Soil salinity is one of the important factors affecting agricultural production of Pakistan


By Dr. S.M. ALAM
NIA, Tandojam.

Nov 03 - 09, 2003




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).



CAUSES: 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.