Pakistan is a land of great contrasts. The northern part is wrapped in snow-clad mountains; in the east lie the desert areas of Cholistan and Tharparkar; the central part comprises the fertile Indus Plain; the west and the north-west covers intermountain valleys of Balochistan and the NWFP, and in the south lies the coastal belt of Balochistan and Sindh.

Climatically too, the country has great variations in temperature and rainfall. The temperature ranging from less than freezing to over 45C and rainfall varying from 100mm in southern areas to more than 1000mm in northern mountain ranges. The fertile lands of Indus plain and intermountain valleys of the NWFP and Balochistan and the waters of river Indus, its tributaries and various other rivers and nallahs, flowing in the mountains areas, are the sources of great natural wealth for the burgeoning population of the country.

As we know, Pakistan is an agricultural country and canal irrigation is its lifeblood. However, these canal water resources are not sufficient to meet crop water requirements. To overcome the deficiencies, groundwater resources have been extensively exploited. About 250,000 public and 350,000 private tubewells are working in various irrigated parts of the country. The water quality ranges from good, marginal to hazardous. Due to inefficient water management practices and brackish groundwater, a good deal of agricultural land has gone out of production due to water logging and salinity.

Agriculture is the backbone of Pakistani economy, and over 40 per cent of the irrigation supplies at farms are provided by the groundwater. As such groundwater is quite important for development. The preservation in terms of quantity and quality of water is important for sustained irrigated agriculture. It is also used extensively for domestic and industrial purposes. The groundwater operations in the country were carried from 1954 to 1965 in all the provinces of Pakistan and still it is in use for the growth of crop plants on a large scale.

The quality found in various aquifers is greatly variable which is due to the complex geology and the variable topographic, climatic and hydrological conditions. The salinity concentrations in the Indus plain vary from less than 500ppm in good quality groundwater areas in the Punjab to over 70,000ppm in the Indus delta. The Indo-Gangetic plain is comprised of 300,000sq miles of the most fertile land. Groundwater is being used in Pakistan for agriculture on a large scale since the early sixties. For irrigation purpose it is being obtained not only from fresh areas, but also from marginally saline groundwater areas. When this water is applied to crops, water is taken up by the plants, while the salts are left in the soil. As such, tubewell irrigation mobilizes the salts lying down below the groundwater surface and spread them on the surface, from where they are again leached to groundwater. This process when repeated for a long time, without the mechanism of export of salts from the soil results in increasing the salinity of groundwater, which in time shall change from fresh to marginal and from marginal to hazardous with the passage of time.

Its application with heavy laden salts has deteriorated the situation even more. At present, it is estimated that about 120 tons of salts per acre is being added with irrigation every year to the agricultural land. These lands, which are irrigated with brackish tubewell water, develop hardpan/low permeability and accumulate salts on the surface. The Indus Basin represents an extensive ground water aquifer covering a gross command area of 16.4 million hectares. Water table was well below the surface and aquifer was in a state of hydrological equilibrium before the development of canal irrigation system a century ago. When canal irrigation system was introduced, percolation to the aquifer was increased in irrigated areas of the Indus Basin resulting in the menace of water logging and salinity. Groundwater contributed around 12BCM during the pre-storage period, which constituted 11 per cent of the total water available for agriculture. During the past storage period, the estimated recharge to the groundwater in the Indus Basin is 56BCM, of which 36BCM covers areas of usable groundwater. Groundwater use has increased significantly in the last three decades.

The total annual groundwater potential in Pakistan is estimated at 68BCM: about 80 per cent of it in Punjab and 30 per cent in Sindh is suitable for agriculture. Since most of the easily exploitable surface water resources have already been tapped, the future demand of water will have to be met largely through additional storage, better conservation and efficient use of water.

Continuous additions to groundwater from an irrigation system, along with deep percolation from crop lands, have resulted in rising groundwater levels. Lowering of water table to some degree was achieved through public and private tubewells, but salinity developed in normal soils as a result of irrigation with poor quality tubewell water. The result is reduction or stagnant yields of crops. Other causes of low productivity include inadequate use of fertilizers and micronutrients, poor soil management and tillage practices, inadequate and shallow rooting depths. Water logging and salinity have adverse impact on crop yield. All the major crops such as cotton, rice, sugarcane, wheat, etc., are badly affected by groundwater qualities.

Owing to the heat of sun, water is drawn to the surface of the field by capillary action and then it evaporates, leaving behind in the top soil the soluble salts it contained. Without drainage, the water table can eventually rise to the ground surface or in the top 30cm of the soil profile. Due to this, the profitable cropping becomes difficult and the land is abandoned or at least reverts to low grade crop productivity.