Water Stewardship – United States
Improving quantity and quality
Cotton naturally tolerates drought and thrives in hot, dry conditions where water is scarce. For this reason, farmers around the world are able to cultivate cotton in areas where other crops would likely fail. Cotton’s ability to grow in water-stressed regions has unfortunately led to its misleading reputation as a water-intensive crop.1 But in many areas, including most of the U.S., cotton relies solely on rainfall, not on irrigation sourced from surface or ground water. And thanks to U.S. farmers’ and researchers’ willingness to explore new cotton varieties and improved irrigation and tillage practices, water stewardship in U.S. cotton fields continues to improve.
Cotton irrigation requirements
The U.S. has seen tremendous progress in cotton water usage since the early 1980s. Between 1980 and 2020, water application rates dropped 38% and irrigated water use efficiency – the amount of water required to produce 1 pound of cotton lint – improved significantly.4 In fact, by 2020, a little over 1 acre-inch of water was enough to produce 50 pounds of lint5 – enough lint to make more than 105 t-shirts.6
Source: Field to Market: The Alliance for Sustainable Agriculture7
In the past decade, the rate of improvement has slowed. The standardization of newer irrigation technologies is one reason; climate change has also played a significant role by increasing the frequency of prolonged droughts and intense rains that cannot soak into the soil.
U.S. growers, researchers and industry partners strive to increase resilience to climate change while meeting the industry-wide ten-year goal to further increase irrigation water use efficiency by 18% by 2025.
The industry will achieve this by pursuing a four-part strategy:
- Optimize irrigation water use through increasingly efficient water delivery systems
- Maximize rainfall capture through soil health practices and farm ponds
- Increase plant water productivity by breeding cultivars for increased drought tolerance
- Evaluate with credible metrics to ensure progress8
Evolving cotton irrigation systems and precision technologies
Carefully managed irrigation water can actually increase the sustainability of a cotton field: by preventing water stress, all inputs to the crop are utilized to their maximum efficiency (e.g., land, fertilizer, and labor).
Growers choose which irrigation system is best for their operation based on their location, typography, economics and other factors. The cotton industry has made huge strides in efficiently delivering water to the field.
Growers who use surface irrigation – in which water is applied between the rows of plants – have utilized widely available precision grading systems to slope their fields to control water movement.9 These growers have largely adopted computer hole selection, a computer-aided design program that selects the optimal water flow rate for each row and calculates the proper size hole in the irrigation pipe to achieve that rate. Growers can potentially reduce water usage and irrigation costs by 25% or more by using computer hole selection.10
Many U.S. growers have transitioned from surface to sprinkler irrigation systems, which are often mounted on a center pivot. Pivots have steadily improved over time, and many models now support variable rate irrigation. This means they have the ability to speed up and slow down to provide different amounts of water to different parts of the field based on the plants’ specific needs. Advanced pivots can also be programmed to turn off the sprinklers when pointed toward portions of the field that do not need to be watered.
In the arid Southwest, many cotton growers use a different type of sprinkler system: Low Energy Precision Application (LEPA) and other derivatives. These types of irrigation for cotton apply water directly to a small portion of soil at a low pressure. They reduce runoff and excessive evaporation while greatly improving irrigation productivity compared to surface and pivot methods in certain areas.11,12
Subsurface drip irrigation (SDI) has spread rapidly in water-limited areas over the past two decades; in the Texas High Plains alone, adoption increased from approximately 10,000 hectares in 2000 to over 180,000 hectares in 2019.13 This system, which is expensive to install and maintain, results in the highest water use efficiency for lint production by delivering water directly to the root zone of the plant. Barnes et al. (2020) cite multiple studies that have shown SDI can result in better yield and fiber quality as well as water use efficiency compared to sprinkler systems.14
Precision agriculture and advanced data models
Every type of irrigation system in use in the U.S. today benefits further from precision agriculture tools. These tools help growers decide when, where and how much to irrigate their crop, often with significant benefits.
Sensors placed at various depths in the soil help growers map and track where water is needed. Irrigation-scheduling technologies help growers more effectively choose when and where to irrigate. Growers can also remotely measure water evaporation and various plant characteristics that demonstrate whether they are receiving enough (or too much) water.
Advanced data models pull together available data on rainfall, temperature, soil and other factors. Through sophisticated algorithms, they predict cotton yield responses to various irrigation scenarios, enabling growers to make more informed decisions as they create their irrigation maps and schedules.
Data from Daystar et al. (2017) showed that producers using sensor-based irrigation were achieving 100 pounds higher yield without increased water use compared to those not using sensors.15
Cotton water management research
Innovative new technologies and management systems can improve the ease and accuracy with which growers determine and respond to cotton’s water needs. Researchers have risen to the challenge, and the diversity of conditions within the U.S. Cotton Belt make it ideal for water-related research. The U.S. cotton industry supports new and ongoing research each year. In 2022 alone, researchers across the U.S. worked on 20 active projects that advance easier and more accurate ways to determine and respond to cotton’s water needs.
Researchers in Arkansas wrapped up a five-year study in 2019 that compared the effects of soil health practices (specifically no-till and cover crops) vs. conventional practices on cotton water use efficiency and yield. Over the course of the study, acreage cultivated using no-till and cover crops required 22.5% less water to produce a pound of cotton, while also improving yield and significantly cutting down erosion.16
Soil type is another important factor in water management decisions – and research. One study in Tennessee has shown that while silt loam soils did not require irrigation under certain weather conditions, coarse textured soils benefitted from supplemental water under the same conditions.17 More recently, researchers at Texas Tech have been studying the effects of soil physical properties and field topography on irrigation rates.18 Both of these studies provide valuable insights for site-specific irrigation schedules.
Another collaboration between Cotton Incorporated and Texas Tech University has approached irrigation from a completely different angle – from above. This project leverages unmanned aerial vehicles to remotely monitor and identify soil moisture levels and crop stress conditions to update water status models so that water is applied only when and where it is needed.
Scheduling and sensing
The next frontier for cotton water research is how to better equip growers to determine a crop’s water needs and respond by easily, precisely scheduling irrigation. The industry must engage more growers in using irrigation scheduling technologies and continue improving sensor technologies and crop simulation models.19
For example, USDA Agricultural Research Service scientists have been studying and developing automated, real-time control systems for scheduling irrigation. Variable rate irrigation (as described above with sprinkler irrigations systems) has helped achieve water conservation, but the system is typically based on previously determined water application maps – it is not based on real-time crop data due to cost and the technological savvy that would require. ARS researchers have been working to change this by developing a decision support system for VRI based on wireless sensors that can be used much more easily by growers. They have collaborated with three irrigation pivot manufacturers to refine the solution they’ve developed and integrate it with existing variable rate irrigation systems.20
Putting water stewardship at growers’ fingertips
Field to Market: The Alliance for Sustainable Agriculture notes that research to develop new technologies is critical for sustained positive change – and so is community support.21 Across the U.S., industry and academic partners are creating more ways to give cotton growers hands-on opportunities to learn about irrigation technologies and increase their water use efficiency.
Outreach and farmer support take many forms. Smart Irrigation Apps, for example, continues to hone its existing cotton water scheduling app to make it valuable for western U.S. cotton growers. In eastern regions, the app currently allows cotton producers to simply pick their field on a map and provide minimal information (planting dates and soil types); the app uses this and up-to-date meteorological data to then generate daily estimates of crop water status.
Soil moisture sensors are an important tool for growers. The U.S. cotton industry supports outreach events across the country to demonstrate the value of these sensors on the farm. Mississippi State University has also established the ongoing Soil Moisture Monitoring Showcase, which enables farmers to see many different types of sensors in action and learn about the telemetry services that accompany each one.
Clemson University now offers growers a testing service to determine if their center pivot irrigation systems are working properly. The tests help growers identify and address pivot issues to prevent water waste and maximize crop yield.
Protecting water quality and aquifers
Not only does modern cotton production strive to conserve water – it also preserves water quality by reducing fertilizer and pesticide runoff. For example, when farmers use conservation tillage or cover crops to build soil health and prevent erosion, they simultaneously protect ground and surface water resources because they will reduce runoff. When they use precision agriculture technologies to apply inputs more efficiently, they help prevent any excess from escaping into water or air.
The U.S. cotton industry is supporting projects that research water detainment and retainment systems as a technique for protecting water supplies. In North Carolina, one project that launched in 2020 is documenting the water quantity and quality benefits of farm ponds, which not only store rainfall to use for irrigation but also catch and store irrigation runoff before it enters natural surface waterways. In Arkansas, researchers are investigating the feasibility of expanding the use of gravel-filled infiltration galleries to help replenish aquifers.22 Both infiltration galleries and farm ponds can provide growers valuable irrigation water supply that does not impact local aquifers or surface waters.
Cotton and water regulations
Agriculture water quality and quantity are regulated to minimize risk to the environment and people, and producers are subject to state and federal laws that regulate water use and quality. Examples of such laws include the following, which is by no means an exhaustive list.
- 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 (EPA, 2002).
- The Food, Conservation, and Energy Act of 2008: Operates several programs that assist farmers to continue adopting new technologies to improve water management and protect water quality. A specific example is the Agricultural Water Enhancement Program.
All states are subject to the federal regulations, and many have regulations that are even more stringent. Some examples include the following:
- Western states (including the cotton states of California, Arizona and New Mexico): There is a long history of carefully allocating and monitoring water resources in the West. A summary of the efforts to sustain the water resources in the Western United States was compiled by Bell and Taylor (2008).23
- Texas: Surface water withdrawals must be permitted by the Texas Natural Resource Conservation Commission.
- Mississippi: Water quality and water withdrawals 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 oversees efforts to ensure sustainable use of agricultural water resources in the state. Water withdrawals require state permits and all agricultural withdrawals are metered.
Water-wise legacy and leadership
Over the past 40 years, cotton yields have grown as cotton irrigation water use has declined.24 Improved irrigation systems and precision agriculture technologies have been leading reasons for the historic improvement. The U.S. cotton industry expects this trend to continue as new research, technologies and cotton varieties are shared with and adopted by growers.25
1 Learn more in the Transformers Foundation report “Cotton: a case study in misinformation.” 2 United States Department of Agriculture National Agricultural Statistics Service. (2019). 2019 Agricultural Statistics. 3 United States Department of Agriculture National Agricultural Statistics Service (2018). 2018 Irrigation and Water Management Survey. 4 Field to Market: The Alliance for Sustainable Agriculture. (2021.) Environmental Outcomes from On-Farm Agricultural Production in the United States. National Indicators Report, fourth edition. 5 Field to Market: The Alliance for Sustainable Agriculture. (2021.) Environmental Outcomes from On-Farm Agricultural Production in the United States. National Indicators Report, fourth edition. 6 Cotton Incorporated (2017). LCA update of cotton fiber and fabric life cycle inventory. Retrieved July 21, 2022 7 Field to Market: The Alliance for Sustainable Agriculture. (2021.) Environmental Outcomes from On-Farm Agricultural Production in the United States. National Indicators Report, fourth edition. 8 Learn more in the CottonWorks™ webinar “Pathways to Progress: Increasing Cotton’s Water Productivity” 9 Frisvold, G., Sanchez, C., Gollehon, N., Megdal, S. B., & Brown, P. (2018). Evaluating gravity-flow irrigation with lessons from Yuma, Arizona, USA. Sustainability, 10(5), 1548. Accessed July 11, 2022 10 University of Arkansas System Division of Agriculture Research & Extension. (2022). “Computerized hole selection.” Accessed July 11, 2022 11 Lyle, W. M., & Bordovsky, J. P. (1983). LEPA irrigation system evaluation. Transactions of the ASAE, 26(3), 776-781. Accessed July 11, 2022 12 Bordovsky, J. P. (2019). Low-energy precision application (LEPA) irrigation: A forty-year review. Transactions of the ASABE, 62(5), 1343-1353. Accessed July 11, 2022 13 HPWD. (2019). Annual report, High Plains Underground Water Conservation District No. 1. HPWD. Accessed July 11, 2022 14 Barnes, E. M., et al. (2020). Forty years of increasing cotton’s water use productivity and why the trend will continue. Applied Engineering in Agriculture 36(4): 457-478 15 Daystar, J. S., Barnes, E., Hake, K., & Kurtz, R. (2017). Sustainability trends and natural resource use in US cotton production. BioResources 12(1), 362-392 16 Free, A., Robertson, B., Daniels, M., and Watkins, B. (2021). “Cotton Research Verification Sustainability Program: Five Year Review. Summaries of Arkansas Cotton Research 2020. Ed. by Fred Bourland. Accessed July 11, 2022 17 Grant, T., Leib, B., Savory, H., Verbree, D., Haghverdi, A. (2017). Cotton response to irrigation and nitrogen source in differencing mid-south soils. Agronomy Journal 109(6): 2537-2544 18 Neupane, J., Guo, W., West, C., Zhang, F., Lin, Z. (2021). Effects of irrigation rates on cotton yield as affected by soil physical properties and topography in the southern high plains. PLoS ONE 16(10): 19 Barnes, E. M., et al. (2020.) Forty years of increasing cotton’s water use productivity and why the trend will continue. Applied Engineering in Agriculture 36(4): 457-478 20 Andrade, M., O’Shaughnessy, S., Evett, S. (2020.) ARSPivot, a sensor-based decision support software for variable-rate irrigation center pivot systems: Part A. Development. Transactions of the ASBE. 63(5): 1521-1533. Accessed July 11, 2022 21 Field to Market: The Alliance for Sustainable Agriculture. (2021.) Environmental Outcomes from On-Farm Agricultural Production in the United States. National Indicators Report, fourth edition. 22 Godwin, I., Reba, M., Leslie, D., Adams, R., Rigby, J. (2022). Feasibility of farm-scale infiltration galleries for managed aquifer recharge in an agricultural alluvial aquifer of Northeast Arkansas. Agricultural Water Management 264 (30) 23 Bell, C., and J. Taylor. (2008). Water laws and policies for a sustainable future: a western states’ perspective. A report prepared by the staff of the Western States Water Council. Retrieved July 21, 2022 24 Field to Market: The Alliance for Sustainable Agriculture. (2021.) Environmental Outcomes from On-Farm Agricultural Production in the United States. National Indicators Report, fourth edition. 25 Barnes, E. M., et al. (2020.) Forty years of increasing cotton’s water use productivity and why the trend will continue. Applied Engineering in Agriculture 36(4): 457-478