off so that it can settle into the soil and prevent soil erosion.

43. Terracing • The creation of “steps” on a hillside so water can be contained. • The end result looks like a staircase. Rice terracing

44. Intercropping • The cultivation of two or more crops in the same area. • Increases plant biodiversity to help disguise plants from insect species. • Increases the density to suppress weed growth. • Improves the overall health of crops and decreases chance of disease.

45. Strip Cropping • The practice of growing planned rotations of row crops, forages, small grains, or fallow in a systematic arrangement of equal width strips across a field.

46. Alley cropping • A type of intercropping that involves arranging crops in alternate rows.

47. Agroforestry • An approach of combining trees and shrubs with crops and/or livestock to produce a more diverse, productive, profitable, healthy and sustainable land-use.

48. Shelterbelt • A plantation usually made up of trees and shrubs to protect against wind and prevent soil erosion.

49. Tillage • The agricultural preparation of soil by ploughing, ripping, or turning it. • Different levels of tillage: • Intensive: leaves 15% or less of crop residue in the soil • Reduced: leaves 15%-30% of crop residue in the soil. • Conservation: Leaves a minimum of 30% of crop residue in the soil.

50. Many different acts were passed to promote, protect, and restore soil conservation. • These acts were passed in the late 20th century. • They were both in the US and some were international.