Water Resources

Cotton Irrigation Systems

Figure 1. Siphon tubes used to deliver water between the rows of a cotton crop

For the 35% of cotton acres receiving supplemental irrigation, there are several methods of applying the water. Some of the first irrigation systems were simply siphon tubes that were placed in a ditch and use to run water between the rows of the crop (See Figure 1), or diverting water to "flood" a basin all at one time. These approaches are referred to as "surface" irrigation systems because the water travels along the surface of the field. If the field is well-designed with the right slope, and the system is 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.

Figure 2. "Standard" center pivot system still used in humid areas to irrigated cotton where evaporation loss is not a significant concern

Figure 3. Drop lines of a LEPA irrigation system in cotton.

Another method used to irrigate crops is with sprinklers, 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" (Figure 2). The earliest versions of the center pivot had sprinklers mounted on top of the pipe carrying the water as shown in Figure 2; but in arid areas, this could 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 are replaced with drop lines that "lay" the water down between crop rows as illustrated in Figure 3.

The transition from surface to sprinkler systems is evidenced by information in Figure 4, which illustrates the percentages of irrigated cotton acres by surface and sprinkler systems.

Figure 4. Percent of irrigated cotton acres receiving water from surface and sprinkler irrigation from 1998 to 2003. ¹

Irrigation delivery methods continue to be refined to make sure producers get the "most crop per drop". Within the last two years, center pivots have been modified with on/off options, so that only those sections that require irrigation receive supplemental water. These sections include areas with better soil types, or that are located at a lower part of the field where it receives water runoff from higher areas.

Figure 5. 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.

Another 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 14 inches below the surface of the entire field (See Figure 5). However, they are 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.

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References:

• ¹Data from USDA "Farm and Ranch Irrigation Surveys".