5 MIN READ
High Day or Night Temperatures Affect Cotton Yield
February 28, 2022
Yield Expectations During Stress
Heat stress causes a quick response in cotton. Although considered a warm season crop, temperatures greater than optimal can mean reproductive failure. Optimal cotton growth occurs when temperatures are less than 82.4°F with considerable yield losses with temperatures greater than 86°F.1 Heat stress events range in severity and length, and cotton plant response depends on growth stage.
Early Growth and Canopy Development
Temperatures of 95°F were observed to cause critical reductions in seedling germination potential, growth, and chlorophyll content.2 During leaf area and canopy development, established seedlings have stunted growth, hormonal imbalance, and put on fewer flowers. Canopy development is important for cotton fields as a well-developed canopy shades and cools soil surface temperatures. Cotton maintains canopy temperatures lower than air temperatures; although, high humidity coupled with high air temperature, could lead to canopy temperatures above the optimum.
Figure 1. Canopy development is critical for early cotton growth. Lateral root development decreases as soil temperatures increase to 93°F.3 Picture courtesy of Robert Nichols, U. S. Department of Agriculture, Bugwood.org
Pollination
Heat stress (average temperatures greater than 86°F) approximately 15 days before squares open can cause several flower abnormalities:1
Small flowers
Unopened flowers
Male and female flower parts develop out of synch
Anthers fail to release pollen
Filaments supporting anthers did not elongate
Bolls developed from heat-stressed flowers typically abort 3 to 5 days after bloom. Reproductive performance after heat stress is more greatly influenced by boll abscission after bloom than square loss before bloom.1 Pollen germination - pollen tube activation after pollen grain is received by the stigma – sharply declines with temperatures greater than 98.6°F. Pollen tube lengths are also significantly shorter with these higher temperatures. Inadequate pollen tube lengths mean pollinated flowers may have unfertilized ovules.
Boll Formation and Fiber Quality
Fruit retained during heat stress may have reduced seed number and boll size. Consequently, boll weight is reduced, and lint yield reductions of 98 lbs/acre have been reported as temperatures increase 1.8°F above optimal ambient air temperatures.2 Even in irrigated fields, cotton farmers experience yield loss related to heat stress.
Undesirable traits – high micronaire values and fiber strength – are reported with prevailing hot temperatures. Of all the fiber formation stages, initial fiber elongation is most sensitive to temperature stress. Photosynthates composing fiber cell walls are vulnerable to temperature swings, and even temperatures sustained near 70°F at the fiber elongation stage can reduce fiber quality.2
Drought Stress
Whole-plant water loss increases, and water use efficiency decreases with elevated temperatures. While moisture and heat stresses often coexist on the field level, they have been widely studied separately in cotton. Observations have shown combining moisture and heat stress has an additive effect on physiological and biochemical processes.2 Drought stressed plants have reductions in transpiration and turgor pressure due to stomatal closure to preserve moisture. Heat stress further reduces photosynthesis efficiency by affecting Photosystem II and reducing chlorophyll fluorescence.
Management and Mitigation
Cotton Product Selection and Genetics. Cotton breeding programs should focus selection efforts on cotton products with success under both moisture and heat stresses. While markers and identifiers for tolerance genes are being researched, farmers can select cotton products with a history of performing well under stress. These plants have a response system to stress working to stabilize growth and development, retain bolls, maintain excellent yield potential, and still produce excellent quality fiber.
Spray Applications. Plant growth regulators are used in cotton to control rank growth, but they can also be used to quickly enhance antioxidant defense. Ascorbic acid and salicyclic acid are used to fortify cell walls and could increase yield potential.2
Planting Date and Maturity. Early maturing cotton products seem to be more negatively affected by heat stress. Farmers of rainfed cotton fields should adjust planting time to try and align flowering and boll formation to occur during cooler average temperatures. Planting date adjustment had less effect on irrigated cotton.
Escape Heat. Cotton grown at higher altitudes can escape some heat stress even with greater than optimum temperatures. Reduced humidity and cooler nighttime temperatures at higher elevations help plants recover and carry out normal respiration cycles and carbohydrate accumulation. The indeterminate growth habit and fruiting pattern of cotton can be beneficial if heat stress is short or replaced by optimal temperatures during flowering stage. Some new growth may escape the effects of heat.
Conclusion
High heat events cause a stress response in cotton. This stress response and ability to cope with high heat depends on the cotton growth stage. Additionally, the severity and length of the heat event determines the cotton crop response. Although not in control of weather, cotton farmers can mitigate some of the effects of heat stress.
Sources
1 Brown, P. 2008. Cotton heat stress. University of Arizona Extension. AZ1448
2 Zafar, S.A., Noor, M.A., Waqas, M.A., Xiukang, W. 2018. Temperature extremes in cotton production mitigation strategies.
3 McMichael, B.L., and Burke, J.J. 1994. Metabolic activitiy of cotton roots in response to temperature. Environmental and Experimental Botany. Vol. 34, No 2, pp. 201-206.
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