2. Land as a resource
Usar land
Formation of usar land
Reclamation of usar
land
3. Land is the basic and most important resource
to the mankind. All agricultural, animal and
forestry production depend on the productivity
of the land.
Land is considered as an important resource as
it provides habitation to a wide variety of flora
and fauna. It is used by human beings for
various purposes such as agriculture, forestry,
mining, building houses and roads, and setting
up industries.
4. The land resource is limited as the total
geographical area is fixed. The amount of land
and land-based resources is, then finite. Land is
therefore, scarce in supply. Under these
conditions, every part of the land is important
for us and for the nation.
5. Out of the several problems that limit the
economic utilization of land resources in India,
the problem of usar lands (Sodic and Saline) -
the so called salt -affected soils is of great
concern.
Deforestation, Excessive use of pesticides and
chemical fertilizers,water-logging etc are few
causes of land degradation.
6. These soils have developed in areas with
dry climatic conditions (in areas having
a little more rainfall than the areas of
desert soils) accompanied by lack of
proper drainage. In this situation, salts
of sodium, calcium and magnesium are
deposited on the upper layer of the soil
by capillary action.
Usar land is defined as that land where
the vaste patches of white efflorescence
salt called ‘Reh’.
7.
8. In India alone, about 7 million ha of the
cultivated land are affected by sodicity
and salinity. Nearly 35 per cent (2.5
million ha) of usar lands are sodic,
occurring in parts of the Indo-Gangetic
plains. In Haryana, it is about 0.50
million ha. Nearly 65 per cent (0.33
million ha) of the usar lands are sodic,
occurring in the Indo-Gangetic plains
with mean annual rainfall of 550-1000
mm.
9. These soils are also formed when saline water
spreads on the land at the time of high tide in
coastal areas. Also, seawater intrusions in the
deltas promote the occurrence of saline soils.
Salinization also occurs because of over-
irrigation (canal irrigation/groundwater use)
and in areas of high water table (as in the coastal
areas of Maharashtra and Tamil Nadu).Salinity
from irrigation can occur over time wherever
irrigation occurs. This is because almost all
water (even natural rainfall) contains some
dissolved salts. When the plants use the water,
the salts are left behind in the soil and
eventually begin to accumulate. Also, excessive
irrigation with dry climatic conditions promotes
capillary action, which results in the deposition
of salt on the top layer of the soil
10. They occur in arid and semi-arid regions, and
in waterlogged and swampy areas. These are
more widespread in western Gujarat, deltas of
the eastern coast and in Sunderban areas of
West Bengal.
11. Other characteristic features:
Because of capillary action, the salts are
sucked up in solution to the surface and form
white encrustations on the surface.
12. Source
The salt efflorescence of calcium, magnesium and
sodium makes these soils infertile.
Saline soils contain an excess of neutral soluble
salts of chlorides and sulphates whereas sodic or
alkali soils contain sodium carbonates/ sodium
bicarbonates.
They lack in nitrogen and calcium and have low
water bearing capacity.
These soils can be reclaimed by improving
drainage, by applying gypsum and/or lime, and
by cultivating salt resistant crops like barseem,
dhaincha and other leguminous crops.
The saline and alkaline soils may occur in any
group of soils.
13. Crops grown: In coastal areas, coconut trees are
found in plenty in these soils. As discussed above,
cultivating salt resistant crops like barseem,
dhaincha and other leguminous crops can help in
reclaiming these soils.
Note: In the areas of intensive cultivation with
excessive use of irrigation, especially in areas of
green revolution, the fertile alluvial soils are
becoming saline. In such areas, especially in
Punjab and Haryana, farmers are advised to add
gypsum to solve the problem of salinity in the soil.
14. The reclamation of sodic soils basically requires
that the excess sodium in the exchange
complex should be replaced with calcium and
exchanged sodium be leached out of the root
zone.
15. Reclamation of Sodic Soil by displacement
process
Reclamation or improvement of Sodic soils
requires the removal of part or most of the
exchangeable sodium ion and its replacement by
the more favourable calcium ions in the root zone.
Soil amendment materials such as gypsum or
calcium chloride directly supply soluble calcium
for the replacement of exchangeable sodium, or
other substances, such as sulphuric acid and
sulphur that indirectly through chemical or
biological action, make the relatively insoluble
calcium carbonate commonly found in sodic soils,
available for replacement of sodium.
16. The application of mined-gypsum in soils and
addition of sulphuric acid to sodic soil surface
reduce soil crusting and improve water
infiltration rate.
Organic matter (straw, farm and green
manures), decomposition and plant root action
also help to dissolve the calcium compounds
found in most soils, thus promoting reclamation
but this is relatively a slow process.
17. These soils can be brought successfully under
cultivation by adoption of reclamation and
management technology. The key to success is the
availability of good quality water and a cheap
source of gypsum.
The main features of the technology are:
The leaching of excess salts from the soil surface
layers.
The supply of adequate quantities of soluble
calcium (like gypsum) to improve the soil
chemically and physically.
18. The application of organic materials (pressmud-a
by product of sugar industry, FYM, green
manures, rice husk, saw dust, charcoal dust,
molasses), either alone or in combination with
other amendments, has also proved beneficial at
several places.
Besides being a source of plant nutrients, these
materials, when decay, liberate large amounts of
carbon dioxide and organic acids which react
with the native calcium carbonate to form soluble
calcium salts and consequently decrease the soil
ESP and pH
19. Use of Saline Water as a Source of
Calcium
Another development in the
reclamation of sodic soils is the high
salt dilution method in which the soil
is leached with saline water in
successive dilutions.
20. For crop other than rice, their irrigation presents
the major difficulty in obtaining their optimum
yields from sodic soils. The low infiltration rates
and the low hydraulic conductivity of these
soils result in a reduced water storage in the
profile.
The root penetration in these soils is restricted
due to a dense and high ESP sub-soil.
21. Fertilization
The low organic matter content and the high pH
impart poor fertility to the sodic soils. Due to low
levels of nitrogenous in these soils, the application
of nitrogen in these soils, the application of
nitrogenous fertilizers is particularly important.
A number of studies have shown that crops grown
in sodic soils respond more to the higher levels of
applied nitrogen than crops grown in non-sodic
soils.
