August 2, 2003

AT THE time of independence, in Pakistan, about 64 million acre feet (MAF) of water was being utilized annually through the irrigation canals. Now with the increase in the number of barrages, link canals and storage dams, water usage has gone up to an average of 106 MAF each year. If the existing situation persists, there is a strong likelihood that the country will not be able to meet its water requirements by the year 2025.

According to a recent estimation, Pakistan’s water requirements by 2015 will shoot up to some 215 MAF with an availability of only 107 MAF and a shortfall of 108 MAF.

In the last 50 years the country’s population has increased five folds with a consequent fall in per capita availability of water. It has also been estimated that the domestic and industrial water usage will increase to a 15 per cent of the available water resource by the year 2025 as compared to the present use of 3 per cent.

It is surprising to find that during 1960s, per capita water availability was 1400 cubic metres, which has currently decreased to a 900 cubic metre, and is projected to go further down to 600 cubic metre per capita by the year 2025. Thus to meet the ever-increasing food and fibre requirements of the massive growing population, an improvement in water productivity is strongly needed.

Though recent rains gave some respite from the extended drought that had reduced freshwater supplies, one cannot deny the need for developing new water resources in Pakistan as well as adopting water conservation measures for judicious use of finite quantity of water. Our agriculture sector is the major consumer of water, and therefore with 97 per cent use up holds great responsibility.

It is a known fact that a great amount of food and fibre is required to meet the demands of our constantly increasing population. Water has the power to bring great benefits, initially from ensuring food security by irrigation and furthermore by generating wealth from cash crops. Thus there is a direct relationship between irrigation and poverty alleviation.

In water scarce areas, there is a great need to shift focus from increasing productivity of land and water. For each drop of water we should aim at increasing the value addition and welfare of our people. In agriculture, this means promoting practices that achieve more output per unit of water consumed. So one of the best ways to free up water for other uses is to improve the productivity of water in agriculture. In this way water productivity will not only be increased for consumed water but also water will be saved which can be utilized to bring more areas under cultivation and irrigate crops that face water deficit specially at critical growth stages.

In this respect, strategies can be classified into two categories: irrigated and rainfed.

Some of the potential agricultural practices that can increase per unit water productivity are given below:

Changing crop varieties: There is a great variability in water requirements for different crop varieties. There is a need to change new varieties that can provide increased yield from each unit of water consumed or the same yields with fewer units of water consumed.

Low water consuming plants should be preferred, which hold great promise and potential for increasing water use efficiency.

Changing cropping pattern: Crop substitution by switching from high to low water consuming crops or switching to crops with higher economic or physical productivity per unit of water consumed. High delta crops, such as sugarcane, rice not only consume a major portion of the available water but also contribute to waterlogging. The high delta crops can be substituted with low delta crops of high market value such as maize, sunflower.

A strategy can be adapted to introduce low delta crops in the cropping pattern where there is water shortage. This will help to generate some income rather than complete failure of high delta crops.

Multiple cropping systems are most effective in improving water and nitrogen resource use efficiency when these systems capture and convert water and nitrogen that would otherwise be lost during non-crop periods of the mono crop culture. By increasing total production, multiple cropping can reduce the land requirement needed for a given quantity of products, while Water Use Efficiency (WUE) may be improved by multiple cropping.

Irrigation strategy: By adopting deficient, supplemental or precision irrigation strategies, rather than flooding, with sufficient water control high water productivities can be achieved. This increases the returns per unit of water consumed.

Innovative irrigation methods: Bed-furrow irrigation system specially for row crops holds good promise for water saving than traditional basin irrigation method. Experiments conducted by Pakistan Agricultural Research Council (PARC) have shown that in bed-furrow irrigation system there is about 30 per cent water saving with 34 per cent increase in yield of maize, compared to basin.

Improved water management: Through improved water management, available water can be supplied at critical crop growth stages. This can reduce the stress leading to increased yields. By increasing water supply reliability farmers will invest more in other agricultural inputs, such as improved seed, fertilizers, etc. As a result, higher yields per unit of water can be achieved.

Optimizing agricultural inputs: In association with irrigation strategies that increase the yield per unit of water consumed, agronomic practices, such as land preparation and balanced fertilization at appropriate time through efficient methods, can increase the returns per unit of water. These can bridge seasonal drought stress through utilizing water efficiently and exploring water from depths.

Reducing non-beneficial depletion: Water lost from soil surface through evaporation is of no use to crops. This loss can be reduced through efficient irrigation methods, mulching, changing crop geometry, etc., decreasing the area of free water surfaces and decreasing non or less beneficial vegetation. The saved water will be utilized by the plants.

Exploiting shallow water: In certain areas there are shallow watertables and temporary waterlogging due to rainfalls or heavy irrigations. These areas can be cropped using bed-furrow irrigation methods. With this technology these areas can be utilized efficiently and shallow watertables can be exploited for beneficial uses. Furthermore, waterlogging problems can also be arrested.

Brackish and waste water: Through improved management strategies the brackish water and domestic waste water can be used and brought into the production system. Conjunctive use and joint management of surface and groundwater or waste water is essential to increase overall gains from crop production.

Better use of excess water: In certain parts of the year (monsoon/winter season) and certain areas, freshwater is excess compared to optimum water demands. PARC has developed technologies that this excess water is stored at farms for its utilization to irrigate crops at critical crop growth stages and bring more areas under crops. Efficient irrigation methods (sprinkler, etc.) should be preferred to make use of this stored water.

Re-allocating water among uses: The allocation of water should be made considering its economic profitability/productivity. Reallocating water from lower to high-value uses will not result in any direct water saving but it can dramatically increase the water productivity in economic terms.

Farm management: There are considerable yield differences across the farms and water courses/systems. The lower yield can be raised through proper management of resources (land, water, inputs, etc.) consequently this will improve water productivity. Existing yield gaps can be abridged by promoting improved farm management practices such as replacing old varieties with new ones, sowing of crops at optimum time, applying balanced fertilizer at optimum times and methods, and weed control.

For non irrigated conditions, water availability dictates crop production more than any other factor. Crop management practices such as rotation, planting geometries, multiple cropping, crop residue management affect water productivity directly and indirectly. In many rainfed areas there is sufficient average rainfall during the crop season to obtain good yields.

But yields are generally reduced by short term (15-30 days) droughts at critical crop growth stages. If there is a technology to store surplus rain water before these critical stages and apply it at these stages when rain fails, crop production would increase dramatically. PARC has developed technologies which can help store these excess waters at convenient places at the farms in the form of water ponds/reservoirs. To some extent this water can be stored in the fields within the soil profile by improving field bunds and water storage capacities. The groundwater can be developed in the form of dugwells and utilized for supplemental irrigation in dominantly rainfed areas with great potential for increasing water productivity and addressing poverty and local food security issues.

There is a popular idea to convert food production in rainfed rather than irrigated areas. The irrigated areas should be utilized for production of high value cash crops for export and domestic use.

Integrated land and water use: PARC has developed an integrated land and water use model which has made it possible to increase land and water productivity. By adopting water harvesting techniques with little supplemental irrigation it is possible to grow fruit plants. The crop yields have increased 2-3 times with an increase in cropping intensity.

Crop selection: In rainfed areas emphasis should be given to summer crops which make use of rainfall and provide cover to soil and protect it from erosion. By increasing the use of this rainfall, both capture efficiency and conservation efficiency of water can be improved over the year. Crops planted during this season will directly use some of the water that otherwise may leave the soil before a crop is planted in the next season. Furthermore, crops are not equal in their conversion efficiencies, defined as production of biomass per unit of water captured. Inclusion of more efficient crops by using species that are best adopted to each growing season can increase overall water use efficiencies.

Water conservation: Crops grown in rainfed production system are usually subjected to periods of drought stress of varying length and frequencies during the growing season. The mulch formed by a cover crop with conservation tillage can eliminate some of these short period drought stresses and lessen but not eliminate the effects of longer periods.

Soil organic matter: The role of soil organic matter in rainfed agriculture cannot be ignored/over-emphasized. Soil organic matter increases infiltration capacities and water storage and reduces runoff from each rainfall event so the amount of plant available water is increased.

Dr Muhammad Shafiq is Principal Scientific Officer and Dr Zahid Hussain is CSO/ Director Water Resource Research Institute NARC, Islamabad

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