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Cotton in the Southwestern United States
Both upland and pima cotton are grown in the Southwest. While cotton is grown only in 20% of Southwestern counties, it represents the second most lucrative regional field crop ($924M in 2012). In the Southwest region, cotton is grown in portions of Arizona, California and New Mexico (Figure 1).
Figure 1. Cotton acreage harvested by county.
Cotton is native to semi-arid deserts and requires warm temperatures. Commercial cotton species are of tropical and sub-tropical origin, require large numbers of heat units to mature, and have fair levels of heat tolerance. However, cotton can be vulnerable to heat stress, especially during humid periods. Since cotton response varies by developmental stage, plant organ and environment, there is no consensus on optimum cotton temperatures. However, yield and growth can be diminished at high temperatures (Oosterhuis 1999), especially during floral development (Snider et al. 2011). While cotton can be grown at temperatures higher than 40°C (104°F), reported ideal temperatures from studies in a controlled environment range from 20 to 32°C (68-90°F) (Burke et al. 1988, Reddy et al. 1991). Zeiher and Brown conducted field, growth chamber and greenhouse studies and found that fruit retention, seed number and boll size declined as mean temperatures increased above 28°C (82°F) and fruit retention declined at mean temperatures above 32°C (90°F) (Brown 2008). Floral abnormalities associated with heat stress occurred ~15 days after exposure to mean temperatures above 30°C (86°F) leading to the conclusion that severe heat stress damages young squares that are about 15 days from flowering, subsequently causing nearly all resulting bolls to abort 3-5 days after bloom (Brown 2008). One likely reason for elevated rates of heat stress induced sterility during the monsoon was due to higher relative humidity and reduced transpirational canopy cooling.
While temperatures outside optima inhibit growth and reproduction, ambient air temperature and cotton canopy temperatures are not equivalent in the western US. Cotton canopies can be much cooler than air temperature in arid and semi-arid regions. This is one reason cotton is still grown in the lower Arizona desert. While temperature contributes to cotton heat stress, humidity associated with the summer monsoon is the factor that most impacts Arizona cotton production. Climate change may alter the geographical area suited to cotton production, possibly to higher elevations, especially if warmer summer months also experience a more intense monsoonal season and higher humidity. Since cotton produces over the growing season, some of the impacts of climate change may be buffered because of this adaptive capacity (Walthall et al. 2012). If conditions warm to where cotton cannot be grown in the normal summer season, then production may shift to the transition seasons where solar radiation and therefore water use is lower.
All Southwestern cotton is irrigated. Temperature is a relatively minor factor when it comes to crop water use. The major factor driving water use is solar radiation which is already at high levels in the Southwestern US. In a warmer future environment, we may see a small increase in crop water use on a daily basis, but this may be offset by faster crop development.
Cotton breeders continue to select new varieties and yields are improving. Through largely conventional breeding it appears we are gaining heat and drought tolerance as the climate changes. If future warming accelerates, we may need to rely more on genetic engineering to accelerate variety improvement.
The University of Arizona Cooperative Extension hosts a website showing cotton advisories since 2011 (http://cals.arizona.edu/azmet/cotton.htm) and an excellent publication on cotton heat stress (http://www.ag.arizona.edu/azmet/az1448.pdf).
Cotton vulnerability can be characterized by considering exposure, sensitivity and adaptive capacity as described in Table 1 on a regional basis.
|Table 1. Vulnerability of cotton under a changing climate|
Leaf area can decline above mean temperatures of 35°C (95°F).
Shoot biomass decreases at 30°C (86°F).
Flowering is the most sensitive to high temperatures because of impacts on pollination and pollen tube growth (28°C to 32°C (82-90°F) optimum) for upland cultivars.
Elevated daytime temperatures decrease photosynthesis and carbohydrate production (Bibi et al. 2008).
Elevated night temperatures increase respiration and decrease carbohydrates. Temperatures higher than 30°C/20°C (86°F/68°F) day/night temperature regime caused lower boll retention in controlled environment studies (Reddy et al. 1991). Note: canopy temperatures can be much lower than ambient air temperature.
Elevations of 1°C (1.8°F) in daily maximum and minimum temperature caused a decline in seed number, which is an important basic component of cotton yield (Pettigrew 2008).
Heat adapted upland cotton cultivars had higher yields and heat resistance than advanced Pima cultivars (Lu et al. 1997).
Extension of growing season provides more flexibility in planting – early planting and two crops per year may be planted in more areas.
Cotton can be grown further north. A recent study reports simulated increases in cotton yield at high latitudes due to longer growing season and decreases at lower latitudes due to temperature and drought stress (Richardson et al. 2002)
Need increased thermal tolerance in commercial cultivars of cotton, likely drawing from foreign cultivars (Snider et al. 2011) or wild cotton strains (Bibi et al. 2010).
Canopy temperatures in the west provide some natural adaptive function. For example, while air temperatures routinely exceed 30°C (86°F) day/ 20°C (68°F) night in Arizona, canopy temperature afford cotton yields among the highest in the nation.
Genetic modification to increase thermal tolerance.
Drought stress can decrease leaf area, cotton yield and fiber quality (Loka et al. 2011).
Irrigation in dry areas and more efficient irrigation to use limited supplies.
Genetic modification to increase tolerance to drought.
CO2 is expected to increase photosynthesis, biomass production and water use efficiency with little change in lint quality.
A free-air CO2 enrichment (FACE) experiment on cotton in Arizona confirms that photosynthesis and water use efficiency increased under CO2 of 550 ppm (Hileman et al. 1994, Idso et al. 1994). Of note is that water use did not decline, but biomass increased.
Bibi, A.C.; D.M. Oosterhuis; Gonias, E.D.; Stewart, J.M. 2010. Comparison of a responses of a ruderal Gossypium hirsutum l. With commercial cotton genotypes under high temperature stress. Amer. J. Plant Sci. Biotechnol. 4: 87-92.
Bibi, A.C.; Oosterhuis, D.M.; Gonias, E.G. 2008. Photosynthesis, quantum yield of photosystem II, and membrane leakage as affected by high temperatures in cotton genotypes. Journal of Cotton Science. 12(2): 150-159.
Brown, P.W. 2008. Cotton Heat Stress. Tucson, AZ: The University of Arizona Cooperative Extension. 10.
Burke, J.J.; Mahan, J.R.; Hatfield, J.L. 1988. Crop-Specific Thermal Kinetic Windows in Relation to Wheat and Cotton Biomass Production. Agron. J. 80(4): 553-556.
Hileman, D.R.; Huluka, G.; Kenjige, P.K.; Sinha, N.; Bhattacharya, N.C.; Biswas, P.K.; Lewin, K.F.; Nagy, J.; Hendrey, G.R. 1994. Canopy photosynthesis and transpiration of field-grown cotton exposed to free-air CO2 enrichment (FACE) and differential irrigation. Agricultural and Forest Meteorology. 70(1–4): 189-207.
Idso, S.B.; Kimball, B.A.; Wall, G.W.; Garcia, R.L.; LaMorte, R.; Pinter Jr, P.J.; Mauney, J.R.; Hendrey, G.R.; Lewin, K.; Nagy, J. 1994. Effects of free-air CO2 enrichment on the light response curve of net photosynthesis in cotton leaves. Agricultural and Forest Meteorology. 70(1–4): 183-188.
Loka, D.A.; Oosterhuis, D.M.; Ritchie, G.L. 2011. Water-deficit stress in cotton. In: D. M. Oosterhuis, ed. Stress physiology in cotton. Cordova, TN: The Cotton Foundation.
Lu, Z.; Chen, J.; Percy, R.G.; Zeiger, E. 1997. Photosynthetic Rate, Stomatal Conductance and Leaf Area in Two Cotton Species (<i>Gossypium barbadense</i> and <i>Gossypium hirsutum</i>) and their Relation with Heat Resistance and Yield. Functional Plant Biology. 24(5): 693-700.
Oosterhuis, D.M. 1999. Yield response to environmental extremes in cotton. Cotton Research Meeting. Fayetteville, AR: Arkansas Agric. Exp. Stn.
Pettigrew, W.T. 2008. The effect of higher temperatures on cotton lint yield production and fiber quality. Crop Science. 48(1): 278-285.
Reddy, V.R.; Reddy, K.R.; Baker, D.N. 1991. Temperature effect on growth and development of cotton during the fruiting period. Agronomy Journal. 83(1): 211-217.
Richardson, A.G.; Reddy, K.R.; Boone, M.L. 2002. Sensitivity analysis of climate change impacts on cotton production using the GOSSYM crop model. International Journal of Biotronics. 31: 25-49.
Snider, J.L.; Oosterhuis, D.M.; Kawakami, E.M. 2011. Diurnal pollen tube growth rate is slowed by high temperature in field-grown Gossypium hirsutum pistils. Journal of Plant Physiology. 168(5): 441-448.
Walthall, C.L.; Hatfield, J.; Backlund, P.; Lengnick, L.; Marshall, E.; Walsh, M.; Adkins, S.; Aillery, M.; Ainsworth, E.A.; C. Ammann, C.J.A., I. Bartomeus, L.H. Baumgard, F. Booker, B. Bradley, D.M. Blumenthal, J. Bunce, K. Burkey, S.M. Dabney, J.A. Delgado, J. Dukes, A. Funk, K. Garrett, M. Glenn, D.A. Grantz, D. Goodrich, S. Hu, R.C. Izaurralde,; R.A.C. Jones, S.-H.K., A.D.B. Leaky, K. Lewers, T.L. Mader, A. McClung, J. Morgan, D.J. Muth, M. Nearing, D.M. Oosterhuis, D. Ort, C. Parmesan, W.T. Pettigrew, W. Polley, R. Rader, C. Rice, M. Rivington, E. Rosskopf, W.A. Salas,; L.E. Sollenberger, R.S., C. Stöckle, E.S. Takle, D. Timlin, J.W. White, R. Winfree, L. Wright-Morton, L.H. Ziska. 2012. Climate Change and Agriculture in the US: Effects and Adaptation. USDA Technical Bulletin #1935. Washington D.C.: USDA ARS Climate Change Program Office. 186pp. Available at http://www.usda.gov/oce/climate_change/effects_2012/effects_agriculture.htm.
Contributors and reviewers of this article include Emile Elias (USDA ARS), Paul Brown (AZ Cooperative Extension) and Richard Percy (USDA ARS)