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Did you know? Cotton is a very efficient user of water
A very extensive review of crop water use efficiency for wheat, rice, maize, and cotton was recently completed by the Water Watch Institute in The Netherlands (Zwart and Bastiaanssen, 20041 ). The review included 84 literature sources published in the last 25 years documenting water use studies. These studies were conducted in at least 8 countries, distributed across 4 continents for each crop. A summary of the average “water use efficiency” (WUE) for the four crops considered is presented in Table 1.
WUE is defined as the marketable crop yield divided by crop water use. As cotton’s marketable products are seed and lint, the two should be added together when comparing cotton to other crops. From the data in Table 1, it is obvious that cotton is not significantly different in its WUE from other crops. The information in this peer-reviewed publication is in sharp contrast to a preliminary report by Soth et al. (1999)2 on cotton water use, published by the WWF, which is widely-cited on the Internet. The water use efficiency erroneously reported for cotton in the Soth report is a range of 7,000 to 29,000 liters of water per kilogram (L/kg) of lint produced. This range is termed "erroneous" as, of the 66 WUE values for lint production in the studies reviewed by Zwart and Bastiaanssen, only three reported values exceeded 7000 L/kg, and none were higher than 10,000 L/kg.
As the WUE range is the basis for other statements about cotton water use in the Soth et al. (1999) report, many values in that report are exaggerated by a factor of at least 2 to 6 times the actual level.
Table 1. Average crop water use efficiency in pounds of economic yield per acre-inch of water used (lb/acre-in) and in liters of water per kilogram of economic yield (L/kg) from data compiled by Zwart and Bastiaanssen (2004).
| Crop |
Water Use Efficiency |
| lb/acre-in |
L/kg |
| Maize |
408 |
556 |
| Wheat |
247 |
917 |
| Rice |
247 |
917 |
| Cotton - Seed + Lint |
199 |
1136 |
| Seed |
147 |
1538 |
| Lint |
52 |
4348 |
There are historic cases where cotton is blamed for overuse of a water resource; however, in every case, it is the allocation policy in place, not cotton that is to blame.
References:
- 1Zwart, S.J. and G.M. Bastiaanssen. 2004. Review of measured crop water productivity values for irrigated wheat, rice, cotton and maize. Agricultural Water Management 69(2):115-133.
- 2Soth, J., C., C. Grasser and R. Salerno. 1999. The impact of cotton on fresh water resources and ecosystems, a preliminary synthesis. WWF Background Paper. 48 pp.
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