Soils: facts and fiction Note series for Environmental Science ENVI 152

Soil Definition (NRCS) n “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.” NRCS - Natural Resource Conservation Service

Downer soils (NJ State Soil) Found in woodland areas with natural vegetation consisting of mixed oaks, hickory, and scattered pines. Occur on over 291,000 acres in NJ (in all 11 counties of southern/central NJ). Downer was established in the 1960’s in Gloucester County.

Soil Loss n Through erosion (major problem) u Washes out potential nutrients that would be available u Lost nutrients will negatively impact plant diversity

Why Soil Loss? n Development (Key factor) n Clearing of fields for agriculture (LDCs) n Strip mining (Global) n Natural weathering (Forming soils) n Edge effect (Related to Development) n Sea Level Rise (Loss of Coastal Shoreline)

Soil types n Soils are weathered rocks that create smaller particles n Classified as Sand, Silt or Clay n Depending 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

Soil Contamination n Since soils are in the LITHOSPHERE (Crust), they will be exposed to more environmental stresses. n Acid rain is a problem in that it displaces cations in the soil and causes changes in soil chemical compositions and pH

Soil Texture = %Sand, Silt & Clay in a soil. n Soil texture is the single most important physical property of the soil. Knowing the soil texture alone will provide information about: 1) Infiltration of water 1) Infiltration of water 2) Porosity 2) Porosity 3) Nutrient holding ability 3) Nutrient holding ability

Textural Triangle

Particle Diameter Size n Soil particle diameters range over 6 orders of magnitude u 2 m boulders u Coarse fragments > 2 mm u Sand < 2 mm to 0.05 mm u Silt < 0.05 mm to mm u Clay < m

Coarse Fragment n > 2 mm n Gravels, cobbles, boulders n Not considered part of fine earth fraction n Boulders left in valley of Big Horn Mts.(Wy) by a glacier.

Sand n 0.05 mm n Visible without microscope n Rounded or angular in shape n Can contain quartz or calcium carbonate & sometimes minerals n Feels Gritty

Sand n Low specific surface area n Sand has less nutrients for plants than smaller particles n Voids between sand particles promote free drainage and entry of air n Holds little water and prone to drought

Silt n mm n Not visible without microscope n Quartz often dominant mineral in silt since other minerals have weathered away.

Silt n Does not feel gritty n Floury feel –smooth like silly putty n Wet silt does not exhibit stickiness / plasticity / malleability

Silt n Smaller particles – retains more water for plants and have slower drainage than sand. n Easily washed away by flowing water – highly erosive. n Holds more plant nutrients than sand.

Source of Silt

Clay n Wet clay is very sticky and is plastic or it can be molded readily. n Easily formed into long ribbons. n Shrink swell – none to considerable depending on the kind of clay.

Clay n Pores spaces are very small and convoluted u Movement of water and air very slow n Water holding capacity u Tremendous capacity to adsorb water- not all available for plants. n Soil strength- shrink/swell affects buildings, roads and walls. n Chemical adsorption is large

Determining Soil Texture - Feel Method n Wet soil in hand n Make ribbon n Length of ribbon indicates clay content n Grit or lack of grit indicates sand or silt n Smoothness indicates silt

USDA Textural Classes n Sandy soils (coarse) u Fine sand u Very fine sand n Loamy soils (medium) n Clayey soils (fine )

Sandy Soils n Coarse texture u Sands u Loamy sands

Changes in soil texture n Over long periods (1000s yrs) pedologic processes alter soil horizon textures. n As soils get older sand weathers to silt and silt weathers to clay….therefore old soils have more clay.

Naming Soil Horizons n Soil horizons (layers in the soil) are named so differences between soils can be identified. n Naming soil horizons takes practice

Organic Horizons u O - horizon - organic material (no mineral materials) 1) forest litter 2) organic soil or peat soils, or muck

Organic Soil Profile This trenching machine is digging through the Oe horizon of an organic soil. Trenches needed to remove water so the peat will dry before harvest.

Mineral Soil Horizons n A horizon - surface horizons that accumulate n B horizon – usually iron and leached minerals locally n C horizon – more rock and “parent material” A B B (t) B (C) C