Presentation on theme: "Soils: facts and fiction"— Presentation transcript:
1Soils: facts and fiction Note series for Environmental ScienceENVI 152
2Soil Definition (NRCS) Soil is a natural body comprised of solids (minerals and organic matter), liquid, and gases that occurs on the land surface, occupies space, and is characterized by one or both of the following: horizons, or layers, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment.
3Downer soils are used mostly as woodland. The natural vegetation consists of mixed oaks, hickory, and scattered pines.Downer soils occur on 291,319 acres in New Jersey. These soils are dominantly in the 11 counties of southern New Jersey.Downer soils are on uplands and formed in sandy, Northern Atlantic Coastal Plain deposits.The Downer series was established in the 1960’s in Gloucester County.
4Soil Loss The loss of soils through erosion is a major problem The loss of soil washes out potential nutrients that would be availableThe loss of soil nutrients will negatively impact plant diversityThe loss of soil is becoming a greater problem today than in the past
5Why Soil Loss? Development Clearing of fields for agriculture Strip miningNatural weatheringEdge effectSea Level Rise
6Soil types Soils are weathered rocks that create smaller particles Classified as Sand, Silt or ClayDepending on the location, there are greater compositions of soil types (i.e. New Jersey coastal area has mostly sand, there clay soils in N. New Jersey
7Soil ContaminationSince soils are in the LITHOSPHERE (Crust), they will be exposed to more environmental stresses which will inevitably permeate down the soils possibly toward groundwater.Acid rain is a problem in that it displaces cations in the soil and causes changes in soil chemical compositions and pH
8Soil Texture = %Sand, Silt & Clay in a soil. Soil texture is the single most important physical property of the soil. Knowing the soil texture alone will provide information about:1) water flow potential,2) water holding capacity,3) fertility potential,4) suitability for many urban uses like bearing capacity
9Particle Diameter Size Soil particle diameters range over 6 orders of magnitude2 m bouldersCoarse fragments > 2 mmSand < 2 mm to 0.05 mmSilt < 0.05 mm to mmClay < m
10Coarse Fragment > 2 mm Gravels, cobbles, boulders Not considered part of fine earth fraction (soil texture refers only to the fine earth fraction or sand, silt & clay)Boulders left in valley of Big Horn Mts.(Wy) by a glacier.
11Sand < 2 mm to > 0.05 mm Visible without microscope Rounded or angular in shapeSand grains usually quartz if sand looks white or many minerals if sand looks brown,Some sands in soil will be brown, yellow, or red because of Fe and/or Al oxide coatings.
12SandFeels grittyConsidered non-cohesive – does not stick together in a mass unless it is very wet.
13Sand Low specific surface area Sand has less nutrients for plants than smaller particlesVoids between sand particles promote free drainage and entry of airHolds little water and prone to drought
14Silt < 0.05 mm to > 0.002 mm Not visible without microscope Quartz often dominant mineral in silt since other minerals have weathered away.
15Silt Does not feel gritty Floury feel –smooth like silly putty Wet silt does not exhibit stickiness / plasticity / malleability
16Silt Smaller size allows rapid weathering of non quartz minerals Smaller particles – retains more water for plants and have slower drainage than sand.Easily washed away by flowing water – highly erosive.Holds more plant nutrients than sand.
18Wet clay is very sticky and is plastic or it can be molded readily into a shape or rod. Easily formed into long ribbonsShrink swell – none to considerable depending on the kind of clay.Clay
19Clay Pores spaces are very small and convoluted Water holding capacity Movement of water and air very slowWater holding capacityTremendous capacity to adsorb water- not all available for plants.Soil strength- shrink/swell affects buildings, roads and walls.Chemical adsorption is large
20USDA Textural Classes Sandy soils (coarse) Loamy soils (medium) Fine sandVery fine sandLoamy soils (medium)Clayey soils (fine)
23Changes in soil texture Over long periods (1000s yrs) pedologic processes alter soil horizon textures.As soils get older sand weathers to silt and silt weathers to clay….therefore old soils have more clay.
24Determining Soil Texture - Feel Method Wet soil in handMake ribbonLength of ribbon indicates clay contentGrit or lack of grit indicates sand or siltSmoothness indicates silt
25Naming Soil HorizonsSoil horizons (layers in the soil) are named so differences between soils can be identified.Naming soil horizons takes practice
26Organic HorizonsO - horizon - organic material (no mineral materials) ) forest litter ) organic soil or peat soils, or muck
27Organic Soil Profile This trenching machine is digging through the Oe horizon of anorganic soil.Trenches needed toremove water so thepeat will dry beforeharvest.
28Mineral Soil Horizons A horizon - surface horizons that accumulate A B B (t)B (C)C