WHAT IS SOIL?
A universal definition of soil is not possible as a result of the complexity of soil.
The definition of soil depends upon how you use soil and how you interact with soil.
A geologist may consider soil as a weathered rock or par
TOPIC 5A: SOIL WATER
Water is ubiquitous, unique and an anomalous compound. The ubiquitous nature of
water is demonstrated by its tendency to occur everywhere, and in the composition of all living
things which are made up, almost entirely, of
Topic 4: VOLUME CHANGE IN SOILS
Changes in volume in clay soils occur because the forces of attraction between water and
clay particles are much greater than comparable forces in sands. Thus, if one extracts
water from a saturated clay no void is created
Topic 2: SOIL PARTICLE SIZE DISTRIBUTION
The liquid and gaseous phases of the soil system vary in time (temporal variation), while the
solid phase can be regarded as permanent in time (though not in space). It is the solid phase
that we readily identify w
TOPIC 5B: WATER MOVEMENT IN SOILS
Water in soils is rarely static; water additions from rainfall or irrigation and water losses from
evaporation, transpiration or drainage are occurring most of the time.
Water moves from a region of high potential to a re
Soil aeration - that part of the gaseous cycle involving the interchange of CO2 and O2
between living organisms, soil and the aerial atmosphere. This exchange is necessary
because O2 is required in the soil for respiration which in turn affe
INFILTRATION OF WATER
Infiltration is the process of water entry into the soil by downward flow through the
soil surface. The rate of infiltration, compared to the rate of supply of water to the soil
surface, determines the magnitude of water stored in th
Soil temperature is one of the more important factors that control microbiological activity
and the processes involved in the production of plants. It is a well-established fact that the
rate of organic matter decomposition a
Topic 8:SOIL STRUCTURE
The primary particles of sand, silt, and clay do not exist as individual particles in soil,
but are arranged and bound together to form secondary particles, or aggregates. (The
exceptions to this are structureless soils
Topic 7: AVAILABILITY OF SOIL WATER TO PLANTS
Plants use lots of water. Between 400 -1000 g of water is used for every gram of dry
matter that plant produces. Using an average value of 500 g of water per gram of
dry matter, it can be shown that, to produc
TOPIC 3: PHYSICO-CHEMICAL PROPERTIES OF CLAY
As mentioned previously, the term clay has several connotations in soil science.
The smallest size range of primary particles found in the soil (<2m).
A clay soil is a textural class of soil containing a high