What Is Soil? Chapter 1

Soil Analysis Ch Why Study Soil Science?  what we call soil is also known as the ‘lithosphere’  it plays an significant role in environmental science and chemistry  that is why you are learning about this non-renewable resource

Soil Analysis Ch13 Exercise 1.1(a)  What is meant by the term ‘soil’? the layer of minerals and organic matter, in thickness from centimeters to a meter or more, on the land surface

Soil Analysis Ch14 Exercise 1.1(b)  What are the three main functions of soil? 1. support plants, make it possible for plants to grow 2. regulate and partition water flow through the environment 3. buffer environmental change (from DECC, )

Soil Analysis Ch15 Other soil functions  provides a physical matrix, chemical environment and biological setting for water, nutrient, air and heat exchange for living organisms  controls the distribution of rainfall or irrigation water to runoff, infiltration, storage or deep drainage  regulates water flow affects the movement of soluble materials such as nutrients or pesticides

Soil Analysis Ch16 Soil functions cont.  regulates biological activity and molecular exchanges among solid, liquid and gaseous phases  affects nutrient cycling, plant growth and decomposition of organic materials  acts as a filter to protect the quality of water, air and other resources  provides mechanical support for living organisms and their structures

Soil Analysis Ch17 Exercise 1.2  Why do you need to know about such things? to classify soil types to determine soil health and fertility for rehabilitation sites to analyse and monitor pollutants in contaminated soils to determine if environmental ‘crimes’ have been committed (pollution events) to obtain, store and transport samples for analysis

Soil Analysis Ch The components of soil  Soil is an extremely complex and variable material, but all soils have four non-living components; Inorganic minerals Organic materials Water Soil gases

Soil Analysis Ch19 Inorganic minerals  A simple reminder… Generally does not involve carbon except… Carbon dioxide equilibria (CO3/HCO3) Remember ions – cations, anions? Mainly Silicon (Si) based chemistry PLUS the rest of the periodic table Heard of ‘ores’?

Soil Analysis Ch110 Organic materials  These are the ‘natural’ kinds; Detritus Breakdown of plant matter Humus material – mainly carbohydrate based, but also proteins and tannins The empirical chemical formula for this type of material is {CH 2 O} Note the lack of N,P & S – the formula is not ‘real life’

Soil Analysis Ch111 Water  Obvious…isn’t it? Soon to discover water is not what it seems Issues include availability, transport, storage, and access Aqueous chemistry important, such as pH

Soil Analysis Ch112 Air (soil gases)  not really air! Well, it may be, but not likely Air is ~78% N 2, ~21% O 2, and ~350ppm CO 2 plus trace gases Soil gas is extremely variable, but due to the bacterial oxidation (or reduction) of {CH 2 O}, exhibits higher CO 2 levels (or CH 4 if reduced)

Soil Analysis Ch113 So, what is a typical soil?  no such thing as a typical soil hard to classify a soil type the composition of the main components is so variable can only generalise about what to expect

Soil Analysis Ch114 ‘Typical’ soil composition

Soil Analysis Ch115 But what if…?  the material you are looking at, doesn’t have all four components?  it isn’t soil, and may be one of the individual components  there is also something called regolith: what lies between the upper soil and the lower bedrock

Soil Analysis Ch Rock types  There are three major rock types; Igneous Sedimentary Metamorphic  vary in composition (especially %silica) but mainly their formation  weather to eventually form the mineral content of soils

Soil Analysis Ch117 Rock formation

Soil Analysis Ch118 Common rock types

Soil Analysis Ch119 Rock weathering  soils which are derived from a type of rock tend to have that type of acidity  eg granite-derived soils will have a lower pH than those derived from basalt.  the minerals that form these rocks, chemically change on breakdown  new minerals form through chemical reactions occurring in the soil  the primary rocks and minerals play a critical role in determining the type of soils that form

Soil Analysis Ch Physical Components of Soils  based on particle size  affect properties such as texture Soil Clay (< 2 um) Silt (2-50 um) Sand (>50 um)