The problem of salt in agriculture is not new.
Worldwide experts estimate that salinity affects productivity on about
80 million hectares of cultivable land — just — about a total land
area of a country the size of Pakistan-predominantly in developing
countries having hot and dry climates. The problem arises when salt is
left behind in the soil as water passes back into the air atmosphere
through the processes of evaporation and plant transpiration. In areas
with good rainfall and effective drainage systems. The soluble salts
change in composition and concentration as water carries them away
eventually, to the seas. But in part of the world having little rainfall
and restricted drainage, the salts cannot easily be transported. They
accumulate in lowlands, or in the groundwater below them. Of the nearly
21 million hectares cultivated lands in Pakistan, 1.5 million are
salinity affected. Every year, 0.2 to 0.4% of the land is rendered
infertile due to salinity.
A) SALINE SODIC SOILS: have
a high Na content alongwith other salts (most saline soils in Pakistan
belong to this category).
B) SALINE SOILS:
white salts can be seen on the surface of the soil.
C) SODIC SOILS: high
sodium concentration dissolves organic matter, turning the soil black
(very difficult to reclaim).
Nature's own geographical and
geological processes are a major contributor to salinity. Experts say
that more than 30 million hectares of salt-affected land arise from
natural causes, aridity, and high rates of evaporation. In many cases,
problems are exacerbated by the loss or destruction of natural
vegetation from animal grazing or the search for cooking and heat. Most
saline lands, however, are in or near areas where irrigation is the
backbone of farming, predominantly developing countries. Lack of good
drainage is a major contributor to salinity. So is seepage from
irrigation systems and drainage fields, which can lead to a loss of
nearly half of the water. Gradually the groundwater table rises,
bringing salts to soil layers where craps get nutrients. The result is
stunted or dead plants. As surface waters evaporate' the fields become
white encrusted, salt-capped wastelands. Farmers abandon them and
agricultural economies suffer.
Rivers carrying soluble minerals to low lying areas.
Rising water table causing salts to rise to the surface evaporate and
form a crust. Insufficient natural drainage or ineffective man made
drainage systems. Water seepage due to poorly humid canals. Excessive
pumping of clear groundwater to coastal areas. Inadequate land leveling
and improper crop rotation patterns.
Soil salinity is one of the important factors
affecting agricultural production of Pakistan, where more than 6.23
million hectares are affected. Soil salinity not only affects plant
growth, but also the soil microorganisms and can therefore enhance or
suppress the incidence of plant infection by these microorganisms.
Salinization and codification of soils are major problems in dry land
farming. The soils in which the electrical conductivity (EC) of
saturation extracts exceeds 4 dSm-1 are classified as saline soils.
Saline soils possess poor physical properties and fertility problems
that adversely affect growth and yield of most crops. The worldwide
occurrence of such soils on 560X106 hectares, emphasizes the need for
efficient, inexpensive and environmentally acceptable management.
These soils can be ameliorated by providing a source
of calcium (Ca2+) to replace excess sodium (Na+) from the cation
exchange sites. The replaced Na+ is normally to be leached out from the
root zone. Amelioration of saline soils with chemical amendments is an
established technology. Some amendments to supply Ca2+ directly to the
soil, which then replaces excess exchangeable Na+, while others help to
increase the dissolution of calcite in saline soils. However, chemical
strategies have become costly for subsistence farmers in developing
countries during the last two decades.
Salinity can be controlled, and lands reclaimed,
though not overnight and not easily or inexpensively. One approach is
constructing good irrigation systems that gradually improve soil
conditions and prevent formation of waterlogged and unproductive fields.
Systems need to apply slightly more water than the crop needs, to
promote leaching, and then drain and catch groundwater so that it can be
recycled for agricultural or industrial uses. Unfortunately, poor
irrigation practices often promote rather than control salinity, and
engineered drainage systems extending over large areas of land are
financially out of reach for most countries.
Leaching or removing salts and flushing the salts.
Using tubewells for surface, subsurface and vertical drainage, leveling
land cultivating crops on raised beds, through sowing seeds and high
density planting. Using gypsum for replacing sodium. It increases water
holding capacity and aeration.
Biosaline agriculture suiting salt-tolerant plants to
soil and water conditions may offer a more affordable alternative,
though not necessarily an easier one. It depends upon good irrigation
practices, especially where the groundwater already has higher than
normal salt concentration. And it takes years of research and testing to
match the right plants with the right soil and water conditions, then
maintain the ecological balance for sustainable agricultural production.
Cultivating salt-tolerant crops, barley, bermuda
grass, cotton, kallar grass, sugarbeet, oats, rapeseed, rice, rye
soybean. Cultivating salt-tolerant trees-kiker, sufaida, amrood, ber,
khajoor, jaman, dhancha and jantar. Amendment costs have increased
because of increased use by industry and reductions in government
subsidy to farmers for their purchase. Alternatively, where both
irrigation water and drainage are adequate and the soils are calcareous,
techniques for amelioration can be based on the use of crops tolerant to
soil salinity and sodicity levels.