Soil can be defined as a thin layer of the earth's
crust, which serves as a natural medium for the growth of plants. Soil,
though considered as a non-living thing, acts as a home for various
living organisms from small worms and insects, to reptiles, etc. Thus,
the soil is an environment of its own. For a healthy-ecosystem, healthy
soil is important. The physical properties of any kind of soil largely
determines the manner in which it can be used. Properties like water
holding capacity, permeability to water, aeration, plasticity and
nutrient supply ability, are influenced by the size, proportion,
arrangement and mineral composition of the soil particles.
In Holy Quran, there is a world Ard (AI-Ardh), which
means earth, ground, land or soil; Earth is a planet on which we live,
with the five continents, oceans, seas, lakes, mountains, valleys, great
deserts, glaciers, rain forests, savannas, prairies, rich meadows and
fertile plains. Its centre is boiling lava, while its surface is covered
with a thin layer of disintegrated organic and non-organic solid
materials. From this earth, five soil materials are developed. Soil is
the main component of the earth. Soil is defined as a 'natural body,
engendered from a variable mixture of broken and weathered minerals and
decaying organic matter, which covers, the earth in a thin layer and
which may supply, when containing, the proper amounts of air and water,
mechanical support and in part sustenance of plants. Soil is considered
as a natural body with three major components, solid, liquid and
Some major soil groups are as follows:
These soils vary in depth from shallow to deep. They are highly
argillaceous, very fine grained and dark, containing a high proportion
of calcium and magnesium carbonates. But they are poor in phosphorus,
nitrogen and organic matter.
This type of soil differs in constituency from drifting sand to loam and
from fine silt to stiff clay. This is also the most important soil group
contributing in a major extent to agricultural wealth.
RED SOIL: This
is the most predominant type of soil found in the world. These soils are
rather shallow, very open in texture, having a pH ranging from 6.6 to
8.0 and are generally poor in nitrogen, phosphorus and humus.
These soils are specially well developed on the summits. Though poor in
lime, magnesium and nitrogen they are rich in plant nutrients and
the soil particles are very fine grained and fine textured, the quality
of retaining water is more and hence the water infiltration capacity is
SAND: This is
found in coastal and river bed areas. These soils are very permeable and
drain well, but are less water retentive.
PROBLEMS ARISING DUE TO SOIL LOSS:
Deforestation leads to loss of top soil, soil erosion and nutrient
leaching. It takes about 2,000 years for the top soil to develop. Due to
deforestation, on open, bare land, soil gets dissipated or carried away
by monsoon rains and deposited in rivers, tanks and ponds, thus leading
to silt formation, thereby reducing their water holding capacity. The
exposed poor soil in agricultural lands makes it unfit for cultivation;
soil erosion occurs due to wind and rain. Prolonged soil erosion may
lead to formation of gullies and may lead to land slides.
In humid regions where rainfall is high, the continued leaching of soils
results in the replacement of calcium, magnesium, potassium and sodium
ions by hydrogen ion, leading to the formation of acidic soils. Lime
application neutralizes to some extent the acidity in the soil. Crops
like millets, oats, peas and soybeans, can tolerate moderate acidity and
trees like Derris indica, Gliricidia and Tamarind can be grown in these
In Pakistan, 6.3 million hectares of land are saline in nature. This
soil contains toxic concentrations of soluble salt in the root zone.
Because of the white encrustation due to salts, the saline soil is also
called white alkali. The salinity may increase due to a rise in the
water table, water-logging in the root zone and sea coast irrigation.
Excess soluble salts like chloride, sulphate, sodium and calcium will be
present. Tree species like Azadirachta indica, Prosopis julliflora,
Terminilia arjuna and Albizia lebbeck can be grown in these soils. While
planting, ridge-trench method, sub-surface planting and planting in
furrow irrigation channels would help to reduce the toxicity of salts.
ALKALINE OR SODIC SOILS:
These soils do not contain any neutral salts. Because of high alkalinity
resulting from sodium carbonate, the surface soil appears discoloured
and black. Such soils have a very low infiltration rate. If the soil
texture is heavy, gypsum can be added. Silt and rice husk can also be
added to improve the texture. Trees like neem, Albizia lebbeck, Derris
indica, Subabul, Prosopis and terminilia arjuna can be planted.
There are around 16 micro and macronutrients needed for the healthy
growth of a plant. During each harvest, the soil's fertility will keep
progressively reducing. To protect the fertility of the soil, it has to
be tested each time after harvesting. A careless application of
fertilizers will only further deplete the soil fertility. It is also not
advisable to apply micro and macronutrients simultaneously into the
soil. Mixed cropping would help to balance the nutrients in the soil.
Although, the problems of soil management vary according to the soils
and their situations and the climatic conditions, these are fundamental
factors, which govern the choice of soil management practices. The
productive capacity of the soil should be improved and maintained by
providing adequate organic manure and plant nutrients.
SOIL TEST: For
maximum production and rational soil management, knowledge of the soil
fertility status and the physical properties is essential. Soil testing
is one of the methods of determining the fertility status of the soils,
so that recommendation in regard to deficient nutrients or soil
amendments can be made.
COLLECTION OF SAMPLES:
It is advisable to remove all leaf litter and debris from the top soil
and using a soil tube, an auger, a spade or a pick-axe, to dig the soil
in a V shape up to a depth of 10 cm and then collect the sample. The
soil should be removed from the centre of the land, but manure filled or
compost areas have to be avoided.
There are 16 micro and macronutrients essential for
plant growth, i.e. nitrogen for leaves, stem growth, seed development;
Phosphorous for roots to-spread and absorb water; Potassium for
protection from disease, pest resistance, and compensating
evapotranspiration; Iron for preparing chlorophyll and for energy
development and transfer; Zinc growth stimulator; manganese for
absorption of C02 and for transfer of nitrogen; Copper for preparation
of primary protein; boron in cell formation and division; molybdenum to
absorb nitrogen and to resist excess micro-nutrients; sulphur for
chlorophyll and root development; Calcium in cell development and for
transfer of food; magnesium for protein preparation — as an enzyme
catalyst; other nutrients such as carbon, hydrogen, oxygen and chlorine
too play vital roles in plant growth.
Land is a very valuable but limited resource, as the population
increases rapidly. Many highly urbanized cities are faced with acute
space problems, as in Karachi, Calcutta or Bombay. Besides the limited
availability of land, 175 million hectares of land are becoming less
productive every year. Pakistan loses 20 tons of topsoil per hectare in
a year due to floods, rainfall and deforestation. 20 % to 50 % of lands
under irrigation can go out of cultivation at this rate because of water
logging and salinity. The scenario of desertification is compounded by
pollution which includes indiscriminate discharge of industrial
effluents on land and into water bodies; an increase in the use of
fertilizers for agriculture; open defecation by animals and human
beings; accumulation of solid waste; this is a major problem in
developing countries like Pakistan, where the garbage and refuse
products are not degraded and radioactive substances from nuclear plants
are released into the soil.
MAJOR SOIL POLLUTANTS AND THEIR EFFECT ON HUMAN
Arsenic occurs naturally chronic poisoning leads to
loss of appetite and weight, diarrhea, alternating with constipation,
gastrointestinal disturbances, peripheral neuritis, conjunctivitis and
sometimes skin cancer. Cadmium mining, metallurgy chemical industry and
electroplating lead to chronic poisoning and affect the proximal tubules
of the kidney, causing formation of kidney stones. Lead smelters storage
battery lead poisoning can lead to severe mental retardation or death.
Mercury industrial wastes and methylmercuric compounds are much more
toxic than other forms of mercury, causes neurological problems and
damages renal glomeruli and tubules. Cyanides waste from heat treatment
of metals, dismantling of electroplating shops, etc. rapid death may
follow due to exposure to cyanide as a result of inhibition of cellular