nancy van wagoner, acadia university soils nancy a. van wagoner acadia university

Nancy Van Wagoner, Acadia University

Soils

Nancy A. Van Wagoner

Acadia University


What is soil?

Mineral Matter Organic Material

– litter (undecomposed)– humus (decomposed)

light, spongy absorbs water

– water– air


Soil Formation

Weathering– converts bedrock to regolith

regolith = layer of rock and mineral fragments produced by weathering

interaction of weathered mineral matter with organic matter produces soil


Composition of soil in good condition for plant

growth overhead


Soil Profile (fig. 10.15)


O Layer

organic layer mostly litter and humus little mineral matter


A Horizon Zone of Leaching

– receives rain first, so soluble minerals are leached out contains most organic material (humus) zone of intense biological activity

– roots– burrowing animals– worms– micro-organisms

mostly clays


B Horizon

Zone of accumulation (subsoil)– precipitation of ions dissolved from Horizon A– little organic material


C Horizon

partially altered bedrock very little organic matter merges at the base with bedrock


Soil Forming Factors

Parent material or bedrock type Time Development of organic material Slope angle and aspect Climate


Parent Material or Bedrock Type

Influences– rate or weathering or soil formation

mineralogy (mineral stability) of bedrock consolidation of bedrock

– chemical composition of soil parent material provides nutrients to the soil

– texture of the soil granite produces sandy soil basalt produces clayey soil


Time It takes a long time to form soil Generally, the longer the soils has been forming the

thicker and more distinctly layered it is Soil is always being eroded from the surface by

– natural processes– anthropogenic processes (plowing and tilling)

At the same time weathering deepens the soil If the rate of erosion exceeds the rate of soil generation

the soil is lost and it can take thousands of years to form again.


Development of Organic Material

Organic material in soil promotes chemical weathering and aids in moisture retention– temperate latitudes - thick layers of humus– tropics - decay so rapid that little humus

accumulates– Arctic - little organic matter


Slope Angle

On steep slopes soil is poorly developed because it gets eroded

optimum slope = flat to undulating


Climate controls: whether chemical or mechanic

weathering dominate amount of water available for

weathering and leaching rates of reactions (temperature

dependant) abundance and type of plants and

bacteria which are available as soil forming agents


Soil Types Fig (10.17)

based primarily on climate classified according to the minerals

present in layers A and B 3 main types

– Pedalfers– Pedocals– Laterites


Pedalfer

form Sin areas of high rainfall rain leaches mineral from A and B

horizons Some Fe and Al oxides in horizon B

– but, not soluble material, ie. carbonate


Pedocals

form in dry, warm climate (western US) soil water evaporates leaving behind

precipitates of CaCO3 layer B contains pellets and nodules of

CaCO3 called caliche


Laterite form in extremely humid regions (tropics, rain

forests) so much rain that

– CaCO2 and SiO2 are completely leached– silicate minerals are completely altered– In Horizon B are insoluble oxides of Fe, and Al

Hardpan– limonite (Fe-hydroxide)– bauxite (Al-hydroxide)

poor for cultivation due to laterite and thin soil


Tundra soil

Arctic Regions composed of

– sand and clay, some humus, and Permafrost Layer

permanently frozen ground


Permafrost Problems

Frost Heaving - pushing of mounds of soil upward due to pressure exerted by ice, resulting in uneven, hummocky or undulating surface

Stone polygons Engineering problems


Rainforest Problem 1945 - 1990

– greater than half of Earth’s tropical rainforests cut partially for timber partly for agriculture

– this is deforestation Once vegetation is removed leaching

produces poor laterite soil– limited crop production (few years), then

wasteland


Deforestation of the Tropics

continues at a rate of 7 million hectares per year

nancy van wagoner, acadia university soils nancy a. van wagoner acadia university

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