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As cotton bolls begin to grow, fiber cells on the seed coat begin to elongate. These cells continue elongation for 3 weeks, starting with the day of flowering. Stress during this time will reduce fiber length. The following 3 weeks, a layer of cellulose is deposited daily on the inside of the cotton fiber. This is called secondary wall thickening and directly corresponds to fiber strength and micronaire. Stress during this second phase of fiber development can have detrimental effects on fiber quality.
Micronaire management requires thorough understanding of the causes of high and low micronaire. High micronaire is a common problem in many parts of the U.S. that is highly related to year and environment and the maturity of the fiber; and related to variety to a lesser degree. Low micronaire, though not as common a problem as high micronaire, still affects many growers each year. Low micronaire levels are related primarily to insufficient carbohydrate levels to adequately mature the cotton fibers. Mature fiber has relatively higher micronaire while immature fiber has low micronaire.
Micronaire can vary due to boll maturity by field, but also by the location of the boll on the plant. Bottom bolls have relatively higher micronaire and upper less mature bolls have lower micronaire. Fiber from the bolls is blended at harvest to establish micronaire for the field/variety. For this reason, harvest termination and in-season crop management along with localized weather conditions can influence crop micronaire measurements.
Remember, higher yielding crops are generally higher micronaire crops while crops terminated prematurely either by weather or harvest aids tend to have lower micronaire.
Micronaire is a measure of fiber weight per unit length and the reading is used as an indicator of fiber fineness which also relates to the maturity of the fiber. Fiber fineness and diameter is greatly impacted by environmental conditions, but is also highly genetic. If fiber development is terminated prematurely, finer fibers will result in low micronaire. Conversely if environmental conditions are good, fibers will continue to mature, resulting in coarse fibers with high micronaire.
This article is from the Cotton Management Guide, a publication with year-round advice on managing high-yielding cotton. Download the Deltapine Cotton Management Guide now or