How Water Stress Affects Cotton Crops

Even as U.S. cotton production soars to record highs, water stress looms large at the back of most American cotton farmers’ minds. While water shortages will adversely affect any crop, a cotton field’s water inputs have to be monitored very closely, as the water requirements must vary throughout a cotton plant’s life cycle for an optimum boll yield.  In tropical and subtropical zones with both wet and dry seasons where cotton is cultivated, this does not present much of an issue. In the United States, however, the vast majority of cotton fields require irrigation to ensure optimum yields.

This is not necessarily a huge problem. The United States has most of its cotton crop in arid and semi-arid areas and relies on irrigation for the vast majority of its cotton fields. Yet it is the world’s largest exporter of cotton, and third overall in production volume, after China and India.

How Water Stress Affects Cotton Crops

Irrigation of cotton creates many advantages for cotton growers, allowing them to better manage yields, keep away pests, and prevent disease. Growing cotton in an arid area and irrigating as needed also presents advantages as well, as cotton is salt-tolerant and can withstand extended dry spells. However, the amount of water and the timing of irrigations is crucial, as waterlogged cotton fields will not produce optimum yields either.

Threats to Water Security

Without enough water to irrigate fields, concerns over waterlogged cotton may become moot. In recent years, however, the overexploitation of water resources worldwide has put undue stress on existing supplies. The world’s largest cotton-producing region in the South Plains region of northwest Texas, for instance, has seen many wells and aquifers exploited for cotton run dry, causing many farmers to switch to crops less sensitive to water shortages. This is one of the better outcomes for water stress. Improper cotton irrigation practices have led to massive ecological disasters in Uzbekistan, where water supplies were overtapped, leading to desertification, and the draining of the once-massive Aral Sea.

Another cause of water stress on cotton production is climate change. A pattern of increasing temperatures and less predictable rain patterns has made it increasingly difficult for American cotton growers to rely on rains to supplement irrigation. This unpredictability also makes it difficult for growers to correctly time irrigation and other inputs in the critical early stages of a crop’s cycle.  Water tables have also decreased, thanks to the lack of regular rainfall to top off losses from human consumption. The 2011 drought saw 55 percent of cotton fields abandoned, and a financial loss of $2.2 billion. Increasing temperatures have also created conditions suited for weeds, which consume even more water and further reduces cotton yields.

Mitigating Water Stress through better Monitoring

Given all these threats to water security, the need for more accurate water monitoring is more crucial than ever. Traditionally, this is a slow process, with growers needing to take readings from only a few plants in each crop block since it would be impractical to take readings of every plant in a field. This makes it all too easy to miss potentially important irrigation issues.

Water stress monitoring through aerial spectral imagery, on the other hand, provides a much more thorough and detailed picture of water stress levels present on any farm. As cotton plants run out of water, their leaf temperatures increase. This reading is compared with ambient heat to give cotton growers an idea of current water stress levels. While satellite imagery may capture the water stress levels in an area as large as a city block, aerial spectral imagery can capture water stress levels at every cotton plant in a field, saving time and allowing growers to make decisions on water usage at a precise level.

Aerial spectral imagery provides other benefits as well. It can be used to identify priority areas for farm workers to assess in person. This saves time and eliminates the need for a “shotgun approach” towards cotton cultivation. This allows growers to use less labor for a larger area in the critical early stages of the cotton crop.

Conclusion

With the world consumption of cotton set to exceed production for the third consecutive season this year, the pressure is on to ensure that planters are up to the challenges presented by the current and future water shortages. Better water monitoring can provide a way to both mitigate risks and optimize currently available water inputs, without the grower having to switch strains or crops.