Monday, July 22, 2024

Irrigation Tips

Cotton Watering Decisions Vary Across The Belt

Although cotton is an arid crop, farmers often turn to irrigation to provide adequate water, especially during the critical growth stages. However, across the Cotton Belt, irrigation is not a one-size-fits-all practice.


For example, all the cotton acres in Arizona are irrigated because of the arid climate and the low annual precipitation.

Crop evapotranspiration represents the amount of water lost through the process of evaporation (from soil surface) and transpiration (from plant tissues) from a crop, grown in a large field, under a given climatic condition. Photo courtesy Jacqueline Nix/Dreamstime.

In describing the water availability for cotton in Arizona, Diaa Elshikha, Ph.D., assistant professor and irrigation specialist at the University of Arizona Maricopa Agriculture Center, said, “Water availability for cotton in Arizona varies by county due to differences in water allocations. Some counties may have sufficient water for irrigation, ensuring good cotton growth, while others might face restrictions, leading to challenges for cotton farmers. However, farmers can optimize water usage by fully irrigating their cotton crops if not all their land is planted.

“Arizona cotton growers must take a proactive approach to water management for their Upland and Pima cotton crops during the critical period of July to August. Monitoring soil moisture levels is essential to ensure optimal plant growth and prevent water stress.”

Lobo Farms is flood irrigated through a series of ditches and canals like this one in Yuba County, Arizona, that are fed by the Colorado River. Photo courtesy Bailee Ott Snyder.

The UA specialist adds that employing advanced tools like soil sensors enables real-time monitoring, facilitating informed decision-making regarding irrigation timing and amount. The implementation of drip irrigation systems enhances water efficiency by delivering precise amounts directly to the plants, minimizing waste. For those utilizing flood irrigation, automatic gated systems offer improved efficiency.

“Additionally, utilizing irrigation scheduling software provides valuable insights into optimal watering schedules based on weather forecasts and crop requirements,” Elshikha said. “While deficit irrigation may be necessary, caution must be taken to avoid compromising crop growth and yield. Drip irrigation, with its uniform water distribution, simplifies this process, ensuring consistent growth across the entire field.”


In the Southwest, based on long-term Mesonet data from Altus, Oklahoma, seasonal water use for adequately watered and otherwise healthy cotton is about 30 inches in southwestern Oklahoma.

When addressing stress-sensitive periods for cotton, irrigation system type and water quality, Oklahoma State University Extension personnel noted the following:

Stress-Sensitive Periods

Fruit production, retention and shedding are closely related to the availability of soil moisture. Production is optimized with an available moisture status that allows uninterrupted development of fruiting positions while avoiding excessive vegetative development on the one hand or fruit shedding on the other.

Many producers believe it is appropriate to allow cotton plants to stress before applying the first irrigation to slow vegetative growth, force root system expansion and enhance early fruit development. While it is true excessive soil moisture during this time can cause excess vegetative growth and limit root expansion, it is important not to limit water to a point of excessive stress.

As the cotton moves through squaring and into bloom stage, over-irrigating can result in yield penalties and profit loss.

It is best to challenge cotton to expand its root system, while providing adequate water under drought conditions to allow for adequate rates of growth and maturity development. According to Cotton Physiology Today, research has shown that excessive stress prior to the first irrigation may reduce main-stem node development and result in fewer nodes above white flower at first bloom, which can ultimately reduce yield potential.

Severe moisture stress during the peak flowering period can have a pronounced negative effect on yield and fiber quality. However, stress either early or late in the blooming period results in significant yield reductions. Ideally, moisture stress should be avoided throughout the crop development period.

Early irrigations may be justified to maintain adequate, but not excessive, vegetative growth. Matching the lower water demand late in the season is key to achieve timely cutout and optimize fiber quality.

Irrigation System Type

Researchers make use of a moisture sensor on the Oklahoma State Support Program demonstration field while studying the velocity of water delivery. Photo courtesy of the Cotton Board.

Application efficiency for furrow irrigation typically ranges from 40% to 80%, and center pivot sprinkler/spray ranges from 65% to 90%. Center pivot low energy precision application (LEPA) ranges from 85% to 95%, and sub-surface drip ranges from 85% to 99%. The theoretical goal is to be 100% efficient.

If using a spray system, make sure to use nozzle applicators that generate large droplet sizes. This should help reduce evaporation issues during application. Apply at least 1 inch per application, if it can be done without causing runoff.

Larger applications will increase the depth water infiltrates into the soil, which will decrease evaporation from the soil surface. Be thoughtful not to over-apply and cause drainage. The likelihood of drainage can be better estimated if an irrigation planner or soil moisture probes are used to estimate soil moisture status.

Water Quality

Irrigation water quality should not be overlooked. High salinity water and/or saline soils can adversely affect crop performance. If high-salinity water is the only source of water input for the crop, there is a high risk the crop will ultimately suffer. These effects can vary with seasonal rainfall, soil type and soil salinity.

OSU Extension Fact Sheet PSS-2401 Classification of Irrigation Water Quality provides classification of irrigation water quality, describes how irrigation water quality is determined and the conditional use of low-quality water for various crops, including cotton. If water quality is a concern, contact your local county Extension office. Educators can send a water sample in for analysis at the OSU Soil, Water and Forage Analytical Laboratory.


MIST — Mississippi Irrigation Scheduling Tool

According to Mississippi State University Extension, the Mississippi Irrigation Scheduling Tool (MIST) relies on the most current scientific knowledge of crop water use to assist producers in making irrigation decisions. Here is how MSU says it works.

Rather than requiring the user to take readings in the field and input data, MIST automatically collects information from national and regional databases and continuously calculates crop water use.

Automatically downloading information from these databases allows growers to use MIST without requiring extensive data collection or input to the model. With MIST, there are no programs to install or maintain. The program is accessed through the internet and is available on several platforms, including smartphones, tablet computers, laptops and desktop computers. This allows the user to determine future crop water needs from any location and instantly tell when a crop needs water.

University Of Tennessee MOIST Program

Most water-balance, irrigation scheduling programs function in a similar manner, but the means of data input and the representation of the output can be very different, according to Brian Lieb with the University of Tennessee Extension. UT’s program called Management of Irrigation Systems in Tennessee (MOIST) requires weekly input of rainfall and irrigation instead of daily data. This is easier for producers to maintain and thus keep track of the needed rainfall and irrigation amounts.

The approach works fine for the more drought-tolerant row crops that are grown in the good water-holding soils of West Tennessee. However, weekly input may not be adequate for water-sensitive crops grown in low water-holding soils like sands.  For center-pivot irrigation in good water-holding soils, 1.5 inches of soil water depletion is a good target because center pivots are designed to keep up with crop water use and not to catch up or replenish the soil profile.

“MOIST provides a graphical output in addition to a table format,” Lieb says. “The program also provides a forecast type of output so that center-pivot irrigators can have a plan of action once they update data into the program.

The forecast type of output allows a producer to schedule irrigation without having to go back to the MOIST program every time a rainfall or irrigation event occurs.”


The University of Georgia Cooperative Extension Service has numerous experts who work in all aspects of cotton production, including irrigation. In a recent UGA Cotton Team newsletter, Extension personnel provided a June cotton irrigation update along with irrigation tips going forward:

While we do not want to keep an overabundance of moisture (keeping the moisture level at capacity or “full”), we do want to keep adequate moisture to maintain the crop. Once we fall behind on moisture, it’s hard to catch up on irrigation alone, unless an adequate amount of rainfall is received. When crops are utilizing moisture as fast as we apply it, it’s hard, if not impossible, to bring soil moisture back to an adequate level.

Young cotton plants do not require a lot of moisture for the first few weeks, but it is important not to stress the crop. Earlier planted cotton will be moving into first flower by the end of June. Thus, staying on top of water requirements will become critical throughout the month of June and into July for the entirety of the crop regardless of planting date.

Additionally, even later planted cotton may need some irrigation to ensure there is enough soil moisture available for the crop. Remember, if there is no rainfall, the water requirements need to come from somewhere — in this case irrigation.

In the Irrigation Reference Guide for Corn, Cotton, Peanuts and Soybeans, UGA Cooperative Extension shows estimated water requirements in days after planting (DAP) and estimated growth stage. Based on the physiological progression of the crop, it may be better to look at the growth stage and not the DAP. 

For more information about irrigating cotton in your area of the Cotton Belt, contact your local Extension agent.

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