3.4 The Soil System

Its more than just dirt -Mr. Shefferly3.4 The Soil System1The Soil SystemSoil is a complex mixture ofEroded rockMineral nutrientsDecaying organic matterWaterAirBillions of living organisms (DECOMPOSERS!!)

2Soil Formation Over Time

3Three Processes of Soil FormationVery Slow Process1. Weathering of rock (mechanical)2. Deposition of sediments by erosion (mechanical)3. Decomposition of organic matter (chemical)

4Soil System Food Web

5Soil horizons (layers)Soil LayersO - (Organic) Freshly fallen leaves, twigs, animal waste, fungiA- Mixture of partially decomposed organic matterB- (Subsoil) Nutrients leached from A Plant RootsC- (Parent Material) largely inorganic material

6Important Cycles (Nitrogen Cycle)

7Nitrogen Cycle TermsNitrogen Fixation: Atmospheric nitrogen (N2) is made available to plantsNitrification: Bacteria in soil convert ammonium (NH3) to nitrite(NO2) and then nitrates (NO3).Denitrification: Bacteria in soil nitrates (NO3) to nitrogen gas (N2)Assimilation: Living organisms take in the nitrogen to make proteinsAmmonification: Bacteria and fungi decompose waste and organisms and allow for ammonia to be released into the soil

8Processes in the Nitrogen Cycle

9Soil Particles Clay (very fine particles >0.002mm) Silt (fine particles 0.05mm-0.002)Sand (medium-sized particles 2mm-0.05mm)Gravel (large coarse particles < 2mm) Soil Texture is determined by the relative amounts of the different types and sizes of mineral particles

SmallestLargest10Soil Texture Triangle

11Soil Texture Practice Problems1. Sand = 25 % Silt = 15 % Clay = 60 %

2. Sand = 30 % Silt = 35 % Clay = 35 %

3. Sand = ? Silt = 10 % Clay = 40 %

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Soil Permeability Rate at which air and water flow from upper layers of soil to lower layers of soil13Soil TextureNutrient CapacityInfiltrationWater Holding CapacityAeration Workability Clay GoodPoorGoodPoorPoorSiltMediumMediumMediumMediumMediumSandPoorGoodPoorGoodGood14Soil ErosionMovement of soil, especially surface litter and topsoilTwo main agents of erosionWindFlowing waterOccurs due to loss of plants in soil from:OvergrazingDeforestationIrrigation

Dust Bowl, USA 1930s

15Global Soil Erosion

Stable or nonvegetativeSome concernSerious concern16Top Soil Erosion and Run Off from Farm

17Gully Erosion In Bolivia

18Wind removes topsoil

19Erosion ContinuedErosion is harmful1. Leads to loss of soil fertility and ability to hold water2. Increases runoff of sediment that pollutes water and kills fish.

20DesertificationEnlargement of deserts through human activities Causes: Overgrazing, deforestation, irrigation, and erosion Consequences: Worsening drought, famine, economic losses

21Other Soil IssuesSalinizationWaterloggingIrrigation water contains small amounts of dissolved saltsEvaporation and transpiration leave salts behindSalt builds up in soilPrecipitation and irrigation water move downwardWater table rises22Soil IssuesSalinizationWaterlogging

23ToxificationAn increase in soil acidity ( low pH = more acidic)Caused by leaching of metalsBurning of plant material increases soil pHCan be counteracted by using lime stone to raise the pH and reduce acidityLarge problem in the Ohio valley in the USA due to coal power plants

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Acidity of precipitation measured by the National Atmospheric Deposition Program in 2006. Notice that precipitation is most acidic downwind of the large concentration of power plants in the Ohio Valley.Effect on SoilsNeutralization:The effect of acid rain on the environment depends greatly on the ability of soils to neutralize the acid. Limestone and other rocks and soils containing calcium carbonate are most effective. Acids react with calcium carbonate to produce neutral compounds and carbon dioxide. For example, sulfuric acid and hydrochloric acid react with calcium carbonate:CaCO3 + H2SO4 > CaSO4 + H2CO3H2CO3 > CO2 gas + H2O2HCl + CaCO3 -> CO2 + CaCl2 + H2OThe extent to which soils can neutralize acid rain depends on several factors: type of soil, thickness, weather, and water flow patterns. If the ground is frozen, as in the winter, soil process cannot work, the acid is not neutralized. If the soil is mainly quartz, such as sand, it is resistant to weathering and no bases are present to neutralize acid. If the soil has very little base such as limestone, the acid is neutralized only slightly or with the passage of time, not at all.In the slightly acidic soils in typical evergreen forests in the Northeastern U.S., Canada, and Europe, two other effects can neutralize the acid rain. The acid can be immobilized as the soil or vegetation retains the sulfate and nitrate ions (from sulfuric and nitric acids). Very deep soils have a large capacity to retain sulfate and nitrate ions. From Virtual ChemBook, Elmhurst College: Acid Rain Soil Interactions.Mature forest soils are also able to neutralize the acids in rain. Such soils are acidic and rich in humic acids. Krug (1983) reports that mature soils in New England or Norwegian forests have a pH of 3.8, and they may contain as much acid as would fall in 1000 years of rain at 1m/year with a pH of 4.3. These soils are highly resistant to acid rain. In contrast, thin alpine soils lacking carbonates and humic acid and overlying granite rocks are not able to neutralize acid rain. The same is true for disturbed forests where forest fires and logging have reduced the organic material in the soil, which also make the soil more susceptible to damage by acid rain.Leaching of NutrientsAcids leach nutrients from the soil. They are carried deeper into the ground or into streams, depriving plants of essential elements calcium, potassium, magnesium and trace metals. Normally, metals are attached to clay particles produced by weathering of rocks. The H+ anion of the acid replaces the metal ions in the clay in a process called ion exchange. The metals occur in groundwater as sulphates and nitrates. Two H+ anions displace one Ca2+ or Mg2+ anion or two K+ anions.Release of AluminumAluminum in soils and rock is very insoulable if the pH is greater than 5. More acidic solutiona dissolve aluminum from the soil, and the aluminum is carried into streams and lakes by runoff and groundwater. Effect on Vegetation

Bavaria, Germany, high-altitude forest damaged by acid rain. Photo by Spitzbergler. From AccuWeather. More photos of Bavarian forest by Spitzbergler.In some regions, especially regions where granite is close to the surface and where soils have been degraded by logging and forest fires, the soil has little ability to neutralize the acid. In these regions, acid deposition depletes the available plant-nutrient cations Ca2+, Mg2+, and K+, it increases the leaching of aluminum, and it increases the amount of sulfur and nitrogen in the soil. All lead to weakening of trees, leading to their death by bark beetle infestations and disease.Some of the most dramatic effects on forests have been observed in Europe. In 1983, a survey in West Germany showed that 34% of the country's total forest is damaged by air pollution. This included about one half of the famous Black Forest. Switzerland has recorded damage to 14 % of her forest trees...

Vogelmann, measured the reproductive capacity of the forest by counting the total trees in an area. Red spruce dropped from 6,000 trees to 1,000 trees, a decline of 80 % from 1965 to 1983. Very few pine cones and young trees were found. Sugar maple tree counts dropped 84 % and beech tree counts dropped 63% over the same time period...

Acid rain or acid cloud droplets that fall on the leaves and needles of trees leaches the nutrients from them. Calcium, magnesium, and potassium ions may be removed from the leaves faster than the roots can resupply them. Acid rain in combination with ozone may damage the waxy coating on leaves and needles. This may weaken, damage them, and provide opportunities for diseases to enter the tree.From Virtual ChemBook Elmhurst College Charles E. Ophardt Acid Rain Effects on Forests.Effect on Aquatic Animals When nutrients and metals, including heavy metals and aluminum, are leached from the soil, they are carried by runoff and groundwater into streams and lakes where they kill aquatic life. Aluminum dissolved by acid rain is highly toxic to many aquatic animals, especially young animals including eggs and larvae.Not all species of animals are equally sensitive to acids and aluminum. Some fish species (such as (brown bullhead, yellow perch, golden shiner, brook trout, and white sucker) are tolerant of water with pH < 6, while others (such as Atlantic salmon, tiger trout, redbreast sunfish, bluegill, tiger musky, walleye, and alewife) cannot tolerate such waters. Most fish are killed if pH falls below 5.2 (Driskoll, 2001).In areas where soils have little capacity to buffer acids in water, acidic precipitation can be a problem because the infiltrating acidic water can increase the solubility of metals, which results in the flushing of high concentrations of dissolved metals into surface water. Increased concentrations of naturally occurring metals such as aluminum may be toxic to aquatic organisms. Studies of watersheds have indicated that the length of subsurface flow paths has an effect on the degree to which acidic water is buffered by flow through the subsurface. For example, studies of watersheds in England have indicated that acidity was higher in streams during storms when more of the sub-surface flow moved through the soil rather than through the deeper flow paths. Moreover, in a study of the effects of acid precipitation on lakes in the Adirondack Mountains of New York, the length of time that water was in contact with deep subsurface materials was the most important factor affecting acidity because contact time determined the amount of buffering that could take place. US Geological Survey. Circular 1139, Ground Water and Surface Water A Single Resource. Effects of Atmospheric Deposition on the Quality of Ground Water and Surface Water.Further ReadingA good review article article on acid rain in North America by Driscoll (2001) in BioScience. This is a 700kByte PDF file. For information on acid rain deposition check the acid rain web pages at the EPA. More information is at the National Atmospheric Deposition Program web pages. To understand how emissions trading works and how it has led to a reduction of acid rain in the US, read Clearing The Air: The Truth About Capping and Trading Emissions (a 0.6 MByte PDF file). The USGS has a site on acid rain with examples from Washington DC, especially the effects of acid precipitation on buildings. There is an active monitoring program in the US called the National Acid Precipitation Assessment Program (NAPAP) and they have a brief summary on their web site. Environment Canada has also a very informative web page on acid rain (as well as other environmental issues including ozone hole over the Arctic Ocean). The EPA publishes Emission Reports listing the amounts of pollutants emitted by individual power plants. A European perspective with many good links can be found at the Swedish NGO Secretariat on Acid Rain. ReferencesDRISCOLL, C. T., G. B. LAWRENCE, et al. (2001). Acidic Deposition in the Northeastern United States: Sources and Inputs, Ecosystem Effects, and Management Strategies. BioScience 51(3): 180--198.Krug, E. C. and C. R. Frink (1983). Acid Rain on Acid Soil: A New Perspective. Science 221 (4610): 520-525.Acid rain is widely believed to be responsible for acidifying soil and water in areas of North America and northern Europe. However, factors commonly considered to make landscapes susceptible to acidification by acid rain are the same factors long known to strongly acidify soils through the natural processes of soil formation. Recovery from extreme and widespread careless land use has also occurred in regions undergoing acidification. There is evidence that acidification by acid rain is superimposed on long-term acidification induced by changes in land use and consequent vegetative succession. Thus, the interactions of acid rain, acid soil, and vegetation need to be carefully examined on a watershed basis in assessing benefits expected from proposed reductions in emissions of oxides of sulfur and nitrogen.

Revised on: 5 January, 2009

25Soil ConservationReduce Erosion byWind Reduction: Plant trees or bushes as windbreaks near edges of open fields Improving irrigation: Prevent evaporation of waterSoil Conditioners : Add lime to raise the pH and prevent the soil from become too acidicSoil Fertility: Rotate crops to prevent the depletion of nitrogen in the soil and add natural manure as fertilizer26Soil ConservationImprove farming Methods:TerracingContour plantingStrip cropping with cover cropAlley cropping, agroforestryWindbreaks or shelterbeltsConservation-tillage farming No-tillMinimum tillage

TerracingReduces soil erosion by controlling water runoff by holding water at each level

Contour Planting/ Strip CroppingEach row acts as a small dam to help slow water runoff and reduce soil erosion

Alley CroppingCrops are planted in alleys between trees/shrubsProvides shade and helps to slow down the release of soil moisture

Windbreak in field

Barrier of trees planted around the edge of the cropPrevents wind erosion, provides habitat for birds, and a supply of fuel woodA soil Lab Must!!Simpsons Diversity Index ReviewUse the Simpsons diversity index belowD = ____________N (N-1)___________________ n1(n11) + n2(n2 1) + n3(n3 1) +nk(nk 1)

D = DiversityN = Total number of organisms of all speciesn = number of individuals of a particular species

The higher the D value the more diverse the sample is!!!!!

Now You Try Abundance of OrganismEcosystem AEcosystem Bspecies 135species 274species 32612species 497species 575Diversity3.27Vermicomposting Vermicomposting is the process of having redworms and other decomposer organisms process our organic waste and turn it into a great natural fertilizer (called worm castings).Worm cast = worm poopCreates Healthy Topsoil from waste that would end up in a landfill.