Cotton & Natural Resources
Cotton and Water
Contrary to popular belief, cotton is a very drought-tolerant plant. And, in fact, the majority of U.S. cotton production is done so without irrigation - just the water of natural rainfall. When irrigation is used, it simply supplements rainfall during dry periods.
New irrigation systems and strategies used today, particularly in the U.S., are substantially more water efficient than in previous decades.
- Water and Cotton Production
- Water Management Overview
- Cotton Water Requirements
- Cotton Irrigation Systems
- Modern Water Management Practices
- Research to Continue Improve Water Management for Cotton and Further Details on Cotton Water Management
- U.S. Regulation of Agricultural Water Resources
- U.S. Agricultural Trends in Water Resources
- Other Resources on Cotton and Water
Water Management Overview
Existing natural water resources can sustain cotton production in many areas of the world with minimal environmental impact. Cotton has been wrongly cited as a water intensive crop, when in reality it is very drought tolerant. In fact, in many regions of the world, cotton gets all of its water from rainfall — water that would be used by whatever vegetation is present. For example, about 64% of the U.S. cotton crop is produced without irrigation, and irrigation is used in most of the remaining 35% of U.S. cotton crop only to supplement crop needs  . The cotton plant is drought-adapted and responds favorably to periods of water stress sufficient to slow vegetative growth  .
Water quality is also preserved in modern cotton productions systems. The increase in conservation tillage practices has resulted in a reduction of runoff from agricultural lands, decreasing non-point source pollution of fertilizer and pesticides. Intensive local monitoring of surface water and sub-soils has demonstrated the benefits of no-till cotton in protecting both ground and surface water resources  . Better nutrient management and precision technologies are insuring inputs are used by the crop and are not entering ground or surface waters.
Cotton Water Requirements
Like all crops, a cotton plant's water requirements vary by the environment it grows in. The dryer and hotter the environment is, the more water the plant requires. For the United States, this amount varies significantly. Moving from the West Coast to the East Coast, for example, the desert Southwest requires a maximum of about 40 inches of water per year  , while the humid Southeast can go as low as about 18 inches  . While water requirements are higher in the West, so are yields, and modern cotton varieties tend to provide at least 60 pounds of lint and 90 pounds of seed for every inch of water used. (An "inch" is a common way to describe crop water requirements, and is the same unit used to measure rainfall. The "inch" represents the depth of water per unit area.)
As cotton has been bred to be a drought-tolerant crop, in many parts for the world, it is grown without any supplemental irrigation and relies solely on rainfall. For example, only 35% of the US cotton crop is produced on irrigated land, which compares to the average annual rainfall levels in the U.S. A cotton plant's water requirements are less than annual rainfall from central Texas to the East.
Partially due to lack of affordable water resources, the amount of cotton produced in California, Arizona, and New Mexico has been steadily declining for the last decade, as higher value crops and land uses have displaced cotton west of Texas.
For other cotton areas that are irrigated, a small amount of irrigation at key times in the growing season can greatly improve yields. Viewed in this way, irrigated agriculture is consistent with the goals of sustainability because it maximizes efficiency in land use.
Average annual precipitation in the United States. The 30-year average from 1961 to 1990 developed by UDSA, NRCS, NOAA, and Oregon State University.
Harvested cotton acres in the arid west (California, Arizona, New Mexico) from 1990 to 2008  .
Cotton Irrigation Systems
For the 36% of U.S. cotton acres receiving supplemental irrigation, there are several methods of applying the water. Some of the first irrigation systems were siphon tubes that were placed in a ditch and ran water between the rows of the crop, or diverting water to "flood" a basin all at one time. This approach is referred to as "surface" irrigation (also known as flood or furrow irrigation) systems because the water travels along the surface of the field. If the field is well designed with the right slope, and properly operated, surface irrigation can be an efficient method of delivering water to crop. However, those conditions are not always met and surface systems are often very labor-intensive.
Sprinkler Irrigation Systems
Another method used to irrigate crops is with sprinklers that just like the ones many people use to water their lawns. In most cases the sprinkler irrigation systems used in cotton are mounted on a "center pivot." The earliest versions of the center pivot had sprinklers mounted on top of the pipe carrying the water but, in arid areas, this can lead to a great deal of water loss due to evaporation. Therefore, most cotton producers in arid areas use sprinklers placed just above the plant or are implementing "Low Energy Precision Application" (LEPA) systems on their pivots. These sprinklers on top of the center pivot are replaced with drop lines that "lay" the water down between crop rows.
The transition from surface to sprinkler systems is evidenced by data that show the percentages of irrigated cotton acres by surface and sprinkler systems equalizing over time.
Irrigation delivery methods continue to be refined to make sure producers get the "most crop per drop". Within the last few years, new technology has also become available that allows individual sections of a center pivot to be turned on or off. This leads to more water savings, as if there is a portion of the field that does not need irrigation (for example a low spot where rainfall collects) the pivot is programmed to turn off the sprinklers over that area.
The latest trend in cotton irrigation systems, particularly in West Texas where water resources are becoming limited, is a move to subsurface drip irrigation systems. This type of system is expensive to install and maintain, as it involves running a series of tubes about 6 to 18 inches below the surface of the entire field. However, it is a very efficient way to deliver water directly to the root zone of the plant. Tubes are spaced either under each row, or between every other row depending on the soil type and environment.
Siphon tubes used to deliver water between the rows of a cotton crop.
"Standard" center pivot system still used in humid areas to irrigated cotton where evaporation loss is not a significant concern.
Siphon tubes used to deliver water between the rows of a cotton crop.
Drop lines of a Low Energy Pressure Application (LEPA) irrigation system in cotton.
Percent of irrigated cotton acres receiving water from surface and sprinkler irrigation from 1998 to 2003.
A hole dug in a field to expose a drip line that has been buried in the soil to provide water directly to the plant.
Modern Water Management Practices
Since water is a limited resource, and due to economic constraints related to costs of water, pumping and labor needed to apply irrigation, producers are prudent in managing this resource. A number of approaches are used to decide when to irrigate, including:
- Computer models that predict water use based on the growth stage of the plant and weather data
- Soil moisture probes that determine if there is sufficient water present to meet crop needs
- Thermal infrared thermometers (IRTs) that measure the temperature of the cotton leaves — as the plant begins to run out of water, its leaf temperature will increase. Some companies are now offering thermal images so producers can see leaf temperatures across the entire farm.
Research to Continue Improve Water Management for Cotton and Further Details on Cotton Water Management
Research continues to develop more accurate and easier ways to determine crop water needs and, in fact, new instruments help researchers predict when cotton plants need water. The large pond of water in the picture serves as a reference point for research purposes.
Improving water use necessitates creative and innovative technology in agricultural production systems. Numerous emerging technologies and management schemes have been developed.
Research at the NESPAL Environmental Center at the University of Georgia has shown increased efficiency of precision water placement using a combination of center pivot irrigation, sensors to detect water needs, preset geographic maps and variable rate nozzles to vary water application in accordance with soil type and water holding capacity.  Adaptation was influenced by the declining ground water resources and the cost of pumping from increasingly deep wells. Additionally, in the past 25 years, low energy precision application (LEPA) using drop tubes in Texas has decreased water losses dramatically.
Installation of subsurface drip irrigation (SDI) has also increased and this is a desirable delivery method for supplemental crop irrigation because its installation below ground eliminates evaporation from the soil surface. In fact, studies have shown that cotton grown under SDI decreased daily crop evapo-transpiration by 75% and had the highest water use efficiency for lint production. 
The potential for introduction of reusable water into these new age irrigation systems can increase the sustainability of SDI systems even further. The introduction of pulsed-flow waters from aquaculture is one method of achieving this goal.  Wastewater effluent has also been utilized in SDI systems using both tapes with emitters  , and gravel trenches  . However, caution must be taken to monitor sodium and phosphorus levels, as well as salinity, sodicity, nutrients, trace elements, and microbial contamination  .
Salinization affects about 20-30 million ha of the world's current 260 million ha of irrigated land and limits world food production  . No data is available for cotton land, specifically. However, cotton may have an advantage in this arena because it is more tolerant to high salt levels than other crops. For agriculture, salinity can be managed through drainage, leaching during the cool season and changes to more salt-tolerant crops  , such as cotton. Cultural practices such as more frequent irrigation, water source blending, land grading and timing of fertilization make salinity management easier.
An example of a measurement system that can directly reduce the use of water is the Biologically Identified Optimal Temperature Interactive Console (BIOTIC) developed by the scientists at the USDA-ARS. The system provides irrigation scheduling based upon measurements of canopy temperatures and the temperature optimum of a given crop species  .
The threshold values to schedule an irrigation event are calculated from the thermal optimum for the plant and the amount of time that a given species can exceed a temperature threshold and adequately recover. In a three-year study of the BIOTIC for scheduling irrigation in cotton, it was determined that lint yields declined 343 kg/ha for each 1 hour that the temperature exceeded 28 C9. Information like this can help optimize productivity in relation to water use.
Agriculture biotech companies are currently developing drought tolerant crops that should be launched toward the end of this decade or early next decade. Crops with improved water use efficiency, whether through traditional breeding or biotechnology, will be extremely important because they will increase the stability of production in drought conditions.
Typical weather station used by producers to collect weather data for scheduling irrigation events.
Transmitter of a soil moisture sensor used to monitor soil moisture.
Field instrumented in ongoing research to find even better methods to determine when to apply water.
U.S. Regulation of Agricultural Water Resources
Water quality and water quantity are regulated to minimize risks to the environment and communities. Producers reduce these risks by continuing to adopt best practices that have been researched and developed by the cotton industry. In the United States, producers are subject to state and federal laws that regulate water use and quality. Some examples of such laws are presented below.
Clean Water Act: Regulation by the Environmental Protection Agency (EPA) through section 319 of the Clean Water Act (CWA) establishes a Non-point Source Management Program that includes oversight of agricultural operations  .
2002 Farm Bill: The current farm bill provides a special initiative for ground and surface water conservation, and provides incentives for producers to carry out water conservation activities, including irrigation improvements, conversion to less water intensive crops, and dry-land farming. Such incentives are likely to be preserved in the next Farm Bill  .
The following examples are typical of state-level regulation in Cotton Belt states.
Western states (including the cotton states of California, Arizona and New Mexico) have a long history of carefully allocating and monitoring water resources. A summary of all the laws associated with the Western states is available from the Bureau of Land Management (BLM) at: http://www.blm.gov/nstc/WaterLaws/abstract2.html.
Texas: Water withdraws must be permitted by the Texas Natural Resource Conservation Commission. 
Mississippi: Water quality and water withdraws are regulated by the Mississippi Department of Environmental Quality. 
Tennessee: Under the authority of the Water Resources Information Act of 2002, TCA, Section 69-8-103, water withdrawals of 10,000 gallons or more on any day in Tennessee must be registered. 
Georgia: The Georgia Soil and Water Conservation Commission oversee efforts to insure sustainable use of agricultural water resources in the state. Water withdraws require state permits and all agricultural withdraws are metered.
U.S. Agricultural Trends in Water Resources
Progress in protecting water resources is not a trend that is limited to cotton production; it is part of an overall improvement resulting from modern agricultural practices applied to many crops. The following facts apply to U.S. agriculture in general from 2006 data supplied by the U.S. Department of Agriculture (USDA) National Resource Conservation Service.
Recent Trends in Agricultural Water Management 
- More than 50 percent of the benefits from improved irrigation water management are off-site benefits and are accrued by the public.
- Improvements on irrigated acres between 1998 and 2003 have resulted in reduced water use on 18.5 million acres, improved crop yield on 18.7 million acres and decreased energy cost on 15.3 million acres.
- The U.S. Geological Survey reports the average irrigation application rate decreased from 42.6 acre-inches per acre in 1950 to 29.8 acre-inches in 2000.
- USDA Farm and Ranch Irrigation survey reports that $1.13 billion was invested in irrigation equipment, facilities, and improvements during 2003. This represents an average investment of $13,056 per farm with 73 percent of this total for irrigation equipment and machinery.
Recent Trends in Agricultural Water Quality 
- The quality of water reflects what occurs on the land.
- Six million acres of buffers help protect the water quality in the United States.
- ERS research reports links between improved management and observable changes in water quality may take 10 years before long-term changes are distinguishable from short-term fluctuations.
- The application of conservation practices for water quality benefits often provides a greater benefit to society than to the individual farmer.
- Erosion rates on cropland have dropped significantly in the last 20 years.
- Research indicates erosion reductions on private lands over the period 1982 to 1992 produced benefits to water-based recreation of $373 million.
Other Resources on Cotton and Water:
- NRCS Water Quality and Quantity Resource Page — This web site has information on all aspects of water related issues in agriculture.
- 2003 Farm and Ranch Irrigation Survey — A very detailed look at irrigation trends in U.S. for all crops, including cotton. The information is provided by USDA, National Agricultural Statistics Service.
- Food and Agricultural Organization of the United Nations (FAO) "AQUASTAT" — This site provides an international perspective on agricultural water use.
- Examples of current research to improve sustainable use of water resources — A PDF file provides some examples of research being funded by Cotton Incorporated to continue to improve our management of water resources.