Explain the concept of water use efficiency and discuss the factors that increase it with the particular reference to the situation in Pakistan. Also some of the special problems of irrigation methodology

Explain the concept of water use efficiency and discuss the factors that increase it with the particular reference to the situation in Pakistan. Also some of the special problems of irrigation methodology

Water Use Efficiency
Today agriculture uses about 70% of the global freshwater withdrawal, despite the fact that only about 20% of the agricultural land is irrigated. Agriculture is progressively more competing with industrial and private water appropriation, but the water resources are limited and scientists warn that even the current withdrawal is not sustainable anymore. Improvement in efficiency of fresh water use is, therefore, a key component of global food security. This requires considerable investments, innovative technology and know-how in the agricultural sector over the coming decades, which is rightly embraced in the so-called “blue revolution”.

Irrigation is the artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall. Additionally, irrigation also has a few other uses in crop production, which include protecting plants against frost, suppressing weed growing in grain fields and helping in preventing soil consolidation. In contrast, agriculture that relies only on direct rainfall is referred to as rain-fed or dry land farming. Irrigation systems are also used for dust suppression, disposal of sewage, and in mining. Irrigation is often studied together with drainage, which is the natural or artificial removal of surface and sub-surface water from a given area.

With agriculture responsible for the largest water usage in the United States and with irrigation dams being the most common type of water supply dam, it is important to examine the way this industry uses water and how conservation methods can be used to increase efficiencies and thus possibly decrease the need for dams. In addition to some of the alternative diversion techniques (described above) to supply water for irrigation, the U.S. EPA has compiled water-saving irrigation practices into three categories

• Field Practices
• Management Strategies
• System Modifications

When these practices are combined with the alternative diversion strategies above, the need for a diversion dam for irrigation could be eliminated in some circumstances.

Land has been tilled and terraced to better capture water (Lynn Betts, USDA Natural Resource Conservation Service)

Field practices
Field practices are techniques focused on keeping water in the field, distributing it more efficiently, or achieving better soil moisture retention. These techniques are typically less expensive than management strategies or system modifications. When traditional field practices fall short of expectations and the management strategies and systems modifications discussed below are out of reach, the field practices of dry-land farming and land retirement are another avenue to explore. Examples of field practices include:

• The chiseling of extremely compacted soils;
• Furrow diking to prevent runoff;
• Land leveling for a more even water distribution
• Dry-land farming; and
• Land retirement.

Land that has been leveled and furrow irrigated (Jeff Vanuga, USDA Natural Resource Conservation Service)

Farmers can develop land management practices that will decrease the demand on water supplies. More than half of land used for agriculture is still irrigated via a gravity flow system. This system uses soil borders, furrows, or ditches in order to allow gravity to distribute water across fields. Gravity flow irrigation methods can result in up to 50 percent water loss due to evaporation, inefficiencies in water delivery to the crop-root zone and runoff at the end of the field. The traditional gravity-fed system can be improved upon with the use of laser leveling or micro irrigation, though evaporation still leads to water loss. Laser leveling involves grading and precisely leveling the soil to eliminate any variation in the gradient and reduce slope of the field. This helps control the flow of the water and allows for more uniform soil saturation. Another method of preventing runoff is furrow diking. 

Furrow diking is the practice of building small temporary dikes across furrows to conserve water for crop production, which may also aid in preventing erosion.

If the above land management practices are not decreasing water use enough and the system modifications described below are too cost prohibitive or not an appropriate technique for a particular crop, farmers can also consider converting to dry-land farming, switching to less water intensive crops, or land retirement. Farmers practicing dry-land farming in arid regions use a variety of techniques and land management practices to minimize water loss and erosion. These techniques include coordinating seeding to the ideal soil moisture content, choosing crops more suited for arid conditions, and fallowing. Fallowing refers to a number of practices used for well over a century, such as plowing a field in late falls or early spring to clear weeds and increase soil moisture. Initial plowing breaks up the land and allows the soil to absorb more water. It also eliminates moisture-sucking weeds and creates ridges in the land that limit runoff and better capture moisture from snow. Fallowing can also involve choosing not to plant a certain field for one or more growing seasons.

Land retirement refers to a common policy of permanently or temporarily suspending farming on a particular acreage of land in exchange for financial incentives. One of the best-known land retirement programs is the U.S. Department of Agriculture’s 

Conservation Reserve Program (CRP). Through CRP, farmers are paid annual rent per acre and an additional sum for providing land cover. While CRP has typically been utilized to control the agricultural market and keep prices and quantities stable, the added value of conserving land and water resources has been given more consideration in determining compensation for land retirement since the late 1990s. This type of financial incentive is common among land retirement programs.

Advantages

Practices such as chiseling, furrow diking, and land leveling allow the land to absorb water more efficiently and results in less waste. It is also one of the most inexpensive methods of agricultural water conservation discussed in this report. Depending on the amount of land in need of irrigating and the alternative chosen, it might be possible to remove an irrigation diversion dam, particularly if used in combination with one of the alternative diversion methods described above. Dryland farming and land retirement, also discussed above, have the most to offer in terms of water savings, simply because they call for the use of little to no water, and the potential for dam removal.

Disadvantages

While chiseling, furrow diking, and land leveling help prevent runoff and allow the land to retain more water, they still do not address the overwatering that results from gravity-fed irrigation. Also, dry-land farming and land retirement practices can seem akin to suggesting that farmers go out of business. Discussions centering on these alternatives should take current use and compensation into consideration. Also, dry-land farming and land retirement practices are rarely, if ever, applied to the large agribusinesses that now dominate the industry.

Costs

As discussed above, furrowing and other land leveling practices are the least expensive irrigation alternatives discussed in this report. Actual project costs will vary depending on amount of acreage, topography of the land, and the region or country in which the farm is located. According to the 1998 Farm and Ranch Irrigation Survey, capital expenditures in the United States for farm improvements were $643 million for irrigation equipment and machinery, $138 million for construction and deepening of wells, $190 million for permanent storage and distribution systems, and $83 million for land clearing and leveling. In order for dry-land farming and land retirement to be feasible for farmers, it often must be accompanied by financial incentives like conservation easements, which involves the transfer of development and/or land use rights to a government agency or non-profit providing tax benefits or direct payment for retirement of the land.

Management strategies

Management strategies allow the irrigator to monitor soil and water conditions to ensure water is delivered in the most efficient manner possible. By collecting this information, farmers can make informed decisions about scheduling, the appropriate amount of water for a particular crop, and any system upgrades that may be needed. The methods include:

• Measuring rainfall;
• Determining soil moisture;
• Checking pumping plant efficiency; and
• Scheduling irrigation.

Farmers have to rely on a number of factors to monitor soil moisture, including temperature and humidity, solar radiation, crop growth stage, mulch, soil texture, percentage of organic matter, and rooting depth. A variety of tools for monitoring soil moisture, such as Time Domain Reflectometry (TDR) probes or tensiometers, are also available to farmers. The government of Queensland in Australia has done an effective job of compiling a fact sheet on a variety of irrigation scheduling tools, including the associated pros, cons, and costs of each. Ensuring that pumping plants are running at their most efficient also guarantees that water is being delivered to the plant and not wasted. Efficiency can be checked by examining the volume of water pumped, the lift, and the amount of energy used. A pump in need of repair or adjustment can not only waste water but also cost money.

Advantages

The management strategies described above allow for the correct amount of moisture to be delivered to the plant. When combined with system upgrades like the ones discussed below, farmers can maximize the amount of water savings and the efficiency of their land. While this is not an automatic replacement for a dam, there could be an opportunity for removal or the ability to delay construction a new barrier, depending on the size of the diversion.

Disadvantages

Monitoring the water needs of crops in the most efficient manner possible requires technological upgrades that require an initial outlay of capital. In addition to the cost of implementing these system upgrades, there may be training required to integrate new computer systems and other technologies.

Costs

Depending on extensiveness of the system, costs can vary significantly for the management strategies discussed above. For example, the average price of a tensiometer ranges from $120 to $200, with the average field requiring a minimum of four stations containing two tensiometers each, while a cprobe system containing probes, training, and software can run as much as $9,120.

The Department of Natural Resources, Energy and Mines in Queensland (DNREM), Australia has put together a comprehensive fact sheet that provides cost estimates (in Australian dollars) for a wide range of irrigation scheduling tools.

A center pivot irrigation system with drop tubes (Tim McCabe, USDA Natural Resource Conservation Service)

System modifications

System modifications, often the most expensive of the three categories, require making changes to an existing irrigation system or replacing an existing system with a new one. Typical system modifications that allow for the most efficient delivery of water are:

• Add drop tubes to a center pivot system
• Retrofitting a well with a smaller pump.

Drip Irrigation System (Jeff Vanuga, USDA Natural Resource Conservation Service)

Replacement irrigation systems include:

• Installing drip irrigation, microsprinklers, or solid set systems; or
• Constructing a tailwater recovery system.

Many farms still use inefficient irrigation techniques (e.g., traveling gun, center pivot) that apply more water than crops require. Modern irrigation technology, such as drip irrigation, micro sprinklers and solid set systems can deliver water much closer to the actual plant and achieve much greater water efficiency. ^[15] These irrigation tools are the most efficient in terms of delivering water to crops. They use the latest technologies to determine the exact amount of water a crop needs in order to grow and delivers the water directly to the plant. However, they often prove most efficient when used with vegetable and fruit tree crops and less so with dense grain crops.

Advantages

Because of the considerable amount of water used in agriculture, improving efficiency in this sector offers an opportunity to achieve significant reductions in water use. By using the latest technology available to maximize the efficient use of water, the need for some water diversions and dams can be eliminated.

Disadvantages

Switching to more efficient irrigation technologies is cost prohibitive for many farmers. Even though federal and state incentives exist, they are often inadequate to address the scope of the problem.

Costs

As mentioned above, initial costs of the latest irrigation technology can be quite high. For example, drip irrigation systems can cost on average $1,000 per acre to install necessary pumps and filters and $150 per acre per year for drip tubing. A study done by Kansas State University Agricultural Experiment Station in October 2001 compared the costs of center pivot, flood and drip irrigation systems. While the drip irrigation systems are typically more expensive to install, farmers are able to recoup some costs with savings from reduced water use.

Case Study, Irrigation Methods Israel, a country with a semi-arid, Mediterranean climate, has developed a sustainable agriculture practice that allows them to stretch their limited water resources and meet both the growing demand for human consumption and increased crop production. Since the 1980s, Israel has been using drip irrigation and micro-sprinkler techniques to expand crop output (vegetables and fruit trees). Many of these irrigation systems are computerized and depend on plant moisture sensors to operate the system automatically. This technology, combined with the use of water-efficient crops and other dry farming techniques, has resulted in an irrigation efficiency of 90 percent, compared to the 64 percent efficiency of a furrow irrigation system. Between 1975 and 1998, water requirements fell from 2.85 acre-feet/acre to 1.78 acre-feet/acre. While water efficiency increased and water use continued to decrease, agricultural output increased twelve fold. While these practices have not been used in Israel to replace water supply reservoirs, their implementation on a smaller scale in the United States could increase water efficiency to the level that the need for some dams could be eliminated.