BY SCOTT STANISLAV, Deltapine® Technical Agronomist, Southern Texas
The 2022 growing season will be remembered for being excessively dry and hot, with many growers comparing the year to the weather that was experienced during 1980 and 2011. When a season presents us with these types of conditions, it is understood that overall cotton yield can be adversely affected, but what is less understood is how cotton fiber quality is affected.
Cotton fiber quality is a complex relationship between the genetics of the cotton variety and the growing environment experienced by the variety. Some fiber quality parameters are strongly genetic, such as fiber strength, while others are highly influenced by environmental conditions during the season, such as color grade. Micronaire and fiber length are two fiber quality characteristics affected by both the genetics and the environment.
FIBER LENGTH
To understand fiber length and how it is affected by heat and drought, we first must gain a better understanding of when fiber length starts to set in the boll. The fiber elongation phase of a given boll starts when the flower is pollinated and continues to elongate for the next 16 to 22 days. Once that time is up, cotton fiber length is set. In dryland cotton production, there are a few factors that can lead to a reduced fiber length, and these include lack of water availability to the crop, higher-than-normal temperatures and low potassium availability — either because less than adequate rates were applied to the crop or drought has restricted the root’s ability to access potassium from the soil.
MICRONAIRE
Once fiber elongation (fiber length) is complete, fiber begins to mature. Micronaire is a measurement of fiber fineness and maturity, but it doesn’t separate one from the other. Across the southern part of Texas, higher micronaire values are common when compared to other parts of the state, even in normal growing conditions. In years like 2022, when excessive drought and heat come into play, some of the elevated micronaire values can be explained. As fiber length is reduced due to stress, the plant continues to allocate the same number of resources toward fiber maturation, but doing that to an overall shorter-length fiber causes potential for higher micronaire measurement.
Another reason for higher micronaire values, especially during periods of excessive heat and drought, is when plants retain mostly bottom bolls and shed a high percentage of the middle and top bolls. Cotton bolls lower on the plant typically have a higher micronaire measurement, while middle and especially top bolls have a lower micronaire value. When middle and top bolls are missing from the plant, the average micronaire will be higher since lower micronaire bolls are missing. The two scenarios mentioned typically go hand in hand during growing seasons of severe drought and above-normal temperatures.
FIBER STRENGTH
While micronaire is influenced by genetics and environment, fiber strength is a quality parameter that is highly influenced by the genetics of the variety. However, there are some relationships and effects on fiber strength driven by growing conditions.
During periods of heat and drought stress, the inability of the cotton plant to be able to access nutrients, specifically potassium, has been shown to reduce fiber strength. Potassium has long been known as a quality nutrient in cotton, and as fiber quality in cotton varieties has improved over the years, having sufficient potassium available to the plant is more critical than ever to ensure high-quality cotton is harvested. Field weathering of exposed cotton lint from sunlight, high temperatures and rainfall can also affect fiber strength. Timely harvest can help avoid as much of this as possible.
There are many factors that are out of our control, specifically what the temperatures are going to be and how often it is going to rain. I always say control what we can control growing a cotton crop. Although we can’t choose when we are going to be faced with a year of higher-than-normal temperatures and drought, we can control our inputs, including:
- Planting a high-quality variety.
- Fertilizing properly (especially potassium).
- Managing the crop properly with plant growth regulators.
- Harvesting as timely as possible.
These factors can help mitigate risk for fiber quality losses in a season of high heat and drought stress.
Sources: https://www.cotton.org/tech/physiology/cpt/fiberquality/upload/CPT-v12No1-2001-REPOP.pdf https://www.cotton.org/tech/physiology/cpt/fiberquality/upload/CPT-Sep90-REPOP.pdf https://www.cottoninc.com/quality-products/nonwovens/ cotton-fiber-tech-guide/cotton-properties/#:~:text=Fiber%20 Strength&text=Results%20are%20reported%20as%20 grams,one%20tex%20unit%20in%20size
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