Several processes are involved in soil
formation and may, to some extent, affect the
soil profile. These processes are:
Eluviation
It is the mechanical translocation of clay or
other fine particles down the profile.
(more content follows the advertisement below) A D V E R T I S E M E N T
Illuviation
It is the accumulation of the washed down
(eluviated) material in the lower horizons of the
soil profile.
Cheluviation
It is the downward movement of material,
similar to leaching but under the influence of
organic complex compounds.
Leaching
It is the removal and downward movement of
material from a horizon in solution.
SOIL HORIZONS
Horizons are soil layer that are approximately
parallel to the soil�s surface. Each horizon is
different from other. Boundaries between
horizons range from indistinct to abrupt and
clear. Horizons are formed because of
differences in the degree of depth, amounts of
humus accumulated, translocation of colloids
by water and loss of colloids. Capital letters,
A,B,C,E,O and R are used to designate master
horizons. Lowercase letters are used as
suffixes to indicate specific characteristics of
the master horizon.
SOIL FERTILITY AND PLANT NUTRITION
Plant nutrition is the process of absorption
and utilisation of essential elements by plants
for growth and reproduction. Most plants need
at least 16 essential elements � carbon,
hydrogen, oxygen, phosphorus, potassium,
nitrogen, sulphur, calcium, iron, magnesium,
boron, manganese, copper, zinc, molybdenum
and chlorine. Plants utilise hydrogen, oxygen
and carbon from air and water. Nitrogen,
phosphorus and potassium are absorbed from
soil and fertilisers. Chlorine, copper, boron,
iron, manganese, molybdenum and zinc are
micronutrients that are absorbed in lesser
quantity. Nitrogen is most often the limiting
element in plant growth. It is utilised by plants
as ammonium or nitrate. The fertility of soil
depends upon the presence of essential
elements as well as the organic matter in
sufficient amount.
SOIL TAXONOMY OR CLASSIFICATION
Soil taxonomy or classification of soils, is the
grouping of soils on the basis of their
morphology (texture and structure),
appearance, form and fertility. The first
complete US taxonomic classification was
published in 1938 and modified in 1949.
Although the US system has application
worldwide, many countries � France,
Canada, China, India, Brazil and Russia use
their own systems. The present US
classification organises all soils into 11 orders,
54 sub-orders, 238 great groups, 1,922
subgroups and then families and series.
In traditional classification, the major
divisions of soil are Zonal, Intrazonal and
Azonal.
Zonal Soils
These soils reflect climate and vegetation to a
large degree, hence, their name. They are
formed on well drained sites on non-extreme
parent material. Polar desert soils, Podzols,
Brown earths, Prairie soils, Chernozem,
Chestnut soils, Brown and gray semi-arid
soils, Grumusols, Red earths, and Lateritic
soils fall under zonal category.
Intrazonal Soils
These are well developed soils formed where
some local soil forming factor is dominant.
Soils in this category belong to four main
groups, namely saline, hydromorphic,
calcareous and organic. Each group consists
of a variety of soil types.
Azonal Soils
These have poorly developed profiles because
some factor of soil formation has inhibited soil
formation. Lithosols, alluvial soils and dry
sands fall in this category.
|
AKHAND PRATAP SINGH
