Pakistan has the largest single contiguous gravity flow system in the world consisting of three reservoirs (Tarbela, Mangla and Chasma), 19 barrages, 12 huge inter-link canals, 59,200km of irrigation canals and over 1.6 million km of water courses. The system is supported by 44maf of groundwater from nearly 700,000 tube-wells. Of the total cultivated area of 21.9 million hectares of the country, 80 per cent is irrigated.

However, the increasing population and declining water availability due to mismanagement have already created a drought like conditions. It may still become worst if appropriate measures are not taken well on time to meet the existing and future expected irrigation deficiencies. Some of the required measures to increase irrigation efficiency are as under:

River system losses: The average annual flow of river water is 144maf, since the completion of Tarbela Dam in 1976. Out of which 106maf is diverted to canal heads and about 38maf is going annually to the Arabian Sea. Keeping in view the future survival another reservoir of 6-8maf may immediately be constructed at the earliest.

Again, the present seven water development projects, including raising of Mangla Dam by 30 feet will increase water storage capacity by about 5maf during the next 5-7 years that may bring additional 0.78 million hectares of land under cultivation in all the four provinces. But the storage capacity of Tarbela, Mangla and Chasma dams may further decrease considerably during this period thus, seriously negating the impact of these new projects unless alternate planning for the construction of a new reservoir is not made immediately to utilize the huge annual loss of water to the Arabian Sea.

Conveyance losses: Not all of the water (106maf) diverted to canal heads is available for crop production due to conveyance losses. A recent estimate by the agriculture engineers shows that conveyance losses at the main canals and their branches are 25 per cent, at sanctioned watercourses 20 per cent, at farmers watercourses 15 per cent, and at irrigation fields 8 per cent with a total loss of 68 per cent or nearly 72maf. This colossal loss is not only higher than the total original storage capacity of 17.1maf of Tarbela, Mangla and Chasma reservoirs, but also much higher than the annual water loss to the Arabian Sea.

These conveyances losses are attributable to the surface evaporation, seepage from unlined canals, poorly designed and maintained watercourses, defective irrigation practices, inequity of water distribution and lack of precision land levelling. As a result, the crop yields are 50-80 per cent below their demonstrated achievable potential at the farmers fields.

Although some of the water lost during conveyance returns to streams and aquifer where it can be tapped again, most of it is lost and is not available for the crops. The policymakers and planners should develop a sound irrigation programme for increasing irrigation efficiency by regular desilting of canals, distributaries and minors; redesigning and improvement of watercourses; post-improvement care by community participation approach; and precision land levelling through laser technology.

There is a serious lack of coordination between different departments related with irrigation system, especially at the field level. Their linkages be strengthened and given annual targets for increasing irrigation efficiency. Their progress be monitored and evaluated and strict disciplinary action be taken against those responsible for mismanagement, corruption, inefficiency and below the target achievement.

Drip irrigation: It is one of the technique to improve irrigation efficiency, thus saving water and protecting land. It consists of a network of porous or perforated piping usually installed on the surface or below ground that delivers water directly to the root zones of crops.

This technique keeps evaporation losses low at an efficiency rate of 95 per cent and reduces water use by an estimated 40-60 per cent compared with the gravity system. In 1971, drip irrigation systems were used only on 56,000 hectares worldwide mostly to supply water to vegetables and fruits.

By 1991, it has increase to 1.6 million hectares and that has further increased considerably since then. It is now widely used in the US, Australia, Israel, Mexico, New Zealand, South Africa and other countries. In Israel, drip irrigation is used on 50 per cent of their total irrigated area.

Drip irrigation system has great potential in arid and semi-arid regions of Pakistan such as Balochistan, where indiscriminate expansion of authorized and unauthorized tube-wells and over-irrigation to high value crops like orchards and vegetables have lead to serious over-mining of groundwater aquifer and its consequent lowering by two or more meters annually.

For example, there is now no groundwater potential in Quetta, Pishin, Mastung, Mangochar and Pishin Lora because of over-mining of these basins, while Zhob, Qilla-Sufaid, Nari river, Hamun-e-Lora and Kachi plains still have limited groundwater potential. The drip irrigation research by the FAO in Balochistan has already established beyond doubt that by this system not only overuse of groundwater is checked, but the yields of orchards are also significantly increased. So the use of drip irrigation should form part of mass communication and education programmes in the limited surface and groundwater areas of the country.

In Thal, Cholistan, Thar and Chagai-Kharan deserts where water is a limiting factor, fruit trees like date palm, zizyphus species, pomegranate, guavas and other fruits capable of growing under desert environments may be planted in 60 cubic meter pits dug at 6 metre apart in a square. The pits can be irrigated by using discarded plastic infusion/drip sets from the hospitals. Each drip set be filled with water through a slit made at the closed end of the bag tied to a pole fixed near the pit of the planted fruit sapling. Each pole may have one to three suspended infusion sets depending upon the availability of water, need and age of plant and season of irrigation.

Each morning water should be poured into the bags and it flows through each emitter to be properly regulated. Covering each pit with a plastic sheet will further reduce evaporation losses. The housewives of desert dwellers can also grow vegetables in 33x1.5 metre plots by using discarded plastic infusion sets as is being successfully done by the housewives in the adjoining Rajisthan desert of India. The technique is called as “desert or arid kitchen gardening”.

Sprinkler irrigation: In this method water is applied to the surface of the soil in the form of a spray in a manner similar in natural rainfall. Spray is developed by flow of water under pressure which is obtained by pumping. This method can be applied to all crops except rice and jute. It is generally applied to high value crops such as orchards, vegetables, nurseries, etc.

It can be used on undulating soils, thus reducing cost of land levelling. More land becomes available for cropping as field channels, furrows or corrugations, ridges or borders, etc., are not required. The greatest advantage of sprinkler irrigation is to utilize water equivalent to the water requirement of a crop and application of excess of water which may cause deep percolation and water logging can be avoided.

This system considerably increases irrigation efficiency and comprises four types such as permanent, semi-permanent, portable and semi-portable.

Low energy precision application (LEPA): This system offers considerable improvement over conventional sprinkler systems that spray water into the air. Unlike these sprinkler systems, LEPA method delivers water to the crops from drop tubes that extend from sprinkler’s arm. When applied together with appropriate water saving farming techniques, this method can achieve efficiencies as high as 95 per cent.

Since this method operates at low pressure, the energy cost drops by 20-50 per cent as compared to the conventional sprinkler systems. Farmers in Texas, who have retro-fitted conventional sprinkler systems with LEPA, have reported that their yields have increased by 20 per cent and their investment cost was recovered within one to two years.

Saline/brackish water irrigation: The use of saline or brackish groundwater for irrigation with new irrigation techniques has been reported in many countries such as Turkey, India, Israel, etc. It should conform to certain norms before its use. In Pakistan 44maf of groundwater from nearly 700,000 tube-wells is used for irrigation and nearly 70 per cent of which varies from marginally saline to highly brackish.

Its use not only decrease crop yields but also increases soil salinity. Therefore, to increase the irrigation efficiency of such saline/brackish groundwater, the well established Gypsum Technology, Sulphurous Acid Generator Technology developed by a US firm and Ristech Bio-Technology introduced by a UK firm for amelioration of saline/brackish groundwater be tested on the farmers fields. Whichever is more economical and efficient should be adopted for increasing the irrigation efficiency of its saline/brackish groundwater.

Sea water: Increasing water requirements for domestic, agricultural and industrial uses make it essential for maximum utilization of our available water resources. There is huge resource of saline sea water along our 1,050km long coast along the Arabian Sea. But it cannot be used either for drinking or agriculture unless desalinized. Desalinization of saline sea water has been practised regularly for the last over 50 years in 120 countries in the world.

The planners should develop a strategy to test latest desalination techniques such as the multistage flash technique, vapour compression technique, multi-effect distillage technique, etc., to meet the impending challenges of future water scarcity. Again, there are highly salt tolerant plant species that can grow with double the strength of saline sea water on well drained sandy coastal soils such as Atriplex species. Cattle, sheep, goats and burrows feed well on them. Another candidate crop is Districhilis palmeri which has large wheat like grains containing 9 per cent protein.

Irrigation by urban waste water: A number of countries divert treated urban sewage water from towns and cities onto the nearby farms growing vegetables and fruits.

In 1998, nearly half a million hectares in 15 countries were being irrigated with treated urban waste water, often referred to as brown water. Israel has the most ambitious brown water programme. In Mexico, city treated urban water is used for growing alfalfa. Similarly, one-third of vegetables grown in Asmara in Eritrea are irrigated with treated urban waste water.

In Indian city of Calcutta, much of its raw sewage water is diverted into a system of natural lagoons where fish are raised. The city’s 3,000 hectares of lagoons produce 6,000 tons of fish annually for urban consumption.

In Pakistan untreated sewage water is used for production of vegetables and fodders in the vicinity of cities and towns. However, crops raised from such sewage water are not safe for human consumption from hygienic point of view.

Nevertheless, there is a good potential of treating sewage water and recycling it for human consumption or using it for increasing irrigation efficiency as is being done in several countries of the world. The policymakers should also seriously consider to exploit this potential for increasing irrigation efficiency.

Conservation agriculture: Conservation agricultural practices can significantly increase irrigation efficiency. For instance, in rice-wheat cropping system in Pakistan, sowing of wheat with zero-tillage drill increased irrigation efficiency by 20 per cent, decreased cultivation cost of wheat by about 82 per cent, reduced energy consumption by 81 per cent and increased yield by 15 per cent.

Similarly recent research on bed-furrow plantation of wheat and cotton increased irrigation efficiency up to 30per cent. Again, changing of cropping pattern can have significant effect on water saving. For instance, spring planted sugarcane crop requires 64-80 acre-inch of water per acre (0.4 hectare), while autumn cane crop requires 80-100 acre-inch of water per acre under the conditions obtaining in Pakistan.

If instead of sugarcane, cotton-wheat or maize-wheat cropping system is adopted, it will require only 44 and 41 acre-inch of water, respectively. Thus, it will not only increase irrigation efficiency, but will also enable to take two crops as against a single sugarcane crop.

Again, where sugarcane can be replaced by sugar-beet, it will require only 19-22 acre-inch of water as against 64-80 ace-inch of water required for spring cane and 80-100 acre-inch of water for autumn cane crops. Similarly, if wheat, onions or other small duration crops are inter-cropped in sugarcane, it will enable to take these additional crops without any extra irrigation or any adverse effect on the yield of sugarcane.