Irrigating Wisely to Conserve Water Resources

Water is a precious resource, and conserving it is crucial for our planet's future. In fact, a staggering 70% of global freshwater is used for irrigation, which is a significant portion of the world's water supply.

To irrigate wisely, it's essential to understand the concept of "crop coefficient", which helps determine the amount of water a crop needs to grow. This coefficient varies depending on factors like crop type, climate, and soil type, as seen in the example of corn, which has a relatively high crop coefficient of 1.2.

By applying this knowledge, farmers can optimize their irrigation systems, reducing water waste and ensuring their crops receive the right amount of moisture. This, in turn, leads to healthier plants, increased yields, and a more sustainable agricultural practice.

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Surface irrigation is the oldest form of irrigation, used for thousands of years. It involves water moving across the surface of agricultural lands to infiltrate into the soil, following gravity or the slope of the land.

Surface irrigation can be subdivided into furrow, border strip, or basin irrigation, and is often called flood irrigation when the land is flooded or near flooded. Historically, it's the most common method used across most parts of the world.

Surface irrigation has a lower capital cost and energy requirement compared to pressurized irrigation systems, making it a popular choice for developing nations, low-value crops, and large fields.

Subirrigation is a method of artificially raising the water table to allow the soil to be moistened from below the plants' root zone. It's often used in field crops in areas with high water tables and can be combined with drainage infrastructure.

Subirrigation is also used in commercial greenhouse production, usually for potted plants, where water is delivered from below, absorbed by upwards, and the excess collected for recycling. This type of subirrigation requires fairly sophisticated, expensive equipment and management.

In subirrigation systems, water is typically delivered for a short period, 10-20 minutes, and then pumped back into a holding tank for reuse. This approach allows for water and nutrient conservation, as well as labor savings through reduced system maintenance and automation.

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Tobacco production in Georgia relies heavily on irrigation, especially during periods of rainfall deficit. Research has shown that both under-watering and overwatering can significantly reduce tobacco yield and quality.

A self-watering container, also known as a sub-irrigated planter, is a type of subirrigation that consists of a planter suspended over a reservoir with some type of wicking material, such as a polyester rope. The water is drawn up the wick through capillary action.

Soil infiltration rate is a critical factor in irrigation, and it's influenced by soil compactness, structure, organic content, and the presence of plant material on the surface.

In the southeastern United States, the infiltration rate of most soils used for tobacco production varies from 3 in. per hour for coarse textured soils to as little as 0.5 in. or less per hour for sandy clay loams.

Water applied faster than the soil can absorb runs out the end of the row, wasting water and energy, and reducing the accuracy of water intake estimates.

As tobacco plants grow, their size reduces infiltration, causing water to be shed toward the middle of the rows, increasing the danger of runoff.

The infiltration rate is significantly reduced as the tobacco plant grows, making it essential to consider soil infiltration rate when designing irrigation systems.

Surface irrigation is the oldest form of irrigation and has been in use for thousands of years.

It involves moving water across the surface of agricultural lands to wet it and infiltrate into the soil, relying on gravity or the slope of the land to guide the water flow.

Surface irrigation can be subdivided into furrow, border strip, or basin irrigation, and is often called flood irrigation when the irrigation results in flooding or near flooding of the cultivated land.

Historically, surface irrigation is the most common method of irrigating agricultural land across most parts of the world.

It has a lower water application efficiency compared to other forms of irrigation, due in part to the lack of control of applied depths.

Surface irrigation involves a significantly lower capital cost and energy requirement than pressurized irrigation systems.

This makes it an attractive option for developing nations, low-value crops, and large fields.

Surface irrigation is even used to water urban gardens in certain areas, such as in and around Phoenix, Arizona.

The irrigated area is surrounded by a berm and the water is delivered according to a schedule set by a local irrigation district.

In some cases, surface irrigation is used in conjunction with pumping or lifting water by human or animal power to the level of the land.

Spate irrigation, also called floodwater harvesting, is a special form of surface irrigation that uses water from floods to grow crops.

This method is particularly effective in semi-arid or arid, mountainous regions where water is scarce.

Efficiency is key when it comes to irrigating, and modern methods are designed to supply the right amount of water to each plant. This ensures that each plant gets the water it needs, neither too much nor too little.

Field Water Efficiency can be determined by the formula: (Water Transpired by Crop ÷ Water Applied to Field) x 100. This simple calculation helps farmers gauge how efficiently their irrigation system is working.

Increased irrigation efficiency has a number of positive outcomes for farmers, including higher yields and lower costs. By applying less water to an existing field or using water more wisely, farmers can achieve higher yields in the same area of land.

Low application efficiency means that excess water is lost through seepage or runoff, which can result in loss of crop nutrients or pesticides. This can have adverse impacts on the surrounding environment.

A reduction in water use on one field can mean that the farmer is able to irrigate a larger area of land, increasing total agricultural production. This is a win-win for farmers and the environment.

Improving the efficiency of irrigation is usually achieved in one of two ways: by improving the system design or by optimizing the irrigation management.

Irrigation can have a significant impact on the environment and society. Negative impacts frequently accompany extensive irrigation, including the drying up of water sources, leading to a more extreme regional climate.

Some irrigation projects have relied too heavily on groundwater, causing subsidence and salinization. This can damage crops and contaminate drinking water. Pests and pathogens thrive in irrigation canals and ponds, leading to regional outbreaks of diseases like malaria and schistosomiasis.

Competition for surface water rights and territory defense are social aspects of irrigation that can be contentious. Governments have used irrigation schemes to encourage migration, often favoring more desirable populations.

The environmental impact of irrigation can be severe, with effects including altered soil and water quality, and changes to natural and social conditions in river basins and downstream areas.

Irrigation can have far-reaching environmental consequences. Extensive irrigation can dry up water sources, leading to a more extreme regional climate.

Groundwater over-pumping is another significant issue. When we pump too much water from underground aquifers, it can cause subsidence and salinization, damaging crops and contaminating drinking water.

Irrigation can also create ideal breeding grounds for pests and pathogens, leading to regional outbreaks of diseases like malaria and schistosomiasis.

Some irrigation projects have even failed to deliver on their promises, leaving behind a trail of debt and environmental degradation.

Here are some examples of areas where groundwater over-pumping has had devastating effects:

These regions are now facing a future of food production threatened by the permanent loss of aquifer capacity and decreased water quality.

Social Aspects play a crucial role in the management of water resources.

Competition for surface water rights can lead to disputes and conflicts over territory defense.

Assisting smallholders in sustainably managing irrigation technology is essential for collective success.

Collectively managing irrigation technology and adapting to changes in technology can be challenging, but it's a crucial step towards sustainability.

Here are some key social aspects to consider:

Wastewater treatment is a crucial step in ensuring the safe use of wastewater in agriculture. In some cases, treated or untreated wastewater is used for irrigation, which can serve as a fertilizer if it contains nutrients like nitrogen, phosphorus, and potassium.

Using recycled municipal wastewater for irrigation can be a cost-effective and reliable option, especially in areas with water restrictions. Cities can provide lucrative markets for fresh produce, making it attractive for farmers to use wastewater for irrigation.

However, using untreated municipal wastewater in agriculture can pose significant health hazards due to the presence of chemical and biological pollutants. In low-income countries, there are often high levels of pathogens from excreta, while in emerging nations, there are increasing risks from inorganic and organic chemicals.

The World Health Organization developed guidelines for safe use of wastewater in 2006, advocating a 'multiple-barrier' approach to wastewater use. This approach encourages farmers to adopt various risk-reducing behaviors, such as ceasing irrigation a few days before harvesting to allow pathogens to die off in the sunlight.

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After transplanting, tobacco needs about 0.5 in. of water to settle the soil around the roots and stimulate fast root development.

You can determine if your tobacco crop needs irrigation by observing its appearance - if it's showing signs of wilting before 1:00 a.m., it's likely time to water.

During the rapid growth stage, from 2 ft high to early bloom, maintain moisture levels near field capacity to support leaf expansion and internode elongation.

If the soil appears ashy in color and void of all moisture, it's a good indication that irrigation is necessary.

Tobacco produced in areas that typically dry during the production season can benefit from a balance sheet approach, tracking plant water use and moisture application.

As the plant approaches maturity, it requires less water, but still needs adequate moisture for proper maturing and curability.

Lawn sprinkler systems are typically installed in residential lawns, commercial landscapes, and public parks, with most components hidden underground to maintain aesthetics. A typical system consists of one or more zones, limited by the capacity of the water source, and may include zones with drip irrigation, bubblers, or other types of equipment.

Sprinklers can be either pop-up spray heads or rotors, with spray heads used for smaller areas and rotors for larger areas. Golf course rotors can be so large that a single sprinkler is combined with a valve and called a 'valve in head'. In flower beds or shrub areas, sprinklers may be mounted on above-ground risers.

A variety of irrigation systems are available for overhead irrigation of crops, including gun sprinkler systems, center pivot systems, and self-propelled lateral move sprinkler systems.

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Drip irrigation is a highly efficient method of irrigation, with a field water efficiency of 80 to 90% when managed correctly.

This system delivers water at or near the root zone of plants, one drop at a time, minimizing evaporation and runoff.

Drip irrigation can be combined with plastic mulch to further reduce evaporation and is also used to deliver fertilizer, a process known as fertigation.

The system can range from high-tech and computerized to low-tech and labor-intensive, with lower water pressures needed than most other types of systems.

Pressure compensating emitters are available to regulate pressure on steep slopes, eliminating the need for a level field.

A drip irrigation system typically includes a water source, pump, filters, main line, water meter, check valve, low pressure drain, vacuum breaker, pressure reducer, manifold, injection pump for adding fertilizer, sub mains and drip tube with emitters.

Some of the benefits of using drip irrigation include efficient water use, the possibility of injecting fertilizer through the system, and reduced soil erosion from surface water runoff on rolling terrain.

However, drip irrigation can be expensive to install, with the cost of wells and system components ranging from $600 to $1,500 per acre in the United States.

To get the most out of drip irrigation, it's essential to schedule irrigation based on production experience, crop observation, a water balance sheet, and moisture blocks.

Here are some approximate values of seasonal crop water needs:

Lawn sprinkler systems can be installed in residential lawns, commercial landscapes, and public parks, with most components hidden underground for aesthetic purposes.

A typical lawn sprinkler system consists of one or more zones, each covering a designated portion of the landscape, and may include zones with drip irrigation, bubblers, or other types of equipment.

Spray heads have a fixed spray pattern and are used to cover smaller areas, while rotors have one or more streams that rotate and are used for larger areas.

Golf course rotors can be so large that a single sprinkler is combined with a valve and called a 'valve in head'.

Hose-end sprinklers are devices attached to the end of a garden hose, used for watering lawns, gardens, or plants, and come in various designs and styles.

Travelling sprinklers move along the hose path on their own, watering as they go, ideal for covering long, narrow spaces.

Center pivot irrigation systems use several segments of pipe joined and supported by trusses, mounted on wheeled towers with sprinklers positioned along its length.

Lateral move systems are less expensive to install than center pivots but are more labor-intensive to operate, applying water in a stationary strip that must be drained and then rolled to a new strip.

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Drip irrigation delivers water to plants under low pressure through emitters spaced uniformly along the length of plastic tubing, reducing water use by 30 to 50 percent.

A drip irrigation system includes a water source, pump, filters, main line, water meter, check valve, and other components that work together to deliver water to the plants.

The minimal pump operating pressure for a drip irrigation system is a distinct advantage, delivering water through the drip tubing at 10 to 15 psi.

A water supply that is clean of micro flora growth and chemical contaminants is required for drip irrigation, as contaminated water can clog filters and emitters.

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Irrigation schemes involve solving numerous engineering and economic problems while minimizing negative environmental consequences. Ground subsidence, like in New Orleans, Louisiana, is a major issue.

Underirrigation or irrigation giving only just enough water for the plant can lead to poor soil salinity control, causing increased soil salinity and toxic salts on the soil surface in areas with high evaporation. This requires regular leaching to remove these salts and a method of drainage to carry them away.

Overirrigation wastes water, chemicals, and may lead to water pollution due to poor distribution uniformity or management. For example, in Australia, over-abstraction of fresh water for intensive irrigation activities has caused 33% of the land area to be at risk of salination.

Drainage front instability, also known as viscous fingering, can result in an unstable drainage front with a pattern of fingers and viscous entrapped saturated zones. This can be a problem in areas with high irrigation.

Irrigation with saline or high-sodium water can damage soil structure due to the formation of alkaline soil. This can lead to reduced crop yields and other problems.

Clogging of filters, such as those caused by algae, can be a major issue in irrigation systems. Chlorination, algaecide, UV, and ultrasonic methods can be used to control algae in irrigation systems.

Accurately measuring irrigation performance can be complicated due to changes over time and space. This requires careful consideration of measures such as productivity, efficiency, equity, and adequacy.

Macro-irrigation, typical in intensive agriculture, can cause eutrophication when agrochemicals are used. This can have negative impacts on the environment and ecosystem.

Holding Capacity is crucial for determining the need for irrigation. Soil's water-holding capacity is influenced by the size of its pore spaces.

Soil with large pore spaces, like sand, drains water quickly due to gravity. This is in contrast to fine textured soils like clay or silt, which take longer to drain.

Tobacco plants can use both water that drains by gravity and that held by soil particles. However, some moisture is held too tightly and is unavailable to plants.

A majority of flue-cured tobacco is grown on loamy sand or sandy loam soils with an available water-holding capacity between 0.7 and 1.5 inches of water in the root zone.

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The earliest known irrigation systems date back to ancient Sri Lanka, where the Sinhalese built complex systems with artificial reservoirs and canals to irrigate paddy fields around 300 BCE.

The oldest known hydraulic engineers were Sunshu Ao and Ximen Bao of ancient China, who worked on large irrigation projects in the 6th and 5th centuries BCE.

In North America, the Hohokam culture built extensive irrigation networks along the lower Salt and middle Gila Rivers between the 7th and 14th centuries, rivaling the complexity of those used in the ancient Near East, Egypt, and China.

The Hohokam cultivated a variety of crops, including cotton, tobacco, maize, beans, and squash, using their irrigation systems to support a large population in the Southwest.

The Tana River Irrigation Scheme in eastern Kenya, completed between 1948 and 1963, opened up new lands for agriculture, but the water cost four to ten times more than the crops it produced were worth.

In Egypt, modern irrigation began with Muhammad Ali Pasha in the mid-1800s, who sought to achieve Egyptian independence from the Ottomans through increased trade with Europe, specifically cotton exportation.

The global scale of irrigation increased dramatically over the 20th century, with 352 million hectares equipped for irrigation by 2021, a 22% increase from 2000 and more than twice the 1960s land area equipped for irrigation.

By 1990, 30% of the global food production came from irrigated land, and irrigation techniques across the globe include canals redirecting surface water, groundwater pumping, and diverting water from dams.

The history of irrigation is a long and fascinating one, with roots dating back thousands of years. In ancient China, hydraulic engineers like Sunshu Ao and Ximen Bao worked on large irrigation projects as far back as the 6th and 5th centuries BCE.

The oldest known hydraulic engineers of China, Sunshu Ao and Ximen Bao, were instrumental in developing large-scale irrigation systems. The Dujiangyan Irrigation System, built in 256 BCE, is still supplying water today.

Irrigation systems were also developed in ancient Sri Lanka, with the earliest dating back to around 300 BCE. The Sinhalese people built artificial reservoirs and complex canal systems to irrigate paddy fields.

These ancient irrigation systems were incredibly advanced, with features like underground canals and artificial reservoirs. The system in Sri Lanka was extensively restored and extended during the reign of King Parakrama Bahu in the 12th century CE.

By the 2nd century CE, the Chinese were using chain pumps to lift water from lower to higher elevations, powered by manual foot-pedal or hydraulic waterwheels.

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The earliest agricultural irrigation canal system known in the area of the present-day United States dates to between 1200 BCE and 800 BCE and was discovered in Marana, Arizona, by Desert Archaeology, Inc. in 2009.

This ancient irrigation system predates the Hohokam culture by two thousand years and was built by an unidentified culture.

The Hohokam culture is notable for relying heavily on irrigation canals to water their crops, and their irrigation systems supported the largest population in the Southwest by CE 1300.

Between the 7th and 14th centuries, the Hohokam built and maintained extensive irrigation networks along the lower Salt and middle Gila Rivers that rivaled the complexity of those used in the ancient Near East, Egypt, and China.

The Hohokam cultivated a variety of crops, including cotton, tobacco, maize, beans, and squash varieties, and harvested wild plants for food and fiber.

Their reliance on canal irrigation allowed them to aggregate rural populations into stable urban centers in their desert environment.

The Hohokam also used extensive dry-farming systems, primarily to grow agave for food and fiber, late in their chronological sequence.

In South America, ancient civilizations harnessed the power of irrigation to support agriculture in the desert of northern Peru.

The oldest known irrigation canals in the Americas are found in the Zaña Valley near the hamlet of Nanchoc, with radiocarbon dates suggesting they're at least 3400 BCE old.

These canals once irrigated crops like peanuts, squash, and manioc, as well as chenopods, a relative of Quinoa.

Later, maize was also grown using these ancient irrigation systems.

The Soviet Central Asia region is a fascinating case study in irrigation history. The native Kazakhs, Uzbeks, and Turkmens used minimal irrigation before the Bolsheviks conquered the area in 1917.

The Slavic immigrants brought their own irrigation methods, including waterwheels and underground irrigation channels, which the Russians initially dismissed as crude and inefficient.

Tsarist officials, however, maintained these systems through the late 19th century. The Russian government even accepted a 1911 American proposal to send hydraulic experts to Central Asia to investigate large-scale irrigation potential.

A 1918 decree by Lenin encouraged irrigation development in the region, which began in the 1930s. Stalin and other Soviet leaders prioritized large-scale, ambitious hydraulic projects, especially along the Volga River.

The Soviet irrigation push was mainly driven by fears of the American cotton monopoly and a desire to achieve cotton self-sufficiency. They built dams on the Don and Kuban Rivers for irrigation, which removed freshwater flow from the Sea of Azov and made it much saltier.

Depletion and salinization scourged other areas of the Russian irrigation project. By 1975, the USSR used eight times as much water as they had in 1913, mostly for irrigation.

Here's a rough breakdown of the USSR's water usage increase:

Note: The exact units are not specified in the article, but this gives you an idea of the massive increase in water usage.

Africa has a rich history of irrigation, shaped by colonial forces and economic ambitions. The Tana River Irrigation Scheme in eastern Kenya, completed between 1948 and 1963, opened up new lands for agriculture.

The Kenyan government attempted to resettle the area with detainees from the Mau Mau uprising. This irrigation scheme was a result of colonial influence.

Italian oil drillers discovered Libya's underground water resources during the Italian colonization of Libya. This discovery laid the groundwork for future irrigation projects.

The Great Man-Made River, built in 1969, delivered Saharan water to the coast and largely contributed to irrigation. However, it cost four to ten times more than the crops it produced were worth.

In 1912, the Union of South Africa created an irrigation department and began investing in water storage infrastructure and irrigation. This marked a significant shift in the country's approach to irrigation.

The government used irrigation and dam-building to further social goals like poverty relief by creating construction jobs for poor whites and irrigation schemes to increase white farming. The Hartbeespoort Dam, begun in 1916, was one of their first significant irrigation projects.

Modern irrigation in Egypt began with Muhammad Ali Pasha in the mid-1800s, who sought to achieve Egyptian independence from the Ottomans through increased trade with Europe. He proposed replacing traditional Nile basin irrigation with irrigation barrages in the lower Nile.

Egypt devoted 105,000 ha to cotton in 1861, which increased fivefold by 1865. Cotton production became a crucial part of the Egyptian economy.

Immediately after transplanting, tobacco should be irrigated with about 0.5 in. of water to help settle the soil around the roots and stimulate fast root development.

Tobacco requires an average of 1 in. per week of water for good growth, which can vary depending on factors like soil type and climate.

Moisture levels should be maintained near field capacity during the rapid growth stage, as leaf expansion and internode elongation are often severely restricted if adequate water is not available.

The need for irrigation can often be determined by simply observing the appearance of the crop and soil, such as if tobacco shows signs of wilting before 1:00 a.m. or if the soil appears ashy in color and void of all moisture.

In areas typically dry during the production season, tobacco can be irrigated based on a balance sheet approach, which tracks plant water use and moisture application.

Water loss from the soil occurs through the process of evaporation, while water loss from the plant results from transpiration, or moisture loss as vapor through plant leaves.

After transplanting, tobacco needs about 0.5 in. of water to settle the soil around the roots and stimulate fast root development.

If you notice your tobacco plants showing signs of wilting before 1:00 a.m., it may be time to irrigate. The soil should be moist, not dry, to support healthy growth.

During the rapid growth stage (2 ft high to early bloom), maintain moisture levels near field capacity to prevent leaf expansion and internode elongation from being restricted.

Tobacco requires less water as it approaches maturity, but adequate water is still necessary for proper maturing and curability.

If the soil appears ashy in color and void of all moisture, it's likely time to irrigate your tobacco crop. This is especially true for areas that are typically dry during the production season.

For another approach, see: Best Time to Irrigate Lawn