Water Resources

Cotton Production 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 ¹, while the humid Southeast can go as low as about 18 inches.² 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 breed 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, with the reason becoming clear when the water needs of cotton are compared to the average annual rainfall levels in the U.S., shown in Figure 1. A cotton plant's water requirements are less than annual rainfall from central Texas to the East.

Figure 1 – Average annual precipitation in the United States.

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 (Figure 2), as higher value crops and land uses have displaced cotton west of Texas.

Figure 2. Harvested cotton acres in the arid west (California, Arizona, New Mexico) from 1990 to 2006.³

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 an efficiency in land use.

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References:

• ¹Hunsaker, D. 1999. Basal crop coefficients and water use for early maturity cotton. Transactions of the ASAE 42(4):927-936.
• ² Bednarz, C., J. Hook, R. Yager, S. Cromer, D. Cook, and I. Griner. 2002. Cotton crop water use and irrigation scheduling p. 61-64, In A. S. Culpepper, et al., eds. Cotton Research-Extension Report
• ³ Data from Table 5 of the 2006 Cotton and Wool Year book. Cotton and Wool Yearbook (Updated 11/2006) Stock # 89004, Economic Research Service, United States Department of Agriculture.